Ray Tracing News

"Light Makes Right"

September 28, 1993

Volume 6, Number 3

Compiled by Eric Haines erich@acm.org . Opinions expressed are mine.

All contents are copyright (c) 1993, all rights reserved by the individual authors

Archive locations: anonymous FTP at ftp://ftp-graphics.stanford.edu/pub/Graphics/RTNews/,
wuarchive.wustl.edu:/graphics/graphics/RTNews, and many others.

You may also want to check out the Ray Tracing News issue guide and the Mother of all Ray Tracing Pages.



Another SIGGRAPH has come and gone, and it was pretty fun for me from a Ray Tracing News perspective. I got to meet some of the creators of POV, the ray tracer derived from DKB that's been taking the CompuServe (CIS for short) world by storm. The CIS world is a different kind of place than the Internet. There be demigods there that can give you various free privileges if they deign that what you are doing is entertaining to the masses (and so generates connect time revenues).

The ray tracing technology available on CIS seems a bit old-fashioned, with things like QRT and DBW still in active existence there and in the general BBS world among some users. POV 1.0 doesn't have an automatic efficiency scheme, something that dates back at least five years with MTV's introduction on the Internet. However, I suspect POV 2.0 and onwards will rule the earth. 2.0 has a built in efficiency scheme, and while most of the other free ray tracers out there are still faster, this scheme at least brings POV into the same league. What will make POV the most popular free renderer is that there are a ton of utilities out there to support it [see Dan Farmer's article this issue]. One of the most significant is MORAY, a shareware modeling and scene composition program that's very nice (available only on the IBM PC).

Right now Rayshade has more features than POV and is faster, and there are some programs which output data in Rayshade format, so it's got many users. But Craig Kolb is a busy guy and there doesn't look to be any new version coming out soon. There will still be people out there using Rayshade for its speed and for its multiprocessing utilities (e.g. the separate Inetray utility runs Rayshade on a network of processors/machines). Rayshade will be just fine for many people. The "art" ray tracer from Australia has a slightly brighter future; it has many of the features of Rayshade, plus its developers have time to actively support it.

Radiance will still have its users, too - anyone dealing with lighting in a true physical sense will use this package. Unfortunately, Greg Ward tells me that the DOE (who funded the development of Radiance) may not release newer versions for free; keep your fingers crossed.

BRLCAD has its devoted users, but takes more work than just downloading to get (you must be a US citizen, you sign some agreement, etc etc). So even though it's free if you qualify, it's much more for the serious user and so has nil "hacker momentum".

There are some other free ray tracers out there (RTrace, VIVID/BOB, etc), each with some advantages, but in the main the large number of people using POV and creating utilities for it will make these others of peripheral interest in the long run. 90% of the utilities developed for POV might be clunky junk, but there will be enough hits (such as MORAY) that this renderer is made usable by the masses. Whether this is good or bad or whatever, well, I don't really know, but this is my current impression of the short-term future of free ray tracing software out there.

Anyway, this is an incredibly long issue, as I finally caught up with the backlog from March onwards. Given its length, I hope you'll take it all in (hey, use "split" and "at" and send yourself this issue in installments...). There's a summary of the features and speeds (in two separate articles) of most of the free ray tracers out there. I've also started listing new papers that might be overlooked (i.e. weren't in SIGGRAPH). Something for everyone, I hope (or if nothing else, at least all this stuff is organized so that I can find it again).

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New People

# J. Eric Townsend - massively parallel engines, vr
# NAS, NASA Ames
# M/S 258-6
# Moffett Field, CA 94035-1000
# 415.604.4311

I'm supposed to be administrating a CM-5, but I spend as much of my time as possible working on parallel ray tracers. My current project uses SEADS decomposition with cells distributed over the nodes. Cells are requested asynch and cached locally. Performance numbers coming soon.

What's the *biggest* thing you've ray traced so far in terms of sheer number of objects/size of database?

I'm (still) working on my massively parallel raytracer, but I've gotten official approval to work on it as part of my job, so I'm getting a lot done these days. One thing I've realized, is that I'll be able to trace some *huge* numbers of objects, or at least I think it's a large number...

Right now, an sphere+surface characteristics takes up about 512bytes of storage in my system (actually, any object takes up about that much space because the Object type is just a union of all the objects I support). Yes, that's a lot. I haven't tried optimizing for size yet. As I mucked about on our CM-5, I realized 'hey, I've got a *lot* of free ram for storage, even with a sizable local cache.'

Each node on our CM-5 has 2 banks of 16MB each. Assuming one bank is taken up with OS, code, object cache, data structures, generic BS, that leaves 16MB/node for permanent object storage. 16MB*32nodes (smallest partition one can grab)/512bytes/sphere==1M (1Kx1K, actually) spheres. Using all 128 nodes, I can easily have 4M spheres in my permanent object storage.

That's an awful lot, it seems to me. 4 million spheres is roughly equal to: - 568 sphereflakes(4) - 7 sphereflakes(6) - a single sphereflake(7) (5.3M spheres, actually).

Maybe it isn't a lot of objects. Regardless, I sat around trying to figure out how to use 4M spheres, and I came up with a few ideas:

 - particle methods run on another machine (when we get hippi going,
	we could run code on one machine and trace on another)
 - use spheres as voxels, try some volume ray tracing
 - bad abstract animation using too many spheres

Another probability is that'll I'll try some stuff with a 'special' object that has very simple parameters: position, pointer to an object definition and a pointer to a color index. That'd make it *quite* easy to get another few million objects floating about in the big database.

So, am I completely off my rocker?


Name:           Steven G. Blask
Fancy title:    Research Associate
But I'm really: PhD candidate/serf
		(will hack computer vision/graphics/image processing/AI
		 under UNIX/C(++)/X Windows environment for food)
Affiliation:    Robot Vision Laboratory
Snail-mail:     School of Electrical Engineering
		1285 Electrical Engineering Building
		Purdue University
		West Lafayette, IN 47907-1285
Voice:          (317) 494-3502
FAX:            (317) 494-6440
E-mail:         blask@ecn.purdue.edu

Interests: In short, I am doing my part to get ignorant computers to visually interpret their environment, initially for (but not limited to) robotic applications. Specifically, I am doing expectation-based image understanding, integrating a number of related research areas into a single unified system. I have created a B-rep solid model of the hallways outside our lab which is used as an internal map by our mobile robot. Based on where the robot thinks it is, an expected view of the environment is rendered via a (not-yet-so-)fast ray tracing algorithm which incorporates illumination effects.

While most rendering systems are focused on obtaining pretty pictures as quickly as possible, my application must also maintain links back to the underlying solid model so that, in addition to the appearance information, the 3D geometry and topology stored in the B-rep is efficiently made available to the scene interpretation process. This brings up many issues not normally addressed in the graphics literature which prevent me from taking advantage of some of their proposed speed-ups. However, it has caused me to re-examine some of the "solved" problems of computer graphics from a new perspective, which has yielded much dissertation fodder, and has allowed me to propose new speed-ups based on a slightly modified architecture.

Related non-graphics areas I have addressed include: low level image processing to remove noise from digitized images or enhance rendered images; robust segmentation and symbolic conversion of digitized greyscale video images and distance images produced by a range sensor; integration of these symbolic conversion routines into the solid modeler/sensor modeler/ray tracer which also has facilities for the interactive construction, examination, and modification of objects; an evidential reasoning scheme that organizes and utilizes the rich structural and appearance information in an efficient manner during the image understanding process. Artificial intelligence techniques such as evidence accumulation, uncertainty management, and symbolic reasoning must be utilized since there is a huge amount of input data and it will be noisy, the expectation will not be exact due to errors in mobile robot odometry (indeed, vision is intended to be its position updating mechanism), and it is impractical or impossible to completely or accurately model all of the environment and its many aspects. By processing both expected and observed scenes with the same greyscale or range image segmentation routines, the integrated system can predict the detectability of various structural features and appearance artifacts, and determine their usefulness w.r.t. the image interpretation process.

Obviously, I have taken a big bite out of a large apple, so please excuse me if I talk with my mouth full :-) I hope this tome makes the ray-tracing community more aware of the vast usefulness of this rendering paradigm to those who would do model-based interpretation of video and range sensor images. Ray tracing is a natural fit for my particular application since it tells me what object I hit, how far away it is, and what ``color'' it is. Computer vision & computer graphics are two sides of the same coin, and it is once again time to flip it over & see if the other guy has solved your problem yet. It is also probably time for the two communities to start working on an integrated modeling system that can drive the image formation/generation process both ways. I was forced to implement the aforementioned system myself since I could find no existing system that gave me the access I needed in order to efficiently integrate everything that needs to be done.

Sorry this is so long, but I thought you might find it interesting and possibly motivating. I encourage anyone interested in the further development of an integrated vision/graphics system to contact me. I am racing to defend my dissertation by December, so I may be slow to respond until then.

P.S. I am obliged to say that Purdue Robot Vision Lab is a diverse group of researchers investigating all aspects of sensory-based robotics, including: planning for sensing, robot motion, grasping, and assembly; object and sensor modeling; computer vision; image processing; range data processing; object recognition; symbolic and geometric reasoning; uncertainty management and evidence accumulation; learning. Smart, aware, easy-to-program robots are our goal. Prof. Avinash C. Kak is our fearless leader.

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Free Ray Tracer Summary, compiled by Eric Haines

Here are some of the better ray tracers out there (and most can be found at wuarchive.wustl.edu in graphics/graphics somewhere, or ask me):

RayShade - a great ray tracer for workstations on up, also for PC, Mac & Amiga. POV - son and successor to DKB trace, written by Compuservers. Also see PV3D. (For more questions call Drew Wells -- 73767.1244@compuserve.com or Dave Buck -- david_buck@carleton.ca) Radiance - see "Radiosity", below. A very physically based ray tracer. ART - ray tracer with a good range of surface types, part of VORT package. RTrace - Portugese ray tracer, does bicubic patches, CSG, 3D text, etc. etc. An MS-DOS version for use with DJGPP DOS extender (GO32) exists also, as well as a Mac port. VIVID2 - A shareware raytracer for PCs - binary only (286/287). Author: Stephen Coy (coy@ssc-vax.boeing.com). The 386/387 (no source) version is available to registered users (US$50) direct from the author. "Bob" is a subset of this ray tracer, source available only through disks in "Photorealism and Raytracing in C" by Christopher Watkins et al, M&T Books.

Which one's the best? Here's a ray tracer feature comparison of some of the more popular ones. I assume some basics, like each can run on a Unix workstation, can render a polygon, has point lights, highlighting, reflection & refraction, etc.

A "." means "no". Things in parentheses mean "no, but there's a workaround". For example, POV 1.0 has no efficiency scheme so takes forever on scenes with lots of objects, but there are programs which can generate efficiency structures for some POV objects (also, in this case, POV 2.0 will fix this deficiency).

		       Rayshade  POV 1.0  RTrace  Radiance     Bob       ART
IBM PC version?            Y        Y       Y      in 2.2       Y         Y
Amiga version?             Y        Y       .         Y         .        (Y)
Mac version?               Y        Y       Y       A/UX        .         Y

Sphere/Cylinder/Cone       Y        Y       Y         Y         Y         Y
Torus primitive            Y        Y       Y         .         .         Y
Spline surface prim.       .        Y       Y         .         .         Y
Arbitrary Algebraic prim.  .        Y       .         .         .         Y
Heightfield primitive      Y        Y       .         .         .         Y
Metaball primitive         Y        Y       .         .         .         Y
Modeling matrices          Y        Y       Y         .         .         Y
Constructive Solid Geo.    Y        Y       Y   (antimatter) (clipping)   Y
Efficiency scheme?       grids  (user/2.0) ABVH    octtree     ABVH    kdtree+

2D texture mapping         Y        Y       Y         Y         Y         Y
3D solid textures          Y      strong    Y         Y         Y         Y
Advanced local shading     .        Y       Y       Much!       .         .
Atmospheric effects        Y        Y       .         .         Y         Y
Radiosity effects          .        .       Y         Y         .         .
Soft shadows               Y      (2.0)     Y         Y         Y         Y
Motion blur                Y        .       .         .         .         .
Depth of field effects     Y        .       Y         .         Y         .
Stereo pair support        Y        .       Y         .         .         .
Advanced filter/sample	   Y        .       Y         Y         Y         .
Animation support          Y      (S/W)     Y      (some)       .         Y
Alpha channel output       Y        .       Y         .         .         Y

Modeler                 lib/P3D   IBM+  (convert)  on Mac    w/code      P3D
Model converters from     NFF     Many!   Many!     some        .      NFF,OFF
Network rendering       Inetray     .       .      in 2.2       .     dart,nart
User support           maillist maillist  good     digest+   little     good
Other S/W support        some     Much!   a bit     some      a bit     some

For timing comparisons, see the next article.

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Ray Tracer Races, Round 2, by Eric Haines

After running timings of the various ray tracers out there in the last issue, I received various comments from authors. David Hook and Bernie Kirby went so far as to run a bunch of the ray tracers on different platforms under different compiler options; see their results at the end of this issue. The POV developers sent me a beta of POVRAY 2.0 so that the snail's pace of 1.0 could be (massively) improved. Also, there were some interesting comments on how shadows for transmitters are computed; see the relevant articles on this topic. Without further ado, here are the current results.

Timings - default size SPD databases (i.e. up to 10,000 objects in a scene), time in seconds on HP 720 workstation, optimized and gprof profiled code. Includes time to read in the ASCII data file and set up. Note that profiling slows down the execution times, so real times would be somewhat faster in all cases (about 30%); plus, the profiler itself is good to +-10%. Also, these timings are purely for this machine - results will vary considerably depending on the platform (see David Hook's article). Now that I've explained why these are useless, here goes:

		balls   gears   mount   rings   teapot  tetra   tree

Art/Vort         478    1315     239     595      235     84     381
Art/Vort +float  415    1129     206     501      203     72     327
Rayshade w/tweak 188     360     174     364      145     61     163
Rayshade w/grid 1107     412     174     382      145     61    1915
Radiance         289     248     165     601      150     42     197
Bob              402     747     230     831      245     50     266
RTrace           664    1481     813    1343      341    153     372
RTrace c6 m0     652    1428     811    1301      331    155     363
POV 2.0beta+     588    1895     668    1113      306     56     542
POV 1.0        191000 1775000  409000  260000    45000  31000  250000

The gears and mount tests are probably worth ignoring because everyone handles shadows for transparent objects differently. Some consider them opaque to shadows, others handle it differently.

Here are timing ratios (i.e. 1 is the fastest time for a given test, with the other timings normalized to this value):

		balls   gears   mount   rings   teapot  tetra   tree

Art/Vort         2.54    5.30    1.45    1.63    1.62    2.00    2.34
Art/Vort +float  2.21    4.55    1.25    1.38    1.40    1.71    2.01
Rayshade w/tweak  1      1.45    1.05     1       1      1.45     1
Rayshade w/grid  5.89    1.66    1.05    1.05     1      1.45   11.75
Radiance         1.54     1       1      1.65    1.03     1      1.21
Bob              2.14    3.01    1.39    2.28    1.69    1.19    1.63
RTrace           3.53    5.97    4.93    3.69    2.35    3.64    2.28
RTrace c6 m0     3.47    5.76    4.92    3.57    2.28    3.69    2.23
POV 2.0beta+     3.13    7.64    4.05    3.06    2.11    1.33    3.33
POV 1.0       1015.96 7157.26 2478.79  714.29  310.34  738.10 1533.74

Art/Vort was compiled with and without a "+f" compiler option; with it on floating point numbers are not promoted to doubles during expression evaluation (and so things runs noticeably faster). Other packages may benefit from such compiler options.

Rayshade had some minor user intervention. The ceiling of the cube root of the number of objects in the scene was used as the efficiency grid resolution. For example, balls has 7382 objects: cube root is 19.47, ceiling is then 20, so a 20 x 20 x 20 grid was used. Rayshade needs hand tweaking of the grid structures for extra efficiency (esp. with balls and tree), though this is fairly simple for the SPD tests (i.e. leave the background polygon out of the grid structure). Tweaking in these cases means leaving ground plane polygon (if it exists) out of the grid structure.

Radiance is quite different in its approach, as it is more physically based. Efficiency structures are built in a separate program (so the time spent doing this is not included in the above stats). Also, Radiance outputs in a floating point format (which can be quite handy).

RTrace is often a bit faster when the "c6 m0" options are used.

POV 2.0 has an efficiency scheme built in and so is comparable to the others, so don't get freaked out by the POV 1.0 performance numbers.


Notes from Antonio Costa on RTrace:

Let me make just some small remarks about RTrace. Perhaps you haven't explored its options, but I think it could perform slightly better (at least 8% better, according to some simple tests I did).

Please run it with options 'c6 m0': c6 -> enclose at least 6 objects per enclosing box (default is c4) m0 -> use simple lighting model (default is m1, which uses a model developed by Paul Strauss of SGI; it's much more complex!)

When scenes have a larger amount of simple primitives like spheres and boxes the enclosing strategy isn't as efficient as when they have cones, patches, triangles, letters, etc. The value c4 is a compromise (normally the user shouldn't change it, but sometimes some tuning can be done).

[c6 turns out to be a bit better in most cases, but using both options improved performance by at most 4% maximum on my machine. -EAH]

The Strauss' model uses some math functions that unfortunately make the rendering somewhat slower then the standard Phong model (this is an area where I think good improvements can be done -- approximating functions like power(), sqrt(), acos()).

You can also avoid the problem with the 'rings' scene using an option that increases the number of surfaces -- option '+S2000' means 2000 surfaces (default is 256). To increase the number of objects or lights you can also use '+Sn' or '+Ln'.


For those of you who want to know the particulars of the tests, read on:

Here are the command lines I used for the various tracers. I tried to use the fastest method available for shadows for transparent objects - each tracer does this a bit different. Mostly I would say "ignore the results for gears and mount" because of the way the methods differ. I used the enhanced Standard Procedural Database package (next article) to test the ray tracers.

POV: time povray +ms5000 +i$dog.pov +ft +w1 +h1 -odummy.tga
ART: time art $dog.art 512 512
RAYSHADE: time rayshade $dog.ray -o -R 512 512 -O $dog.rle
RTRACE: time rtrace c6 m0 +S2000 w512 h512 O1 $dog.rt $dog.ppm
	sed -f vivid2bob.sed $dog.b > /tmp/junk
	mv /tmp/junk $dog.b
	time bob -s $dog
	# uses a converter Greg Ward sent, which I call NFF2Radiance
	../../$dog -r 1 | NFF2Radiance -vf $dog.vp > $dog.rad
	oconv $dog.rad > test.oct
	time rpict -vf $dog.vp test.oct > $dog.pic

[Addendum: more timings are available from Andrew Woo in RTNv10n3]

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An Enhanced Standard Procedural Databases Package, by Eric Haines

Alexander Enzmann and Eduard Schwan took the SPD package (which, as you may know, generates procedural models for testing ray tracer speed) and added a ton of code to it. The new code now outputs to these formats:

	NFF (used by MTV ray tracer; but the SPD always output using this)
	POV-Ray 1.0
	Polyray v1.4, v1.5
	Vivid 2.0
	RTrace 8.0.0
	Art 2.3
	QRT 1.5
	POV-Ray 2.0 (no, it's not officially out yet: format subject to change)
	PLG format for use with "rend386"
	Raw triangle output

It can also output the models as line drawings to the screen for previewing: IBM, Mac, and HPUX drivers are provided, and new drivers are trivial to write (i.e. draw a line).

There is also a program, showdxf, which will convert or display DXF files (actually, a limited subset of these - just 3DFACE entities). There are two sample DXF files, a skull and an f117, included.

There's also a sample code file which can be used as a template for writing your own output programs. What's nice about this package is that by writing a program representing your model (or interpreting your model as input a la showdxf.c), you can then convert it to a wide number of formats. I'd love to see more show*.c interpreters (e.g. one for Wavefront obj format so that the cool Viewpoint models at avalon.chinalake.navy.mil can be converted) and other output formats.

I did some polishing and whatnot to the distribution and have placed the whole thing at weedeater.math.yale.edu's /incoming directory as SPDup31.tar.Z and SPDup31.zip . Hopefully I didn't futz things too badly (I suspect there needs to be some file renaming for the Mac version), but let me know if I did. Anyway, I hope that the permanent home of the code will be princeton.edu:/pub/Graphics somewhere.

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Shadows from Refractive Objects, by Steven Collins (steve@crl.hitachi.co.jp)

gophcide@cs.montana.edu (Brett Donahue) writes:
>After tracing a ray from the view plane and hitting an objects surface, you
>cast a ray from that point to the light source. What do you do if there is
>a total transparent object with an index of refraction on the path to the
>light source? Once this ray is refracted, it will not hit the light source.
>Do you just ignore the object? That is what I think POV ray is doing. I
>put a transparent object between a plane and the light source; and there
>was no shadowed areas. There should be some areas on the plane where the
>refracted light would not hit.

A moot point indeed. Not many ray-tracers handle this problem correctly. Most take the "easy way out" of either a) ignoring the ray if _any_ obstacle is encountered between the surface and the lightsource or b) if the ray passes through transparent objects only, then attenuate the lighting according to some scattering approximation function. a) always gives rise to completely dark shadows, whereas b) is an improvement in that it gives rise to lighter regions of shadow where the light has been attenuated proportional to the distance of refractive material passed through.

Either of these approaches do not capture the caustics effects. There seems to be 2 methods around to do this: either a) send out _lots_ of rays from the surface in the hope that some of them will hit the light source. i.e.: sample the hemisphere above the point of intersection and trace these rays. For better results the hemi-sphere may be importance sampled by determining the solid angle subtended by all light sources. This is of course incredibly expensive computationally and leads to very noisy caustic effects. The alternative approach is to shoot rays from the light sources in a pre- processing step. A number of approaches to this exist. Heckbert proposed shooting may rays from the light sources and storing the intersections of these rays with surfaces as a "texture map" of sorts. Thus when executing the secondary phase, intersections with surfaces use these texture maps as an estimate of the light incident on the surface. Another approach is that of Watt & Watt where a beam tracing first phase performs a similar operation but this time only polygonally defined surfaces are catered for (due to the beam-tracing approach). Here, light beams are traced through the scene and the intersections of these beams with surfaces are stored as polygon feature polygons and used in the "eye-phase" to estimate the caustic light energy. Finally, more recent work (I've just shipped my Siggraph '92 procs. over 3,000 miles away so forgive not being able to give the exact reference) published in Siggraph '92 (was it Kirk and Barr or Snyder...? or Arvo... these guys do so much excellent stuff its hard to keep track) [no, it was Mitchell and Hanrahan -EAH], which involved a more analytic approach to determine the location of the caustic effects by analytically estimating the wave-fronts and caustic cusps resulting from light interacting with a surface of gaussian curvature.

This is, as you can probably guess, an area of interesting on-going research.

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Shadows Through Transmitters, by Eric Haines, Greg Ward, Alexander Enzmann, Stephen Coy, and David Hook

In doing the SPD timings tests on the various ray tracers available, I found that each renderer does shadowing of transmitters its own way. This is fair enough: when a transmitter "blocks" a light, there are many ways to handle the situation. One is to treat the transmitter as opaque and simply block any light. Another is to filter the color of the light by the transmitter's surface color. A more elaborate method is to actually compute the length of the ray inside the transmitter and then also attenuate the color using this distance (e.g. Radiance does this). For my tests I tried to pick the fastest option available with the ray tracer.

Some comments from the designers:


From Greg Ward (the main author of Radiance):

As for the shadow under a refracting sphere or such, I just follow the rays through the object to the light source following a refracted path, and if I hit it, I get it, if I don't, I don't. It's not the correct thing to do, but it's better than throwing the contribution away or pretending it's not there, and it does give the appearance of light concentration in some cases. To be honest, I don't care that much about refracting objects as they rarely turn up in architectural scenes. Windows, yes -- crystal balls, no.

Yes, the refracted path source testing depends on the size of the light source among other things, so it's not a correct approach (as I said). But it's easy, and strikes me as better than nothing. I don't do any special type of sampling with regards to ray direction -- I just shoot assuming that there's nothing in the way, and if I hit a dielectric surface, I continue to follow the refracted (but not the reflected) ray. Works great for planar surfaces, so it makes most of my users happy.


From Alexander Enzmann (an author of POV-Ray):

Another thing to consider with POV-Ray (especially in gears) is that diffuse shadows are computed for all surfaces. Several tracers have an option for how many surfaces will have shadows computed (Rayshade and RTrace have several options), some tracers don't ever compute shadows for an "interior" surface of a transparent object (Vivid/BOB). POV-Ray always does the maximum work. The high ratio you got on the gears benchmark comes from that to a great extent and from the fact that POV-Ray doesn't do polygons (has to have the gears broken down into triangles).


From Stephen Coy (an author of the Vivid/Bob ray tracers):

There actually seem to be two issues here. The first is how the intersection with an "interior" surface is shaded. The second is how shadow colors are calculated.

When Vivid/Bob intersects an interior surface the only component that is taken into account is the transparency. This implies that the surface doesn't have a diffuse component (hence no shadows), it doesn't have a specular highlight and there are no reflected rays generated. I've come to believe that my handling of the specular rays and highlights is wrong. As far as the diffuse component goes I think the correct solution is quite a bit tougher. I think that the proper solution would involve the effects of the light all along the ray as it passes through the transparent material. In effect, transparent materials should be treated like participating media where you actually have a diffuse contribution and shadows cast throughout the volume.

When it comes to calculating the color of shadows Vivid/Bob gives you a couple of options. With the no_exp_trans flag set, the light color is simply filtered by the transparent component of the material. When this flag is not set (the default) the amount of the filtering is attenuated exponentially based on the distance the ray travels through the material. Note that this has the side-effect of making the material definition scale dependent. Additionally Vivid/Bob also supports fake caustics. For these, the color of the shadow ray is further tweaked based on the angle between the surface normal and the direction of the shadow ray. This was inspired by Andrew Pearce's trick in Graphics Gems I.


From David Hook (an author of the "art" ray tracer):

Art traces the ray straight through the object checking for texturing and modifying the light passed through accordingly. Apart from the texturing it doesn't seem to cause to much heartache computationally, although, as Greg Ward points out, going straight through without taking into account effects due to refraction fails to produce any caustics, which are the things that make refractive light the most interesting. On the satisfaction-with-the-image side, we have another program using the same shading model that is used by architects, and the lack of caustics has never caused any problems. I sometimes wonder if computer graphics people are the only ones who notice them!

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Faster Bounding Volume Hierarchies, by Brian Smits (bes@graphics.cornell.edu) and Eric Haines

[I'm writing up this idea that Brian passed on to me. It turns out to be quite old, mentioned in Goldsmith's article and in Arvo & Kirk's section of _An Introduction to Ray Tracing_. For whatever reason, I didn't know about it until Brian filled me in (guess I should read things a bit more carefully!). I haven't seen the idea applied to Kay & Kajiya's scheme, nor have I seen any test data about it or seen it used in any free ray tracing software. It's pretty trivial to implement, so I recommend it. -EAH]

This article presents a simple way to improve the performance of automatic bounding volume hierarchy schemes. Automatic bounding volume hierarchy methods are one way to improve the efficiency of ray tracing. By putting objects in a nested hierarchy of bounding boxes and testing each ray against these, most of the objects in a scene can be quickly rejected as not intersecting the ray. Goldsmith/Salmon & Scherson/Caspary explored methods of building up a hierarchy of bounding volumes automatically, as did Kay/Kajiya.

Kay & Kajiya simply built a hierarchy of boxes by sorting the object set by the object centroid locations in X, then Y, then Z. For example, with a hundred objects in a scene the objects' 3D center points would be sorted by X, and then this sorted list would be split into two sublists of fifty objects each, with a box put around each list. Each sublist in turn would be sorted by their Y centroid values and split into two subboxes with twenty-five objects each, on down until boxes with two objects are created at the bottom of the hierarchy.

Goldsmith & Salmon wished to group objects more tightly. Splitting a list of objects may not be such a great strategy: imagine that of our hundred objects, fifty one made up a light fixture and forty nine made up a stapler that the light shines upon. Splitting into two groups of fifty means that one box will include all of the stapler and one piece of the light, and so giving a box which contains a large amount of empty area between the light and the stapler. A tighter bound, e.g. having a box around the stapler and another around the light, would yield better timings. Goldsmith & Salmon's strategy is to randomize the list of objects and feed these into a hierarchy, placing each new object in the hierarchy so as to minimize the overall growth in size of the boxes in the tree. By randomizing the list the first few primitives will tend to create a "skeleton" upon which the rest of the primitives can efficiently become a part. [See the RTNews2 file at princeton.edu for more information.]

Brian Smits implemented this scheme in his ray tracer, and Jim Arvo pointed out a simple speed up (mentioned in Goldsmith's article). By trying different randomized lists, various different configurations of the hierarchy occur. These hierarchies can be analyzed by examining their efficiency. The criterion Brian used is the internal cost of the root node (see p. 212 of _An Intro to RT_). Another simple criterion is to sum up the areas of all of the bounding volumes. Each configuration will generate a different value; using the hierarchy with the best value will generally improve performance, since fewer bounding volumes should be intersected overall. So time can be saved overall by spending a little extra time up front generating a few different configurations using different random number seeds. The best random number seed can be saved for a particular scene and reused later to generate this best hierarchy. This is quite a nice thing for fly through animations in particular: one can spend a lot of time up front getting a good hierarchy and then store just one number (the seed) for the best efficiency scheme for the scene.

Brian notes: "I found that on some environments that a good hierarchy could take half to a third of the time of a bad hierarchy. `Average' hierarchies tended to be closer to good hierarchies than bad hierarchies, though."


(Eric Haines) I have a few comments:

This same idea could be used on Kay and Kajiya. Which axis is sorted first, and which order the axes are sorted (e.g. XYZ or XZY), gives six different generation combinations when using Kay and Kajiya. By examining the fitness criterion of the boxes generated for each of these six, the tightest of the six can then be used.

I have a copy of POV 2.0beta sitting around which does Kay/Kajiya, so I hacked it to try the various combinations. POV 2.0beta actually uses a different scheme than pure Kay/Kajiya: it sorts each box along the longest axis. For example, if you had 8 spheres in a row along the Z axis, it would come up (reasonably enough) with a hierarchy with each box's contents sorted along the Z axis.

Timings for Kay/Kajiya:

	balls   gears   mount   rings   teapot  tetra   tree     shells

longest  588    1895     668    1113      306     56     542      1464
  area:    5214   881      205    30995     1514    74     74548    604068

XYZ      513-   2019     639+   1158+     288+    54-    516      1661-
  area:    4420-  938      195    29174+    1367    72     74361+   688388
YZX      512    2316-    644    1188      292     52     531      1605
  area:    4399  1071-     211    29944     1343    72     74402    686440
ZXY      513-   1735+    659-   1215-     298     52     549      1554+
  area:    4388   764+     233-   30936-    1334    72     85085-   649846+
YXZ      507+   1916     656    1182      301-    52     514+     1658
  area:    4420-  884      190+   29583     1456-   72     74557    696927-
ZYX      513-   2006     658    1183      289     52     532      1572
  area:    4385+  869      226    30254     1321+   72     74382    651506
XZY      508    1892     642    1187      293     52     552-     1579
  area:    4402   910      215    30066     1373    72     74616    673416

"longest" is the "sort on the longest axis" scheme which comes with POV 2.0. "XYZ" means sort on the topmost level along X, then the subboxes along Y, then Z, etc. The lowest value in a column (among the simple orderings) and category is marked with "+", the highest with "-".

As Brian notes, there's usually one bad hierarchy among the lot next to a bunch of reasonable ones. There is some correlation between the area summation and the resulting rendering time: "gears", in particular, has significantly different results and the best area summation is 1.33 times as fast as the worst (and the area of the best is 1.4 times smaller than the worst). Most of the models have a fair bit of similarity along each axis. Tetra's symmetry is a great example: the axes' order just does not matter. Gears does not, and so different schemes have significantly different results. Using more realistic scenes would be interesting and probably give larger variances in results.

What's also interesting is that many of the simple XYZXYZ orderings beat the "pick the longest axis" method in overall timing. In the "mount" and "shells" models the longest axis method is always better (in both timing and area summation), and in the "balls" and "teapot" models the longest axis is always the worst strategy.

Another scheme which deserves exploration is to sort on each axis, XYZ, and compare results: using the axis which creates two boxes with the smallest total area would be an interesting strategy which should give fairly low area summations overall.

I suspect there is also not much difference between schemes because of the nature of the databases: there's usually one object cluster instead of a few objects separated by distances (as would occur in a room, say), so the different schemes don't make too much difference. I would also suspect wider variations when using Goldsmith/Salmon, as there is a lot more randomness and opportunity to seriously improve (or degrade) performance. As it stands, for these models doing multiple hierarchies for Kay/Kajiya and picking the best doesn't save much time (maybe 4% on average) - kind of disappointing. Using the absolutely longest axis doesn't seem to be a win for these scenes, though for other less homogeneous scenes it might perform better. I don't know why it performs consistently worse for some databases; if nothing else, it does show that intuition is not always a good guide when designing new efficiency schemes.

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Simple Sun Position Program, by James Ashton (jaa101@deakin.anu.edu.au)

Guy Carpenter asks:
>I'd like to be able to specify lon, lat, elev, date, time and get an
>accurate position for the sun, and position, phase and orientation for
>the moon. I think I have all the necessary alg's kicking around, so it
>shouldn't be too hard.
>- has anyone already done this?

I haven't done it very accurately but I did scrape together a quick and dirty Sun position generator in C. It's only a rough approximation with no attempt to model the equation of time or lesser effects. You provide latitude (in degrees), month (Jan 0th = 1.0, Dec 15th = 12.5, etc) and local time of day (midnight = 0.0, midday = 12.0) and it gives the (x, y, z) coordinates for a rayshade light source direction. Z is up but I forget which axis I made North. It was designed to aid in designing a `Solar house' and I'm sure it's accurate enough for that purpose. It's a model of inefficiency but who cares!


#define DTOR(d) ((d) * M_PI / 180.0)
#define SEASON_ANGLE(month) (sin(((month) - 9.7) / 6 * M_PI) * 0.41)
#define HOUR_ANGLE(hour) ((hour) / -12 * M_PI)
#define POSITION_ANGLE(latitude) (DTOR(latitude))

double latitude, month, hour;

	double x, y, z;

	for (;;)
		if (scanf(" %lf %lf %lf", &latitude, &month, &hour) != 3)
			fprintf(stderr, "bad floats read\n");
		x = (-cos(SEASON_ANGLE(month)) * sin(HOUR_ANGLE(hour))),
		y = (-sin(SEASON_ANGLE(month)) * cos(POSITION_ANGLE(latitude)) +
		    cos(SEASON_ANGLE(month)) * cos(HOUR_ANGLE(hour)) *
		z = (-sin(SEASON_ANGLE(month)) * sin(POSITION_ANGLE(latitude)) -
		    cos(SEASON_ANGLE(month)) * cos(HOUR_ANGLE(hour)) *
		printf("%f\t%f\t\t%f\n", x, y, z);

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Sphere and Cylinder/Cone/Disc/Annulus Definition, by Eric Haines

Jonathan Roy asked me what I liked for quadric definitions. I worked on this question professionally a few years back, and thought I'd pass on what I found.

I like for a sphere:

	radius, origin, axis for north pole, axis for start point on equator
		(and optionally right or left-handedness)

The axes are important when you're applying a texture to a surface (otherwise can be ignored). Of course, the user doesn't have to see it this way. For defining ellipsoids, no one bothers with defining the foci - you simply need to non-uniformly scale (e.g. stretch) a sphere with a transformation matrix. You have to be sure to stretch the normal equation for the sphere by the transpose of the adjoint of this matrix to get the normals right (see An Intro to Ray Tracing in Pat Hanrahan's section for a little more on this, and see old issues of this newsletter).

I like for cylinders/cones/annuli (i.e. "washers"):

	base origin, axis vector, base radius, apex radius, height, axis for
		starting texture point on equator

This is real general and gives you three different primitives all in one. In the code you will probably want separate intersectors for them, though (i.e. height of 0.0 means it's a washer and the cone equation will tend to explode at this height).

back to contents

Ray Tracing Roundup

Watt & Watt's book, _Advanced Rendering and Animation Techniques: Theory and Practice_, is a good unified guide to advanced rendering in general and I highly recommend it. Think of it as a condensed and simplified "Best of SIGGRAPH" for the past decade and you won't be too far wrong. (Eric Haines)


The 3rd edition of the cross-indexed bibliography on ray-tracing and related topics is available. Included in this edition will be some 600 citations, papers from all the major graphics conferences and full keywording of citations. Cross-reference files (by keyword and author) and a glossary of the 120 keywords used are also slated for inclusion. (Rick Speer, speer@cs.colorado.edu)


Texture Library Site

The beginning of a texture library for rendering applications is being started on wuarchive.wustl.edu located in the mirrors/architec

directory. Please FTP the README file first. There are around 100 texture images stored in compressed TIFF format. (Paul David Bourke, pdbourke@ccu1.aukuni.ac.nz)

[I looked at the initial 40 of these. Good idea, but only a very few of them were tileable (i.e. could be repeated seamlessly over a surface). -EAH]


Inventor 3D File Format, by Gavin Bell (gavin@sgi.com)

You can do a great service to everybody if you avoid creating yet another 3D object file format and at least adopt Inventor's ASCII file format for your system. If not the objects, at least the syntax, to make translation easy. Documentation on the file format is free-- you can anonymously ftp it from sgi.com:sgi/inventor/Doc.tar.Z.


Ray Traced Church Interiors

There is a series of five images of the interior of the Renaissance church "Il Redentore" in Venice. The original (huge) Utah RLE images are available from: cad0.arch.unsw.edu.au:/pub/rayshade/images/Il_Redentore

The images were produced using Rayshade, the images and the model were created by Nathan O'Brien as part of his undergraduate dissertation "Building Preservation and Three Dimensional Computer Modelling" at UNSW.

These images are extremely good IMHO, and well worth the effort of getting! (Stephen Peter, steve@keystone.arch.unsw.edu.au)


You may ftp jpeg versions of them (perhaps for a limited time only) from: services.more.net (Columbia, Missouri, USA) in /pub/jpg/Il_Redentore.

These are not the jpegs which appeared on alt.binaries.whatever but were jpegs recreated from the original .rle files by me. (David Drum, UC512052@mizzou1.missouri.edu)


My book is coming out in October and is called "Adventures in Raytracing," published by QUE. It covers Polyray from "top to bottom". The book is dedicated to raytracing (with Polyray), 3d modeling (with POVCAD - my program) and animation. The book has an almost complete reference on Polyray and it even includes a tear-out card with the command lines, language syntax, etc. It includes a disk with Polyray 386 (no 387) and 386/486 (+387) version, POVCAD (windows and Dos version) and CompuShow (image file viewer utility).

Right now I've also written a small utility called CLAY.ZIP which does free form deformation on RAW data files. The output comes out as RAW also. In addition I've written another utility to tween 2 RAW data files in Polyray - the good thing about it is that it can do linear, quadratic or cubic interpolation... and the output from the utility is just 1 file independently of how many frames are required. (Alfonso Hermida, afanh@stdvax.gsfc.nasa.gov)


I've just completed a book on 3D graphics animation with Dave Mason called "Making Movies on Your PC". Lots of pretty pictures, mostly beginners tips on creating FLI/FLC format animations on IBM clones. (Alexander Enzmann, 70323.2461@compuserve.com)

[This book also includes Polyray and 2D morphing software. -EAH]


YART 0.40 - a Fast Growing Framework for Obj.Or.Graphics, Ekkehard Beier (ekki@prakinf.tu-ilmenau.de)

The time is good for a new graphics system, including both ray-tracing and gouraud shading facilities! This system should be object-oriented, highly extensible and highly interactive (Real-time raytracing or real-time shading and raytracing if explicitly wanted). Using SGI GL/PHIGS[PEX]...-shading for built-in modelling and direct interaction, and Raytracer for HiQuality final images.

	* YART - Yet Another Ray Tracer *

is a first implementation of such a system.

*there is a mailing list: yart@prakinf.tu-ilmenau.de

*PLATFORMS: SGI Iris, SUN Sparc, Linux-PC, [MS Windows - in work]

ftp from metallica.prakinf.tu-ilmenau.de [] : pub/PROJECTS (login as "ftp", password "HARLEY FUCKIN' DAVIDSON").

*PRECONDITIONS: C++ (At&T cfront 2.1), Tcl, GL or X11 or PHIGS PLUS.

[There's lots more text, contact the author for more info. -EAH]


General software:

3DS2POV is a utility that converts 3D Studio files to POV-Ray, Vivid, Polyray, or raw triangle formats. A bounding volume hierarchy is added to the POV-Ray files. The latest version converts from the binary .3DS format where previous versions used the ascii format. If you've got the time (or a Cray) it'll convert whole animation sequences as well. This program is on the YCCMR BBS and the TGA BBS as 3DSPOV17.ZIP. Both DOS binaries and C source are included. (Steve Anger, 70714.3113@CompuServe.COM)


[I haven't mentioned BRLCAD for awhile, so here's a blurb:]

The US Army BRLCAD package (brl@cad.mil) -- Ballistic Research Laboratory is available as encrypted source code via anonymous ftp from: ftp.brl.mil:/brl-cad/* FAX a completed copy of the 'agreement' file to BRL for the 'crypt' key. BRLCAD is very mature -- also runs in parallel on a heterogeneous mixture of systems -- image quality is good -- but perhaps not extraordinary. (Alexander-James Annala)

[It really does look like an amazing system, worth checking out if you plan on doing any "serious" modeling, esp. CAD related. - EAH]


Radiance related:

A fellow by the name of Georg Mischler of ETH in Zurich, Switzerland, has written a new translator for exporting Radiance files from within AutoCAD. This new AutoLISP program seems to be quite capable, and he has installed it in the pub/translators directory on the anonymous ftp account of hobbes.lbl.gov ( I invite users with AutoCAD to try it out. (Gregory J. Ward, greg@hobbes.lbl.gov)


Rayshade related:

I have just compiled the 'Enhanced' version of Rayshade (patchlevel 6) for a PC running MSDOS and it appears work fine. You can get it from telva.ccu.uniovi.es ( /pub/graphics/raytrace/rayshade/MSDOS/Erayshade.for.PC.zip. You'll need a 486 ( yeah, you'll can run it on a 386, but S...L...O...W ). Also I packed a shower and a converter from/to the RLE file format. (Raul y Quique, nuevos%hp400.ccu.uniovi.es@Princeton.EDU)


I am placing in weedeater.math.yale.edu:/incoming 3 executables: getX11, rayshade.4.0.6, raypaint.4.0.6 which have been ported to SCO UNIX & Univel SVR. They will run in both environments.

These have been optimized for INTEL 486 & Pentium processors to use on-chip FPU & cache memory. (Robert Walsh, SCO (robertwa@sco.com))


I have just uploaded a port of rayshade 4.0.6enh2 to OS/2 2.1 to weedeater.math.yale.edu. Most of the patches posted through July 20, 1993 to this list have been added. (David C. Browne, DBROWNE@diamond.kbsi.com)


Check out the June issue of Omni Magazine, page 52.

The "computer-generated image of HIV created on a Cray Super Computer" was done with Rayshade. It really looks much larger in person :-):-). A larger version of this image may be found on:


in tmp/rayshade as virion.rle.Z. For more info you can contact me at mcgregor@ncifcrf.gov or Connor McGrath at mcgrath@ncifcrf.gov. (Please see the acknowledgment.txt file for a few more details).


RTrace/Radiosity related:

The "lightR" radiosity program from Bernard Kwok (ae140@freenet.carleton.ca) is now available to run in a PC with DOS DJGPP GO32 extender. You can ftp a working version with some scenes and utils at asterix.inescn.pt [] in directory pub/LightR/PC-386 (lightr12.arj) The source code is in pub/LightR/PC-386/src (lightr.arj) I found the program very interesting and it helped me to learn a lot about Radiosity (a rendering algorithm). I have also adapted its output to the RTrace ray tracer so that nice images could be produced:

	     lightr          scn2sff         rtrace
   PAT, VW ----------> SCN ----------> SFF ----------> PIC PPM

I included minimal docs and specs, but I intend to improve this area in the future... Please feel free to contact me. (Antonio Costa, acc@asterix.inescn.pt)


There is a new version of the RTrace ray-tracing package (8.3.2) at asterix.inescn.pt [] in directory pub/RTrace. Check the README file.

RTrace now can use the SUIT toolkit to have a nice user interface. Compile it with -DSUIT or modify the Makefile. SUIT is available at suit@uvacs.cs.virginia.edu


I have put in pub/RTrace here 2 PostScript docs describing the syntax of both SFF and SCN. I would many people to read them and send me comments, if possible... The files are sffv8-p?.ps.Z and scn15-p?.ps.Z (Antonio Costa, acc@asterix.inescn.pt)

[There are undoubtedly a large number of other changes and additions to RTrace by this time; Antonio seems to have unlimited time and energy for this thing! For example, I noticed he now has an IRIS Inventor input interpreter. Check with him for the latest. -EAH]


Vivid/Bob related:

Triangular Glob Generator v1.0
copyright 1993, Dov Sherman

(For use with Stephen Coy's Vivid Raytracer v1.0 or higher)

GLOB is a handy utility for creating more realistic, rounded objects without relying on bezier patches (which are still good but hard to work out on paper).

GLOB takes an ASCii file containing the coordinates and radii of a series of spheres and creates smooth connections between each sequential pair, connecting the first and third spheres in each sequential triple, and placing a triangular polygon over the gap created by a sequential triple. I'll try to explain this better later.

The output is in the form of an include file for Stephen Coy's Vivid Raytracer. Other raytracer formats may be supported in future versions if I ever manage to figure out the other ones.

GLOB10.ZIP is available from wuarchive.wustl.edu. I just put it in /pub/MSDOS_UPLOADS/graphics. Also available on the You Can Call Me Ray BBS.



POV related:

Ray Tracing Creations
Drew Wells, Chris Young, Dan Farmer
The Waite Group
ISBN 1-878739-27-1

This book covers the POV ray tracer from soup to nuts, with lots of examples and whatnot. Essentially, it's a users manual for POV, and it comes with POV 1.0 on disk. (Eric Haines)


There's a new GUI modeller call MORAY out for POV-Ray. This is the most complete modeller for POV-Ray I've seen so far. It supports most of POV-Ray's primitives, CSG, hierarchical linking, and has an nice bezier patch editor. Here's a short description from the docs:

MORAY V1.3 is an easy-to-use GUI modeller for use with POV-Ray 1.0 (and 2.0 when released). It supports the cube, sphere, cylinder, torus, cone, heightfield and bezier patch primitive, as well as adding conic, rotational and translational sweeps. You can add (spot)lights, bounding boxes, textures and cameras, which show the scene in wireframe 3D. Shareware US$59. Not crippled. Requires 286 or higher, mouse, runs on VGA and SVGA/VESA.

MORAY version 1.3 is available at ftp.informatik.uni-oldenburg.de in /pub/dkbtrace/incoming. (Steve Anger, 70714.3113@CompuServe.COM)


No, POV 2.0 is not out yet. To whet your appetite:

POV 2.0 includes automatic bounding boxes, better textures, recursive antialiasing, primitives for finite cylinders & cones. The parser will now accept mathematical expressions for vectors and floating point numbers. It also has some bugfixes.


When using PoV on a X window based Unix system as f.i. Linux, you may use my x256q Previewer code instead of the xwindows code that comes with PoV.

It resides on irz301.inf.tu-dresden.de:pub/gfx/ray/misc/x256q (Andre Beck, beck@irzr17.inf.tu-dresden.de)


Check out the 3d l-system generator (ms-dos) for POV-Ray raytracer I found on the graphics alternative bbs 510-524-2780. the qbasic source makes a raw coordinate file for input to raw2pov for smooth_triangle output. 3 examples from 'algorithmic beauty of plants' provides about 8 variables that one can fuss with to produce diff shape trees/bushes. uploaded as treebas.zip to ftp.informatik.uni-oldenburg.de:pub/dkbtrace/incoming/ (mirrored on wuarchive.wustl.edu:graphics/graphics/mirrors/ftp.infor...) (Tony Audas, taudas@umcc.umcc.umich.edu)


I use POVRAY and the small Makeanim program to do animation - using makeanim you create a file with a series of movement variables - and it #defines them into the .pov code and raytraces them all in sequence. So if you want a camera pan diagonally upward, your .anm file should look like: pan_x, pan_y 0, 0 1, 1 2, 2 etc... It will define these for you, and they should be used instead of x and y in your camera definition. Makanim will only handle 20 variables, unfortunately, so you can really only make 20 or less things move - but if you move the camera around, this can make up for things. (Dane Jasper, dane@nermal.santarosa.edu)


RAW2POV is a utility that converts triangle data listed in xyz triplets to POV-Ray smooth triangles. It automatically adds its own bounding volume hierarchy to overcome POV-Ray's lack of an efficiency scheme. This program is on the YCCMR BBS and the TGA BBS as RAWPOV17.ZIP. Both DOS binaries and C source are included. [Also see 3DSPOV writeup above] (Steve Anger, 70714.3113@CompuServe.COM)


If you have any comments or suggestions about POVCAD please let me know. The home of POVCAD is Pi Square BBS (301)725-9080 in Maryland USA. You may download POVCAD (DOS or Windows version) and get the latest info on it. [POVCAD is up to version 2.0b for Windows by now, and has more features than the non-Windows version); there are also rumors that an X-Windows version may be forthcoming. -EAH] (Alfonso Hermida, afanh@stdvax.gsfc.nasa.gov)


A lot of developers (A. Hermida, Lutz Kretschmar, Dan Farmer, Stephen Coy) also hang out the PCG (Professional CAD Graphics Net). You can get access to this net via the BBS'es mentioned in the PoV docs, and in Europe via BBS Bennekom, fido node 2:281/283, telephone 31-8389-15331. Using Bluewave, I can read and write in the echos for free. (Han-Wen Nienhuys, hanwen@STACK.URC.TUE.NL)


In the PC world, I have use a program called VVFONT. It uses the stroke fonts in borland and produces the characters as unions of spheres, codes, planes, boxes, cylinders, etc. It produces very good results and allows for rounded, block, and beveled format for POV, DKB, and Vivid ray tracers. If I don't see it on the net, I will check with the author and download it somewhere and post the location if there is any interest shown. (Mike Hoyes, hoyes@rock.concert.net)


I've uploaded my (uppercase only) alphabet to ftp.informatik.uni-oldenburg.de:pub/dkbtrace/incoming (or some such place... you know the one I mean). The letters consists of cylinders and torii, suitably bounded for performance reasons. There is also a utility for writing strings, and two sample .pov files. Oh yes, almost forgot. The file is called 'beta.zip' (as there is already an alpha.zip... Imaginative, huh?) (Reidar "Radar" Husmo, radar@cs.keele.ac.uk)


There are a few other ways to render text. Look in ftp.informatik.uni-oldenburg.de: pub/dkbtrace, there are two alphabet pov files, alpha.zip and beta.zip, examples of using pov shape_types in creating 3D text. Another way I can think of is to use the connect-the-dots utility to create letters. Further possibilities include using Vision 3D's extruder to extrude the text and output DXF, then convert to pov triangles. A third method I think may work is to use Paul Bourke's "BitSurface" utility which converts bit-maps to DXF, and again convert to pov. (Helmut Dotzlaw, dotzlaw@CCU.UMANITOBA.CA)


I produce fonts for PoV commercially [see RTNv6n2 for more info. -EAH]. For a demo, and some sample letters, have a look in ftp.informatik.uni-oldenburg.de pub/dkbtrace/incoming or pub/dkbtrace/utils for some of these:

avantest.zip    38988  21/10/92   5:14
fntbench.zip    33628  21/02/93  17:25
fntsamp.zip    132164  23/07/93   5:58
tms_rom.jpg     27560  21/02/93  17:28

Kirk2.jpg illustrates the use of the fonts in a more professional capacity. (Andrew Haveland-Robinson, andy@OSEA.DEMON.CO.UK)


One of the best utilties I've found for POV is called SP - Dave's Spline- Path Generator. You can find this on the You Can Call Me Ray BBS. Basically, you make a data file of a number of points and some other information, and SP will calculate position and rotations for your camera. You can do acceleration/deceleration, etc... with it as well. Its downfall (at least as of version 0.3) is that it only does one frame at a time (you tell it which of the N frames to compute). It's relatively easy to make a batch file for this, though. (Jason Barile, barilejb@ctrvax.vanderbilt.edu)


A good many of the utilities for POV-Ray have been designed to use what we call ".raw" format (bare vertex data) which can be bound very tightly in a hierarchical structure of bounding boxes by a utility by Steve Anger, called RAW2POV. RAW2POV can also do Phong interpolation on the triangles if desired. Any serious raytracing of large triangle databases in POV 1.0 is done with data that has been processed by RAW2POV. (Nobody tries it twice without it!) (Dan Farmer CIS[70703,1632])


POV on Mac utilities:

Thanks to "The Evil Tofu", I was recently made aware of a collection of utilites for POV which have been ported to the Mac by Eduard [esp] Shwan, of the Compuserve Group, called POV Mac Utilities 1.1. With kind permission of the author, it has been uploaded to the Internet.

The application contains the following utilities:
Coil Generator - Bill Kirby
Connect the Dots (CDTS) - Truman Brown
Dat2POV - Drew Wells
DXF2POV - Aaron A. Collins
"Lissa" Lissajous Generator - Eduard [esp] Schwan
POV Suds Generator - Sam Hobbs & Dan Farmer
Raw2POV - Steve Anger
Shell Generator - Dan Farmer
Sponge Generator - Stephen Coy
Swoop - Douglas Otwell

Also I think worthy of mention is that Paul D. Bourke's Vision-3D modeller for the Mac, which can export DXF files, supports lathing and extruding capabilities. Hmm, I wonder if I lathed something and used Mac POV Utils to generate a DXF -> POV? Paul has also recently written a program, BitSurface, which will generate DXF from bitmap files. Hmm, again....

Mac POV Utils 1.1 can be found at summex-aim.stanford.edu, /info-mac/grf/util/pov-utilities-11.hqx Freeware.

Vision-3D and BitSurface can be found at wuarchive.wustl.edu, /mirrors/architec Shareware.

(Helmut Dotzlaw, dotzlaw@CCU.UMANITOBA.CA)


> Does anyone have a leaf generator ? a tree generator ? flowers ?
Look at treebas (tree generator in qbasic (msdos))

> Is there a technique for getting that rainbow effect that you see on a
> Compact Disc ?
Look at the texture in bubble.pov (an iridescent, shimmering rainbow smear).

Both are available by anonymous ftp in ftp.informatik.uni-oldenburg.de:pub/dkbtrace/incoming mirrored on wuarchive.wustl.edu:graphics/graphics/mirrors/ftp.infor... (Tony Audas, taudas@UMCC.UMICH.EDU)


Xmgf 1.1 Motif based 3D Object Viewer

xmgf can be found on
	export.lcs.mit.edu in /contrib
You'll need MOTIF and patience (:-))
Have fun and feedback will be welcomed (good and bad!:-(
(Paul Hoad, P.Hoad@ee.surrey.ac.uk)


SIGGRAPH May issue on-line

By popular demand, we have created a tar'ed and compress'ed version of the May '93 experimental online edition of the SIGGRAPH "Computer Graphics" newsletter. It is in file


available via anonymous ftp from siggraph.org. This file contains the PostScript version of the newsletter. It is 3.2MB in size compressed and uncompresses to 15MB. (Sue Mair, mair@ucs.ubc.ca)


A friend of mine Jason Wilson created a very basic radiosity package. This package runs on the Next Platform(version 3.0 or higher).


(Leslie Donaldson, Donaldlf@cs.rose-hulman.edu)


MacCubeView 1.0.0

A 3D image display programme for the Macintosh is now available via anonymous ftp from ftp://ftp.hawaii.edu/mirrors/info-mac/sci/mac-cube-view-16.hqx. This programme is suitable for viewing 3D eight bit medical images. A 3D MR image of the author's head is included. (Daniel W. Rickey, physics@escape.ca)


Some weeks ago we sent a public message with the press-release of Real-Light 1.0, a radiosity based rendering package. People interested in watching some RGB image of environments created by Real-Light can take them by anonymous ftp at:

	ftp.iunet.it (

in the directory:


(Cristiano Palazzini, atma@relay1.iunet.it)


There is an interesting 3D Space Shuttle model database in .dxf (AutoCad), .nff (neutral file format for Sense8) and .vid (amiga VideoScape)

ftp anonymous:  artemis.arc.nasa.gov  (
in /sig-wtk/models directory
(Emerico Natonek, natonek@imtsg5.epfl.ch)


|> Is there any public domain code out there for generating polygonal models |> of human faces given a small set of parameters?

There are some things available by anonymous ftp to wuarchive.wustl.edu, under graphics/graphics/misc/facial-animation. (James R. (Jim Bob) Bill, jimbob@rainier.ucsc.edu)


Thanx to Juhana the PostScript version of my thesis can be obtained from: nic.funet.fi:pub/sci/papers/graphics/suma93.tar.gz (1115072 bytes)

He promises that it will be made available from:

The file is GNU zip compressed. (He says GNU zip gives him better compression.) So `gunzip' has to be used for uncompression. (Sumanta N. Pattanaik, sumant@saathi.ncst.ernet.in)

%A Sumanta N. Pattanaik
%T Computational Methods for Global Illumination and Visualisation of Complex
3D Environments
%R PhD thesis
%I Birla Institute of Technology & Science, Computer Science Department,
Pilani, India
%D November 1990
%K adjoint illumination equations, particle model of light, random walk,
importance sampling


Given the number of modelers coming out for ray tracers (IRIT 4.0 should be out soon, by the way), I thought I should give a plug to Ken Shoemake's wonderful ArcBall technique for interactive rotations of objects. The original paper is:

AUTHOR       = "Ken Shoemake",
TITLE        = "ARCBALL: A User Interface for Specifying Three-Dimensional
Orientation Using a Mouse",
PROCEEDINGS  = Graphics Interface '92,
YEAR         = 1992,
PAGES        = pp151

It's a very intuitive, easy to implement technique which can be used for unconstrained or constrained rotations. I needed one hint to understand the full functionality of the technique; other than that, it was obvious to use. The short paper (available on the net for the Mac, see below) explains it all. (Eric Haines)


An example written for the Mac by Shoemake is available on linc.cis.upenn.edu in the directory /pub/graphics/arcball. The file arcball is the example, while the arcball-paper is the GI paper.

Note: to decode the files, you need to use BinHex 4.0. BinHex 5.0 will not work for these files, unless you are willing to edit off the heading portion of them. (Duanfeng He (Jackson), Duanfeng.He@AtlantaGa.NCR.com)


I have a version of Shoemake's ArcBall I wrote and I'm making it available. You'll have to do some work, however, as it uses my graphics library. You have to know enough about programming in your own 3d library to be able to convert some types and routines, although it will be _really_ simple ... a matter of finding equivalents for types such as vectors and matrices, and using your own draw routines. If you use something like GL, it will be trivial, as that's what my graphics library is based on.

It's available on

That said, I'd like to thank Ken for his excellent paper. The ARCBALL concept aside, the arc drawing routines are pretty darn cool. :-)

(Blair MacIntyre, bm@shadow.columbia.edu)


Hidden surface renderer (well, it's not really ray tracing related, but I'm not a purist):

>I'm after a Gourand Z-buffer polygon scanline example. The one in
>Gems I (PolyScan) looks pretty good but as poly_scan.c is dated
>1985 and 1989, I was wondering if any improvements or optimizations
>have been made (or bug fixes). I haven't used the code as it is
>but am looking around before writing my own redering library.

You may want to grab libXG-2.0.tar.Z from ftp.ai.mit.edu down (pub/users/sundar). It has examples of sutherland-hodgman clipping, z-buffer scanline code etc. The doc directory contains a postscript manual which documents all the functions. (This is a 3-d graphics library that runs under X).

It doesn't aim to be super-fast, but it does handle multiple-polygons with loops (or holes), inter-penetrating polygons, polygons with cyclical overlap etc. (Sundar Narasimhan, sundar@ai.mit.edu)


Least impressive ray tracer dept:

A recent issue of RS/Magazine has an article on using the IBM RS/6000 for mechanical CAD and they found it worthwhile to include a picture of an RX/6000 displaying a ray traced picture of a first level sphereflake. They liked it so much they used it three times! But, since it's only first level (a big sphere surrounded by several spheres just a bit smaller) it doesn't exactly cry out that the RS/6000 is a power cruncher, does it. (Tim O'Connor)

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Simple Sphere Tessellation, by Mike Castle (mcastle@cs.umr.edu)

How sphere.c works (at wustl and other places):

Start off with 6 points on a unit sphere (1,0,0), (-1,0,0), (0,1,0), (0,-1,0), (0,0,1), (0,0,-1). These form a octahedron. Each of the 8 triangles is taken one at a time. Take one triangle, and choose its midpoint (by averaging the coordinates of the three points). Normalize that point, so it's now projected back onto the unit sphere. Replace the original triangle with 3 triangles, based on the original 3 points, and the new 4th point. Recurse. (the level of recursion is user specified).

Voila, tessellated sphere.

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Syndesis CD-ROM Review, by Eric Haines

This is the CD-ROM mentioned last issue. It contains more than 600 models and more than 400 textures, and costs $200. I received a review copy during SIGGRAPH, and it's an interesting collection. The collection was made as a way of publicizing Syndesis' InterChange Plus software, which converts 3D model data in various formats.

Though it's ISO-9660 and all that, I still had problems reading it on the Gateway CDROM drive next to me. I don't know where the problem lay, but our systems administrator said such problems are fairly common. I was able to read the CDROM on other drives just fine.

There are, of course, a ton of files on the disk. There should also be more disks in the future, and Mr. Foust has a policy in which contributors whose creations are accepted get a free disk; contact him for more information. In fact, if you can identify yourself as the author of any of the works on this first disk, you can get a free disk (a bit of a "key locked in the treasure chest" situation, admittedly, since you pretty much need the disk to see if your creation is on it).

The book that comes with the disk is quite useful, as it has thumbnail grayscale images of some of the textures and some of the models included on the disk. Unfortunately, not all of them are shown; only about 160 of the 600 models are displayed, and the synthesized textures are not shown. However, the models are all listed with descriptive titles, and there is also an index which can be pretty helpful. On the disk there are summary images of the textures available, showing thumbnail sketches of all textures available.

The models come in 3D Studio, Autocad DXF, Imagine IOB, Wavefront OBJ, and Lightwave formats. (I should note that it's pretty easy to convert from IOB to many formats by using the converter at wuarchive.wustl.edu in /graphics/graphics/objects/TDDD). The models vary in quality, of course, but the disk is not a collection of every free model ever made; while limited to what was out there for free, there are few trivial or poorly modeled objects. The scope is quite amazing, and Syndesis has done quite a job in making this collection.

On the disk there are some interesting models from Viewpoint which were supposed to be in their SIGGRAPH '93 free distribution, but in fact were not distributed there (they distributed a bunch of beach related models instead): a car, Big Ben, a deer head, elbow bones, and various military hardware.

The textures are all tileable and in TIFF/GIF/IFF formats. It's a little annoying that the tiff images do not have the standard "*.tif" suffix. The textures overall are usable, but nothing fantastic. The synthetic textures (some 262 of these) are 256x256 and some are pretty interesting, but they tend to have the same feel to them. The other textures (about 150 of these, described below) are fairly low resolution, 128x128 at very best. Some of these are tileable simply by doing mirroring along the x and y axes. All in all, some cute stuff, but don't expect a professional quality tileable wood or marble here.

In addition, in a demos directory there are a bunch of stills and FLI animations for the various companies whose work is on the disk. There is also a text area with an archive of the Imagine and Lightwave electronic mailing lists - literally megabytes of advice here.

All in all, this is a great resource for amateurs and professionals who make 3D images. Some of the models are incredible, and the textures, while not particularly fantastic in and of themselves, I consider pure icing. There's a lot to explore here. Considering that a single model from Viewpoint can cost much more than this entire disk, if you're a professional and use even just a few models from this CDROM you're ahead of the game.


John Foust notes:

About 135 of the textures were captured and massaged from hand-made, public domain Macintosh desktop textures - PPAT resources, they call them. The others were generated by a super Mac program called Texture Synth, which uses a few basic seed textures, recombined with color and multiple sine-wave textures. They look very nice, a little synthetic at times, but in an organic-synthetic sort of way...

Contact: John Foust / Syndesis Corporation (76004.1763@CompuServe.COM)

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Ray Tracing Related Abstracts from the Proceedings of Graphics Interface '93 (May 19-21, 1993, Toronto, Ont. CA).

These proceedings are available from Morgan Kaufmann Publishers, 415-965-4081. ISBN 0-9695338-2-9

%A Alain Fournier
%A Pierre Poulin
%T A Ray Tracing Accelerator Based on a Hierarchy of 1D Sorted Lists

%A Jon Genetti
%A Dan Gordon
%T Ray Tracing With Adaptive Supersampling in Object Space

%A David P. Dobkin
%A Don P. Mitchell
%T Random-Edge Discrepancy of Supersampling Patterns

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Ray Tracing Papers in the First Bilkent Computer Graphics Conference, ATARV-93, Ankara, Turkey, July 1993

"A Parallel Implementation of a Ray Tracer on a Shared Memory Multiprocessor" E. Camahort, G. Quintana, R. Vivo, and A. M. Vidal, Departamento de Sistemas Informaticos y Computacion, Universidad Politecnica de Valencia, SPAIN.

"An Efficient Parallel Spatial Subdivision Algorithm for Parallel Ray Tracing Complex Scenes" V. Isler, C. Aykanat, and B. Ozguc, Dept. of Computer Eng. and Information Science, Bilkent University, TURKEY.

"Modelling Rodin's Thinker: A Case Study Combining PHIGS and Ray-tracing" G. Williams, A. Murta, and T. Howard, Dept. of Computer Science, University of Manchester, U.K.

"A File Format for Interchange of Realistic Scene Descriptions" P. Guitton and C. Schlick, LaBRI, Talence, FRANCE.

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Fourth Eurographics Workshop on Rendering, Paris, France June 14-16, by Francois Sillion (sillion@dmi.ens.fr)

[There may be some proceedings left for sale, contact Francois for information]

The program included 24 contributed papers on a variety of topics and three invited presentations.

	Dynamic Stratification
		Andrew Glassner
	Progressive Ray Refinement for Monte Carlo Radiosity
		Martin Feda, Werner Purgathofer
	Invited: Realism in real-time ?
		Erik Jansen
	Making Shaders More Physically Plausible
		Robert Lewis
	Illumination of Dense Foliage Models
		Christopher Patmore
	A Customizable Reflectance Model for Everyday Rendering
		Christophe Schlick
	Importance and Discrete Three Point Transport
		Larry Aupperle, Pat Hanrahan
	A Continuous Adjoint Formulation for Radiance Transport
		Per Christensen, David Salesin, Tony DeRose
	Wavelet Projections for Radiosity
		Peter Schroeder, Steven Gortler, Michael Cohen, Pat Hanrahan
	Continuous Algorithms for Visibility: The Space Searching Approach
		Jenny Zhao, David Dobkin
	Invited paper : Viewpoint Analysis of Drawings and Paintings
	Rendered Using Multiple Viewpoints: Cases Containing Rectangular Objects
		Yoshihisa Shinagawa, Saeko Miyoshi, Tosiyasu Kunii
	Constant-Time Filtering by Singular Value Decomposition
		Craig Gotsman
	Measuring the Quality of Antialiased Line Drawing Algorithms
		Terence Lindgren, John Weber
	Invited: "How to solve it ?"
		Pat Hanrahan
	Numerical Integration for Radiosity in the presence of Singularities
		Peter Schroeder
	Optimal Hemicube Sampling
		Nelson Max, Roy Troutman
	Fast Calculation of Accurate Form Factors
		Georg Pietrek
	Grouping of Patches in Progressive Radiosity
		Arjan Kok
	Blockwise Refinement -- A New Method for Solving the Radiosity Problem
		Gunther Greiner, Wolfgang Heidrich, Philipp Slusallek
	Analysis and Acceleration of Progressive Refinement Radiosity Method
		Min-Zhi Shao, Norman Badler
	Texture Mapping as a fundamental Drawing Primitive
		Paul Haeberli, Mark Segal
	A Methodology for Description of Texturing Methods
		Pascal Guitton, Christophe Schlick
	Visualization of Mixed Scenes based on Volumes and Surfaces
		Dani Tost, Anna Puig, Isabel Navazo
	Physically Realistic Volume Visualization for Interactive Image Analysis
		H.T.M. Van der Voort, H.J. Noordmans, J.M. Messerli,
		A.W.M. Smeulders
	Reconstruction of Illumination functions using Bicubic Hermite
		Rui Manuel Bastos, Antonio Augusto de Sousa,
		Fernando Nunes Ferreira
	Mesh Redistribution in Radiosity
		Miguel P.N. Aguas, Stefan Muller
	Accurate Rendering of Curved Shadows and Interreflections
		G.R. Jones, C.G. Christou, B.G. Cumming, A.J. Parker

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Gamma Correction Frequently Asked Questions, by Graeme Gill (graeme@labtam.labtam.oz.au)

I get regular questions about gamma correction since I go to great pains to deal with it properly in xli (the image loader program I maintain).

Here is an explanation I often use to answer these questions.


"A note on gamma correction and images"

Author: Graeme W. Gill

Date: 93/5/16

"What is all this gamma stuff anyway?"

Although it would be nice to think that "an image is an image", there are a lot of complications. Not only are there a whole bunch of different image formats (gif, jpeg, tiff etc etc), there is a whole lot of other technical stuff that makes dealing with images a bit complicated. Gamma is one of those things. If you've ever downloaded images from BBS or the net, you've probably noticed (with most image viewing programs) that some images look ok, some look too dark, and some look too light. "Why is this?" you may ask. This, is gamma correction (or the lack of it).

Why do we need gamma correction at all?

Gamma correction is needed because of the nature of CRTs (cathode ray tubes - the monitors usually used for viewing images). If you have some sort of real live scene and turn it into a computer image by measuring the amount of light coming from each point of the scene, then you have created a "linear" or un-gamma-corrected image. This is a good thing in many ways because you can manipulate the image as if the values in the image file were light (i.e. adding and multiplying will work just like real light in the real world). Now if you take the image file and turn each pixel value into a voltage and feed it into a CRT, you find that the CRT _doesn't_ give you an amount of light proportional to the voltage. The amount of light coming from the phosphor in the screen depends on the the voltage something like this:

Light_out = voltage ^ crt_gamma

So if you just dump your nice linear image out to a CRT, the image will look much too dark. To fix this up you have to "gamma correct" the image first. You need to do the opposite of what the CRT will do to the image, so that things cancel out, and you get what you want. So you have to do this to your image:

gamma_corrected_image = image ^ (1/crt_gamma)

For most CRTs, the crt_gamma is somewhere between 1.0 and 3.0.

The problem is that not all display programs do gamma correction. Also not all sources of images give you linear images (Video cameras or video signals in general). Because of this, a lot of images already have some gamma correction done to them, and you are rarely sure how much. If you try and display one of those images with a program that does gamma correction for you, the image gets corrected twice and looks way to light. If you display one of those images with a program that doesn't do gamma correction, then it will look vaguely right, but not perfect, because the gamma correction is not exactly right for you particular CRT.

Whose fault is all this?

It is really three things. One is all those display programs out there that don't do gamma correction properly. Another is that most image formats don't specify a standard gamma, or don't have some way or recording what their gamma correction is. The third thing is that not many people understand what gamma correction is all about, and create a lot of images with varying gamma's.

At least two file formats do the right thing. The Utah Graphics Toolkit .rle format has a semi-standard way of recording the gamma of an image. The JFIF file standard (that uses JPEG compression) specifies that the image to be encoded must have a gamma of 1.0 (i.e. a linear image - but not everyone obeys the rules).

Some image loaders (for instance xli - an X11 image utility) allow you to specify not only the gamma of the monitor you are using, but the individual gamma values of image you are trying to view. Other image viewers (e.g. xv, another X11 image program) and utilities (e.g. the pbm toolkit) provide ways of changing the gamma of an image, but you have to figure out the overall gamma correction yourself, allowing for undoing any gamma correction the image has, and then the gamma correction you need to suite your CRT monitor.

[Note that xv 2.21 doesn't provide an easy way of modifying the gamma of an image. You need to adjust the R, G and B curves to the appropriate gamma in the ColEdit controls. Altering the Intensity in the HSV controls doesn't do the right thing, as it fails to take account of the effect gamma has on H and S. This tends to give a tint to the image.]

The simplest way to do that is to try loading the file chkgamma.jpg (provided with xli distribution), which is a JFIF jpeg format file containing two grayscale ramps. The ramps are chosen to look linear to the human eye, one using continuous tones, and the other using dithering. If your viewer does the right thing and gamma corrects images, then the two ramps should look symmetrical, and the point at which they look equally bright should be almost exactly half way from the top to the bottom. (To find this point it helps if you move away a little from the screen, and de-focus your eyes a bit.)

If your viewer doesn't do gamma correction, then left hand ramp will have a long dark part and a short white part, and the point of equal brightness will be above the center.

If your viewer does have a way of setting the right amount of gamma correction for a display, then if the equal brightness point is above center increase the gamma, and decrease it if it is below the center. The value will usually be around 2.2.

[with xli for instance, you can adjust the display gamma with the -dispgamma flag, and once you've got it right, you can set the DISPLAY_GAMMA environment variable in your .profile]

This is the most tricky bit. As a general rule it seems that a lot of true color (i.e. 24 bit, .ppm .jpg) images have a gamma of 1.0 (linear), although there are many about that have some gamma correction. It seems that the majority of pseudo color images (i.e. 8 bit images with color maps - .gif etc.) are gamma corrected to some degree or other.

If your viewer does gamma correction then linear images will look good, and gamma corrected images will look too light.

If your viewer doesn't do gamma correction, then linear images will look too dark, and gamma corrected images will ok.

One of the reason that many high quality formats (such as Video) use gamma correction is that it actually makes better use of the storage medium. This is because the human eye has a logarithmic response to light, and gamma correction has a similar compression characteristic. This means images could make better use of 8 bits per color (for instance), if they used gamma correction. The implication, though, is that every time you want to do any image processing you should convert the 8 bit image to 12 or so linear bits to retain the same accuracy. Since little popular software does this, and none of the popular image formats can agree on a standard gamma correction factor, it is difficult to justify gamma corrected images at the popular level.

If some image formats can standardize on a particular gamma, and if image manipulation software takes care to use extra precision when dealing with linearized internal data, then gamma corrected distribution of images would be a good thing.

(I am told that the Kodak PhotoCD format for instance, has a standard gamma correction factor that enables it to get the highest quality out of the bits used to hold the image).

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3D Studio Rendering, by Chris Williams (chrisw@fciad2.bsd.uchicago.edu)

> I've read numerous times in this newsgroup that Autodesk 3d Studio v2
>doesn't support ray-tracing. I'm just wondering how one renders images
>with lights/objects casting shadows as well as reflection mapping materials
>without raytracing. Can someone tell me what I'm missing here?

Shadows are done via Z-buffering. Imagine that you wish to have an object cast a shadow on a floor. Render the scene once from the point of view of the shadow-casting spotlight. The areas that are obscured in that image (the underside of the object and part of the floor) will be in shadow when rendered from the regular camera. When the scene is actually rendered that image (which also contains depth information i.e. how far each surface was from the shadow-spot) is used to to determine what is and isn't in shadow.

Reflections are done with reflection maps or cubic environment maps. Take the example of a chrome ball on a checkered floor (please). Place the camera *inside* the chrome ball. Render six images, one in each of the cardinal directions, square. These six (pos X, neg X, pos Y, neg Y, pos Z and neg Z) are combined into one image that is "wrapped around" the ball. It usually works pretty well. Frankly, most people pay little attention to the content of a reflection, and it's possible to cheat like a professional wrestling villian. One other advantage of reflection maps, once the reflected items are in the map, if they aren't otherwise visible in the scene, they no longer need to be in the scene. In raytracing, every reflected object has to be there, and costs quite a bit. If your object is a brushed metal, for instance, you can just paint blobs of color and blur the whole thing and use *that* as your reflection map.

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Ray-Bezier Patch Intersection, by Chuck McKinley, Max Froumentin (mckinley@fed3005.ne1300.ingr.com, froument@lifl.lifl.fr)

Chuck McKinley writes:

If some kind person has access to a mathematical package such as Mathematica, Maple,... I would like to ask you for the solution to the following problem. I sometimes have algebra problems like this where I would like a simplified symbolic solution. Is there a FTP-able package out there that can handle such beasts?

I would like to solve the following ray - Bezier patch intersection for the scalar constant t in:

P                    + t * V                =  Q(u,w)
 (origin point in 3D)       (dir vector 3D)


Max Froumentin replies:

Well, there is a formula. But you probably don't want to know it: One usual method is to write the Bezier parametric equation (Q(u,v)=...) in the form of an implicit surface (f(x,y,z)=0 where f is a polynomial). You can then insert the parametric equations of your ray and get a equation in t, giving you the intersection points. That's all right for low degree surfaces like planes or quadrics. But for a Bezier patch of parametric degree n, the resulting implicit equation is of degree 2n^2. As you use degree 3 Bezier patches, you will get an implicit equation of degree 18! Even if you type the whole formula in your program, you probably know of the extremely low accuracy of high-degree polynomials in computers...

Instead, people use approximation methods, like two-dimensional Newton iteration. See the book by Glassner on ray-tracing for further details, or look at the POV source code.

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Turbulence and Noise, by Ken Perlin

[Since course notes are so hard to get, I thought I would reprint this. Bernie Kirby sent this to Thomas Setzer, who posted it, and now it's here.]


			       Ken Perlin
			   New York University


3.6.1 The turbulence function

The turbulence function, which you use to make marble, clouds, explosions, etc., is just a simple fractal generating loop built on top of the noise function. It is not a real turbulence model at all. The key trick is the use of the fabs() function, which makes the function have gradient discontinuity "fault lines" at all scales. This fools the eye into thinking it is seeing the results of turbulent flow. The turbulence() function gives the best results when used as a phase shift, as in the familiar marble trick:

    sin(point + turbulence(point) * point.x);

Note the second argument below, lofreq, which sets the lowest desired frequency component of the turbulence. The third, hifreq, argument is used by the function to ensure that the turbulence effect reaches down to the single pixel level, but no further. I usually set this argument equal to the image resolution.

float turbulence(point, lofreq, hifreq)
float point[3], freq, resolution;
	float noise3(), freq, t, p[3];

	p[0] = point[0] + 123.456;
	p[1] = point[1];
	p[2] = point[2];

	t = 0;
	for (freq = lofreq ; freq < hifreq ; freq *= 2.) {
		t += fabs(noise3(p)) / freq;
		p[0] *= 2.;
		p[1] *= 2.;
		p[2] *= 2.;
	return t - 0.3; /* readjust to make mean value = 0.0 */

3.6.2 The noise function

noise3 is a rough approximation to "pink" (band-limited) noise, implemented by a pseudorandom tricubic spline. Given a vector in 3-space, it returns a value between -1.0 and 1.0. There are two principal tricks to make it run fast:

- Precompute an array of pseudo-random unit length gradients g[n].

- Precompute a permutation array p[] of the first n integers.

Given the above two arrays, any integer lattice point (i,j,k) can be quickly mapped to a pseudorandom gradient vector by:

    g[ (p[ (p[i] + j) % n ] + k) % n]

By extending the g[] and p[] arrays, so that g[n+i]=g[i] and p[n+i]=p[i], the above lookup can be replaced by the (somewhat faster):

    g[ p[ p[i] + j ] + k ]

Now for any point in 3-space, we just have to do the following two steps:

(1) Get the gradient for each of its surrounding 8 integer lattice points as above.

(2) Do a tricubic hermite spline interpolation, giving each lattice point the value 0.0.

The second step above is just an evaluation of the hermite derivative basis function 3 * t * t - 2 * t * t * t in each by a dot product of the gradient at the lattice.

Here is my implementation in C of the noise function. Feel free to use it, as long as you reference where you got it. :-)

/* noise function over R3 - implemented by a pseudorandom tricubic spline */


#define DOT(a,b) (a[0] * b[0] + a[1] * b[1] + a[2] * b[2])

#define B 256

static p[B + B + 2];
static float g[B + B + 2][3];
static start = 1;

#define setup(i,b0,b1,r0,r1) \
	t = vec[i] + 10000.; \
	b0 = ((int)t) & (B-1); \
	b1 = (b0+1) & (B-1); \
	r0 = t - (int)t; \
	r1 = r0 - 1.;

float noise3(vec)
float vec[3];
	int bx0, bx1, by0, by1, bz0, bz1, b00, b10, b01, b11;
	float rx0, rx1, ry0, ry1, rz0, rz1, *q, sy, sz, a, b, c, d, t, u, v;
	register i, j;

	if (start) {
		start = 0;

	setup(0, bx0,bx1, rx0,rx1);
	setup(1, by0,by1, ry0,ry1);
	setup(2, bz0,bz1, rz0,rz1);

	i = p[ bx0 ];
	j = p[ bx1 ];

	b00 = p[ i + by0 ];
	b10 = p[ j + by0 ];
	b01 = p[ i + by1 ];
	b11 = p[ j + by1 ];

#define at(rx,ry,rz) ( rx * q[0] + ry * q[1] + rz * q[2] )

#define surve(t) ( t * t * (3. - 2. * t) )

#define lerp(t, a, b) ( a + t * (b - a) )

	sx = surve(rx0);
	sy = surve(ry0);
	sz = surve(rz0);

	q = g[ b00 + bz0 ] ; u = at(rx0,ry0,rz0);
	q = g[ b10 + bz0 ] ; v = at(rx1,ry0,rz0);
	a = lerp(sx, u, v);

	q = g[ b01 + bz0 ] ; u = at(rx0,ry1,rz0);
	q = g[ b11 + bz0 ] ; v = at(rx1,ry1,rz0);
	b = lerp(sx, u, v);

	c = lerp(sy, a, b);          /* interpolate in y at lo x */

	q = g[ b00 + bz1 ] ; u = at(rx0,ry0,rz1);
	q = g[ b10 + bz1 ] ; v = at(rx1,ry0,rz1);
	a = lerp(sx, u, v);

	q = g[ b01 + bz1 ] ; u = at(rx0,ry1,rz1);
	q = g[ b11 + bz1 ] ; v = at(rx1,ry1,rz1);
	b = lerp(sx, u, v);

	d = lerp(sy, a, b);          /* interpolate in y at hi x */

	return 1.5 * lerp(sz, c, d); /* interpolate in z */

static init()
	long random();
	int i, j, k;
	float v[3], s;

/* Create an array of random gradient vectors uniformly on the unit sphere */

	for (i = 0 ; i < B ; i++) {
		do {                            /* Choose uniformly in a cube */
			for (j=0 ; j<3 ; j++)
				v[j] = (float)((random() % (B + B)) - B) / B;
			s = DOT(v,v);
		} while (s > 1.0);              /* If not in sphere try again */
		s = sqrt(s);
		for (j = 0 ; j < 3 ; j++)       /* Else normalize */
			g[i][j] = v[j] / s;

/* Create a pseudorandom permutation of [1..B] */

	for (i = 0 ; i < B ; i++)
		p[i] = i;
	for (i = B ; i > 0 ; i -= 2) {
		k = p[i];
		p[i] = p[j = random() % B];
		p[j] = k;

/* Extend g and p arrays to allow for faster indexing */

	for (i = 0 ; i < B + 2 ; i++) {
		p[B + i] = p[i];
		for (j = 0 ; j < 3 ; j++)
			g[B + i][j] = g[i][j];

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Ray Tracing Research Ideas, by Klaus Lisberg Kristensen (lisberg@daimi.aau.dk) & Christian Gautier

[Some of these ideas have already been researched a bit, some ideas I don't understand, but I thought I'd pass on the list. -EAH]

We put a request out for research topics in ray tracing. We have received a lot of good ideas, articles etc., and we are now going through all of them.

The areas suggested are (in very short terms):

- Methods to model the colors using spectral curves for the light sources. This could help problems like color-aliasing and machine dependency.

- Modelling reflections from oil in a water puddle, turbulent water stream, human bodies(or dinosaurs :)) by modelling every muscle.

- Modelling dirt was suggested by several people.

- Alternative ray-tracing methods.

- Non-realistic rendering.

- Don Mitchell's interval arithmetic approach to intersection.

- A memory-efficient algorithm for discrete ray-tracing.

- Radiosity simulation by stochastic ray-tracing.

- Optically correct lens emulators.

- Modelling clouds, misty nights or a river in the mountains.

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POV-Ray Utilities, by Dan Farmer (70703.1632@CompuServe.COM)

(This listing is about a year out-of-date)

[I thought I would include this old list to give a sense of the support out there for POV. There's lots more out there than just this - anyone with a current list, please do send it on. -EAH]

Object Creation Utilities
CHAIN101.ZIP = Chain generator.
CHEMCONV.ZIP = Convert data from Larry Puhl's CHEM molecular modeller.
CM.ZIP       = CircleMaster - Truman Brown - allows you to create clipped
	       spheres and ellipses that can cap your hyperboloids of two
	       sheets perfectly giving the illusion of quartic blobs.
WORM02.ZIP   = Paint with spheres to generate points for CTDS.
CTDS.ZIP     = Connect The Dots Smoother - Truman Brown.  Raytrace sources.
	       makes your WORM output POV compatible.  Writes a file using
	       the WORM data, with your choice of spheres or ellipsoids, and
	       will either connect the spheres with cones and cylinders, or
	       just output the "dots."
FONT2DAT.ZIP = Converts GRASP .fnt and .set font files to POV-Ray text.
	       Fonts included.
FRGEN13.ZIP  = Midsection triangular displacement fractal surface generator.
LISS152.ZIP  = Generate 3D Lissajous traces with spheres.
LISSAJ.ZIP   = Another Lissajous path generator, w/graphics preview.
PICKSHEL.ZIP = Make snail shells from spheres.
POVCOIL2.ZIP = Hard to describe twisted coil objects.  POV Sources
POVTORUS.ZIP = Makes torus-like objects using cylindrical sections. SHADE1.ZIP
  = "Lampshade" generator.
SPIKE.ZIP    = Generate shapes with radial projection.
SPRING12.ZIP = Generates and animates springs.
SUDS.ZIP     = Generates a "glob" of tangent spheres, rather like suds.
TTG.ZIP      = Creates POV-Ray torus data, the easy way - Truman Brown
TWISTER.ZIP  = Twisted objects such as Archimedes spirals.
SWOOP.ZIP    = Hard to describe extrusion generator.  Very versatile.

Miscellaneous Utilities
	       allows you to drop in and design that elusive color/lighting
	       combination that you are looking for - it shines when it
	       comes to designing just the right surface qualities.  Lets
	       you interactively play with many texture variables and see
	       them rendered almost instantly on screen, then dump the
	       texture to a POV file.  Highly recommended for learning about
	       textures.  POV sources.
MAKETILE.ZIP = Actually a PICLAB script.  Great for making imagemaps.
SPLITPOV.ZIP = Run a POV-Ray image in sections on multiple computers
	       and glue them back together automatically.  Best
	       for use over a network.  Generates batchfiles.
TCE201  .ZIP = The Color Editor - Dan Farmer.  A color viewer/editor.
	       Create/edit your colors.inc file.

Animation Utilities
ACCEL.ZIP    = Generate acceleration data for use in an animation.

ANIMK05B.ZIP = Excellent animation generator.

CAMPATH1.ZIP = Generate circular, lemniscate, polar, and other camera path

RTAG.ZIP     = Special animation language (shareware)

ANIBATCH.ZIP = Simple linear motion, generates a single batch file that
	       creates frame data at runtime.

AWKBLOB.AWK  = Converts raw sphere data in the form of x y z r into blob
	       components for POV-Ray.

HSM2POV.AWK  = Convert data from Mira Imaging's "Hyperspace" format to
	       POV-Ray triangle data.

HSM2RAW.AWK  = Convert data from Mira Imaging's "Hyperspace" format to raw
	       triangle data. By adding a sphere radius to the output vector
	       and running the output through AWKBLOB.AWK, you could also
	       convert "Hyperspace" data to blobs.

Data Conversion Utilities
RAW2POV.ZIP  = Steve Anger - raw triangle vector data to well-bounded
    POV-Ray format as either normal, or Phong-shaded triangles.  Very useful
    with other programs, but it doesn't really do anything by itself.
3DS2POV.ZIP  = AutoDesk 3D-Studio ASCII data to POV-Ray files.
3D2POV15.ZIP = Amiga Sculpt3D to POV-Ray format.
3D2-POV      = Cyber Sculpt (Atari) 3D2 files.
DXF2POV.ZIP  = AutoCAD and other DXF file data to POV-Ray files.
SA2POV.ZIP   = Sculpt-Animate data to POV-Ray files.
SNDPPR.ZIP   = raw triangle data to Phong-shaded.
VCAD2POV.ZIP = Versa-CAD to POV-Ray.

As I mentioned above, this listing is old, and is very definitely only a sampler of what is available. Almost all of these are free, the rest are inexpensive shareware. Most are available on CIS (GO GRAPHDEV), YCCMR BBS (Chicago. (708) 358-5611, or TGA BBS (510) 524-2780 as well as many of the nodes of the PCGNet, of which TGA is a hub.

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SPD Platform/Compiler Results, by David Hook (dgh@ecr.mu.oz.au)

[many thanks to David and Bernie Kirby for running the SPD test on a variety of platforms with various compiler options. Most of you will be bored to tears by this stuff, but I include it mostly so it gets archived somewhere. The things that are most noticeable are how performance varies between machines. Also, Rayshade does everything in doubles and most of the other ray tracers do everything in floats, so machines that can't or don't override the double<->float conversions that C requires tend to take a hit on these others. -EAH]

About the benchmarks run:
	a) The Standard Benchmarks are run using the best available
	   NFF to  converter available. For example, this
	   means that the awk script for rayshade was used as it
	   supplied a default grid of 22x22x22, where as the "other"
	   converter didn't. The rational behind this is that if the
	   rayshade people have it in their converter, then it is the
	   preferred option.

	b) The "tweaked" benchmarks are run with various grids and with
	   the ground or backing polygon removed thus:

	   balls:  20x20x20        - take background out of grid structure.
	   gears:  21x21x21        - take background out of grid structure.
	   mount:  21x21x21
	   rings:  21x21x21        - take background out of grid structure.
	   teapot: 22x22x22        - The floor IS kept!
	   tetra:  16x16x16
	   tree:   21x21x21        - take background out of grid structure.

	   These pertain only to the ART/rayshade results, where the tweaking
	   could be easily done. I hate to be the one to say this, but, it
	   looks as if in some cases this actually slows the renderer down.

	   These results are presented in a separate table as it didn't
	   seem realistic (or fair) to compare the different ray tracers
	   by massaging the input files. In any case they are only relevant
	   to balls, gears, rings, and tree. The figures for art using a
	   kdtree, where provided, indicate that taking the backing polygon
	   out results in a nicely distributed data set in the subdivision
	   and using a non-uniform subdivision is more a hindrance than a
	   help (which is basically what you'd expect...).

	   [There are art/kd results, where art uses a KD-tree for efficiency,
	   and art/ug results, where art uses a uniform grid.  Both versions of
	   the code are available on the net. -EAH]

	c) All programs are compiled with Maximum optimization/and appropriate
	   floating point. In the case of Art/Vort/*/dp this means that the
	   -float, -fsingle or whatever was not used but that everything was
	   compiled with -Dfloat=double.

	d) The Bob/Vivid raytracer had its "robust" memory allocation
	   scheme replaced with "standard" malloc's as the robust scheme caused
	   core dumps on SGI and RS6000 machines.

	e) All Benchmarks include the time taken to read the scene in.

	f) All times are in CPU seconds.

	g) We don't own any SGI, RS6000 or HP machines. The use of these
	   machines was kindly allowed by their respective owners/admins.
	   As such, we couldn't run every raytracer as we were wearing
	   out our welcome as it was.

	h) All runs were done to completion at 512x512 pixels.

	i) We DID try to run POV, but as it was taking over 24 hours of CPU
	   time we simply had to stop.  Perhaps there is an NFF converter
	   that inserts some bounding boxes automatically?

	j) Ratios calculated below for the Standard SPDs are done on the
	   basis of Art/Vort/kd == the base line (it's the first in alphabetical

	k) In all cases we used the latest available versions of the software
	   (hence the difference in Rtrace).

[I have added "*" after the fastest ratio for easy visual comparison. -EAH]

				Standard SPDs
Machine: SGI PI.
			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd		761.7	2296	414.6	1042	393.6	118.3	640.5
Art/Vort/ug		5958	1093	312.4	620.1	235.2	68	5761
Rayshade		2847	1950	899.5	1228	464	116	5602
Bob/Vivid		811	1369	446	1854	495	93.5	511
Rtrace8			1779	6236	2957	4840	1199	291	933

Art/Vort/kd		1.0 *	1.0	1.0	1.0	1.0	1.0	1.0
Art/Vort/ug		7.8	0.47 *	0.75 *	0.6 *	0.6 *	0.57 *	8.99
Rayshade		3.7	0.85	2.17	1.18	1.18	0.98	8.75
Bob/Vivid		1.06	0.6 	1.08	1.78	1.26	0.79	0.79 *
Rtrace8			2.33	2.71	7.13	4.64	3.05	2.45	1.46

Machine: IBM RS6000
			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd		591.7	1847	325	812	334	107	534
Art/Vort/ug		3537	815	234	454	187	55	3215
Rayshade		1410	846	406	548	230	70	2418
Bob/Vivid		506	909	309	1095	323	68	348
Rtrace8			861	4684	1414	2267	587	145	469

Art/Vort/kd		1.0	1.0	1.0	1.0	1.0	1.0	1.0
Art/Vort/ug		5.98	0.44 *	0.72 *	0.56 *	0.56 *	0.51 *	6.02
Rayshade		2.38	0.46	1.25	0.67	0.68	0.65	4.53
Bob/Vivid		0.86 *	0.49	0.95	1.35	0.97	0.64	0.65 *
Rtrace8			1.45	2.54	4.35	2.79	1.76	1.35	0.88

Machine: SUN SPARCstation2
			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd		705	1900	389	951	369	112	574
Art/Vort/ug		5768	974	319	570	231	71	5327
Rayshade		2422	1309	671	940	366	106	4473
Bob/Vivid		715	1181	392	1419	412	87	429.6
Rtrace8			1084	3151	1991	2950	765	204	573

			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd		1.0 *	1.0	1.0	1.0	1.0	1.0	1.0
Art/Vort/ug		8.18	0.51 *	0.82 *	0.6 *	0.62 *	0.63 *	9.28
Rayshade		3.43	0.69	1.72	0.99	0.99	0.95	7.8
Bob/Vivid		1.01	0.62	1.01	1.49	1.11	0.78	0.75 *
Rtrace8			1.54	1.66	5.12	3.10	2.07	1.82	0.99

Machine: HP 720
			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd		308	915	156	400	155	58.1	252
Rayshade		870	507	203	292	122	41.7	2079

			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd		1.0 *	1.0	1.0 *	1.0	1.0	1.0	1.0 *
Rayshade		2.82	0.55 *	1.3	0.73 *	0.78 *	0.72 *	8.25

				Tweaked SPDs

In cases where xxx appears, for one reason or another, we were unable to
run the benchmark.

Machine: SGI PI.
			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/ug/twk		208.4	1259	312.3	478.3	334.1	67.9	97.8
Rayshade/twk		377.7	2647	937	877	548	141	171

Art/Vort/ug/twk		1.0 *  	1.0 *	1.0 *	1.0 *  	1.0 * 	1.0 *	1.0 *
Rayshade/twk		1.8	2.1 	3.00	1.83	1.64	2.07	1.75

Machine: IBM RS6000
			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd/twk		353	1970.5	333.7	739.6	423.7	56.5	111.1
Art/Vort/ug/twk		153.4	887	238	352	269	56	75
Rayshade/twk		183	1078	407	428	292	88	88

Art/Vort/kd/twk		1.0  	1.0	1.0	1.0	1.0	1.0	1.0
Art/Vort/ug/twk		0.43 *	0.45 *	0.71 *	0.48 *	0.63 *	1.0 *	0.67 *
Rayshade/twk		0.52	0.55	1.22	0.58	0.68	1.56	0.79

Machine: SUN SPARCstation2
			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd/twk		417	2130	389	846	369	112	128
Art/Vort/ug/twk		202	1081	319	436	366	72	103
Rayshade/twk		293	1635	675	750	467	130	148

			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd/twk		1.0	1.0	1.0	1.0	1.0	1.0	1.00
Art/Vort/ug/twk		0.48 *	0.51 *	0.89 *	0.51 *	0.99 *	0.64 *	0.80 *
Rayshade/twk		0.70	0.77	1.74	0.89	1.27	1.16	1.16

Machine: HP 720
			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd/twk		186	1029	156	xxx	155	58.1	91
Art/Vort/ug/twk		89	527     xxx	168	138.7	41.4	39.7
Rayshade/twk		99	676	202	237	161	51.4	51.2

			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd/twk		1.0	1.0	1.0	xxx	1.0	1.0	1.0
Art/Vort/ug/twk		0.48 *	0.51 *	xxx	1.0 *	0.89 * 	0.70 *	0.42 *
Rayshade/twk		0.53	0.65	1.29 	1.41	0.96	0.88	0.56

[My figures do not seem to match these that well:  in my tests on the HP 720
Rayshade seemed to always outperform art.  We're not sure why there's a
mismatch. -EAH]

			*  *  *  *  *  *  *  *  *

			A comparison of float vs. doubles
		where float promotion to double can be disabled.

		As art seems to be the only one that declares most
		things as floats, this is the subject of these runs.

Machine: SGI PI.
	Option: Single precision -float
		Double precision -Dfloat=double

			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd		761.7	2296	414.6	1042	393.6	118.3	640.5
Art/Vort/kd/dp		978	3000	xxxx	1365	520	152	777

Art/Vort/ug/twk		208.4	1259	312.3	478.3	334.1	67.9	97.8
Art/Vort/ug/twk/dp	295	1882	449	681	514	109	141

Art/Vort/kd		1.0	1.0	1.0	1.0	1.0	1.0	1.0
Art/Vort/kd/dp		1.28	1.3 	....	1.3	1.32	1.27	1.21

Art/Vort/ug/twk		1.0  	1.0	1.0	1.0	1.0	1.0	1.0
Art/Vort/ug/twk/dp	1.4	1.49	1.43	1.42	1.53	1.6	1.44

Machine: IBM RS6000
	No such option. The times were much the same.

Machine: SUN SPARCstation2
	Option: Single precision -fsingle
		Double precision -Dfloat=double

			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd		705	1900	389	951	369	112	574
Art/Vort/kd/dp		791	xxx	413	1034	428	127	625

Art/Vort/ug/twk		202	1081	319	436	366	72	103
Art/Vort/ug/twk/dp	214	1219	341	476	1027	78	114

			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd		1.0	1.0	1.0	1.0	1.0	1.0	1.0
Art/Vort/kd/dp		1.12	xxx	1.06	1.08	1.16	1.13	1.08

Art/Vort/ug/twk		1.0	1.11	1.0	1.0	1.58	1.01	1.0
Art/Vort/ug/twk/dp	1.06	1.13	1.07	1.09	2.8	1.08	1.1

Machine: HP 720
	Option: Single precision +f
		Double precision -Dfloat=double

			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd		308	915	156	400	155	58.1	252
Art/Vort/kd/dp		300	926	138	390	155	60.3	244

Art/Vort/ug/twk		89	527	xxx	168	139	41.4	39.7
Art/Vort/ug/twk/dp	117	560	xxx	234	168	43.1	46

			balls	gears	mount	rings	teapot	tetra	tree
Art/Vort/kd		1.0 	1.0     1.0	1.0	1.0	1.0	1.0
Art/Vort/kd/dp		0.97	1.01	0.88	0.975	1.0	1.03	0.97

Art/Vort/ug/twk		1.0	1.0	xxx	1.0	1.0	1.0	1.0
Art/Vort/ug/twk/dp	1.31	1.06	xxx	1.39	1.2	1.04	1.15

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Eric Haines / erich@acm.org