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STANDARD PROCEDURAL DATABASES, by Eric Haines, 3D/Eye, Inc. [Created while under contract to Hewlett-Packard FSD and HP Laboratories] Version 3.1, as of 11/2/92 address: 3D/Eye, Inc., 2359 N. Triphammer Rd, Ithaca, NY 14850 email: erich@eye.com, wrath.cs.cornell.edu!eye!erich This software package is not copyrighted and can be used freely. History ------- Versions 1.0 to 1.5 released February to June, 1987 for testing. Version 2.0 released July, 1987. Version 2.1 released August, 1987 - corrected info on speed of the HP 320, other minor changes to README. Version 2.2 released November, 1987 - shortened file names to <=12 characters, procedure names to <= 32 characters, and ensured that all lines are <= 80 characters (including return character). Version 2.3 released March, 1988 - corrected gears.c to avoid interpenetration, corrected and added further instructions and global statistics for ray tracing to README. Version 2.4 released May, 1988 - fixed hashing function for mountain.c. Version 2.5 released October, 1988 - added NFF documentation. Version 2.6 released August, 1989 - lib_output_cylcone fix (start_norm.w was not initialized). Version 2.7 released July, 1990 - comment correction in lib.c, NFF file clarifications. Version 3.0 released October, 1990 - added teapot.c database, mountain.c changed to mount.c, additions to def.h and lib.c, changes to README and NFF, added patchlevel.h file. Version 3.1 released November, 1992 - minor typo fixes, updated FTP list, makefile update {These files use tab characters worth 8 spaces} Introduction ------------ This software is meant to act as a set of basic test images for ray tracing algorithms. The programs generate databases of objects which are fairly familiar and "standard" to the graphics community, such as the teapot, a fractal mountain, a tree, a recursively built tetrahedral structure, etc. I originally created them for my own testing of ray tracing efficiency schemes. Since their first release other researchers have used them to test new algorithms. In this way, research on algorithmic improvements can be compared in a more standardized way. If one researcher ray-traces a car, another a tree, the question arises, "How many cars to the tree?" With these databases we may be comparing oranges and apples ("how many hypercubes to a timeshared VAX?"), but it's better than comparing oranges and orangutans. In addition, this document outlines some statistics that are more meaningful to researchers than raw timing tests. Using these statistics along with the same scenes allows us to compare results in a more meaningful way. With the development and release of the Anderson benchmarks for graphics hardware, the use of the SPD package for hardware testing is somewhat redundant. Therefore I have deleted references to testing hidden-surface algorithms in this version. However, another interesting use for the SPD has been noted: debugging. By comparing the images and the statistics with the output of your own ray tracer, you can detect program errors. For example, "mount" is useful for checking if refraction rays are generated correctly, and "balls" can check for the correctness of eye and reflection rays. The images for these databases and other information about them can be found in "A Proposal for Standard Graphics Environments," IEEE Computer Graphics and Applications, vol. 7, no. 11, November 1987, pp. 3-5. See IEEE CG&A, vol. 8, no. 1, January 1988, p. 18 for the correct image of the tree database (the only difference is that the sky is blue, not orange). The teapot database was added later, and consists of a shiny teapot on a shiny checkerboard. The SPD package is available via anonymous FTP from: freedom.graphics.cornell.edu [128.84.247.85] weedeater.math.yale.edu [130.132.23.17] cs.uoregon.edu [128.223.4.13] among others. For those without FTP access, write to the netlib automatic mailer: research!netlib and netlib@ornl.gov are the sites. Send a one line message "send index" for more information, or "send haines from graphics" for the latest version of the SPD package. File Structure -------------- Eight different procedural database generators are included. These were designed to span a fair range of primitives, modeling structures, lighting and surface parameters, background conditions, and other factors. A complexity factor is provided within each program to control the size of the database generated. This software package contains the following files: README - what you are now reading NFF - a description of the Neutral File Format used in the SPD patchlevel.h - keeps track of patch level makefile - used to make the programs (in HP-UX Unix) def.h - some useful "C" definitions lib.h - globals and library routine declarations lib.c - library of routines balls.c - fractal ball object (a.k.a. sphereflake) generator gears.c - 3D array of interlocking gears generator mount.c - fractal mountain and 4 glass ball generator rings.c - pyramid of dodecahedral rings generator teapot.c - the famous teapot on a checkerboard generator tetra.c - recursive tetrahedra generator tree.c - tree generator The compiled and linked programs will output a database in ASCII to stdout containing viewing parameters, lighting conditions, material properties, and geometric information. The data format is called the 'neutral file format' (or NFF) and is described in the `NFF' file. This format is meant to be minimal and easy to attach to a user-written filter program which will convert the output into a file format of your choosing. Either of two sets of primitives can be selected for output. If OUTPUT_FORMAT is defined as OUTPUT_CURVES, the primitives are spheres, cones, cylinders, and polygons. If OUTPUT_FORMAT is set to OUTPUT_PATCHES, the primitives are output as polygonal patches and polygons (i.e. all other primitives are polygonalized). In this case OUTPUT_RESOLUTION is used to set the amount of polygonalization of non-polygonal primitives. In general, OUTPUT_CURVES is used for ray-trace timing tests, and OUTPUT_PATCHES for polygon-based algorithm timings. Note that sphere primitives are not polygonalized using the simple longitude/latitude tessellation, but rather are chopped along the six faces of a cube projected onto the sphere. This tessellation avoids generation of the cusp points at the sphere's poles and so eliminates discontinuities due to them. The size factor is used to control the overall size of the database. Default values have been chosen such that the maximum number of primitives less than 10,000 is output. One purpose of the size factor is to avoid limiting the uses of these databases. Depending on the research being done and the computing facilities available, a larger or smaller number of primitives may be desired. The size factor can also be used to show how an algorithm's time changes as the complexity increases. To generate the databases, simply type the name of the database and direct the output as desired, e.g. "balls > balls.nff" creates the default sized database and sends the output to balls.nff. A new feature in 3.0 is that you can enter the size factor on the command line, e.g. "balls 2 > balls.nff" gives a much smaller database of 91 spheres. See the header of the database C file (e.g. "balls.c") for how the size factor affects the output. Other parameters in the code itself (for example, branching angles for "tree.c" and the fractal dimension in "mount.c") are included for your own enjoyment, and so normally should not be changed if the database is used for timing tests. Because the hashing function in the original release of "mount.c" is not very good (at low resolutions there is patterning), there is a better hashing function provided which can be turned on by defining NEW_HASH. Use the old hashing function (i.e. don't change anything) for consistency with previously published results. Since the SPD package is designed to test efficiency, the actual shading of the images is mostly irrelevant. All that matters is that reflective surfaces spawn reflection rays and transmitters spawn refraction rays. For this reason the effect of the other shading parameters is up to the implementer. Note that light intensities, ambient components, etc. are not specified. These may be set however you prefer. Feel free to change any colors you wish (especially the garish colors of `rings'). The thrust of these databases is the testing of rendering speeds, and so the actual color should not affect these calculations. An ambient component should be used for all objects, so that the time to compute it is included in the ray tracing statistics. A simple formula for a relative intensity (i.e. between 0 and 1) for each light and for the ambient component is the following: sqrt(# lights) / (# lights * 2). If you desire a model for a good scene description language, NFF is not it. Instead, you should look at Craig Kolb's ray-tracer language, which is part of his excellent RayShade ray tracer, available via anonymous FTP from weedeater.math.yale.edu [130.132.23.17]. Of the public domain ray tracers, this is the one to beat in speed. Also included in his distribution is an awk filter which converts NFF files to his language. The programs all attempt to minimize program size (for ease in distributing) and memory usage, and none allocate any dynamic memory. As such, many of the programs are relatively inefficient, regenerating various data again and again instead of saving intermediate results. This behavior was felt to be unimportant, since generating the data is a one-time affair which normally takes much less time than actually rendering the scene. Database Analysis ----------------- The databases were designed with the idea of diversity in mind. The variables considered important were the amount of background visible, the number of lights, the distribution of sizes of objects, the amount of reflection and refraction, and the depth complexity (how many objects a ray from the eye passes through). balls: This database is sometimes called "sphereflake", as it is generated like a snowflake curve. This database consists mostly of various sized spheres. It has no eye rays which hit the background, and the three light sources cause a large number of shadow rays to be generated. gears: This database consists of a set of meshed gears. Some of the gears are transmitters, making this database lengthy to render. The gear faces each have 144 vertices, and thus tests polygon inside/outside test efficiency. Depth complexity is medium. mount: The fractal mountain generator is derived from Loren Carpenter's method, and the composition with the four glass spheres is inspired by Peter Watterberg's work. Most objects are tiny (i.e. fractal facets), but rendering time is dominated by the rendering of the four large spheres. Depth complexity is low, and there is much background area. rings: Objects with six pentagonal rings form a pyramid against a background polygon. With a high amount of interreflection and shadowing, this scene is fairly lengthy to render. Depth complexity is also high, with all of the objects partially or fully obscured. teapot: The famous teapot on a checkerboard. There are a number of variations on the teapot database, i.e. whether the bottom is included (the IEEE CG&A article added a bottom), variations in the control points on the lid (which creates thin, almost degenerate triangles), etc. For this database generator, the bottom is created, and the degenerate polygonal patches at the center of the lid and bottom are not output. The bottom of the teapot is not flat, interestingly enough. The resolution of the checkerboard shows the resolution of the teapot meshing (with each teapot quadrilateral cut into two triangles), e.g. an 8x8 checkerboard means that 8x8x2 triangles are generated per patch. The definitions for the 32 Bezier patches are a part of the program. All objects are reflective and there are two light sources. Depth complexity is low. tetra: A recursive tetrahedral pyramid, first visualized by Benoit Mandelbrot and Alan Norton. This scene is dominated by background (around 80%). With the objects not being reflective and there being only one light source, this database is particularly quick to render, with various forms of coherency being very useful. Depth complexity is medium, though some rays must pass by many triangles for some of the background pixels. tree: A tree formed using Aono and Kunii's tree generation method. With seven light sources, the emphasis is on shadow testing. Shadow caching yields little improvement due to the narrow primitives, and many shadow rays pass through complex areas without hitting any objects. There is a fair amount of background area. Depth complexity is low. balls gears mount rings ----- ----- ----- ----- primitives SP P PS YSP total prim. 7382 9345 8196 8401 poly/patches 1417K 9345 8960 874K lights 3 5 1 3 background 0% 7% 34% 0% specular yes yes yes yes transmitter no yes yes no eye hit rays 263169 245086 173125 263169 reflect rays 175095 304643 354769 315236 refract rays 0 207564 354769 0 shadow rays 954368 2246955 412922 1085002 teapot tetra tree ------ ----- ---- primitives TP P OSP total prim. 9264 4096 8191 poly/patches 9264 4096 852K lights 2 1 7 background 39% 81% 35% reflector yes no no transmitter no no no eye hit rays 161120 49788 169836 reflect rays 225248 0 0 refract rays 0 0 0 shadow rays 407656 46112 1097419 "primitives" are S=sphere, P=polygon, T=polygonal patch, Y=cylinder, O=cone, listed from most in database to least. "total prim." is the total number of ray-tracing primitives (polygons, spheres, cylinders and cones) in the scene. The number of polygons and vectors generated is a function of the OUTPUT_RESOLUTION. The default value for this parameter is 4 for all databases. "poly/patches" is the total number of polygons and polygonal patches generated when using OUTPUT_PATCHES. "lights" is simply the number of lights in a scene. "background" is the percentage of background color (empty space) seen directly by the eye for the given view. "reflector" tells if there are reflective objects in the scene, and "transmitter" if there are transparent objects. "eye hit rays" is the number of rays from the eye which actually hit an object (i.e. not the background). 513x513 eye rays are assumed to be shot (i.e. one ray per pixel corner). "reflect rays" is the total number of rays generated by reflection off of reflecting and transmitting surfaces. "refract rays" is the number of rays generated by transmitting surfaces. "shadow rays" is the sum total of rays shot towards the lights. Note that if a surface is facing away from a light, or the background is hit, a light ray is not formed. The numbers given can vary noticeably from a given ray tracer, but should all be within about 10%. "K" means exactly 1000 (not 1024), with number rounded to the nearest K. All of the above statistics should be approximately the same for all classical ray tracers. Testing Procedures ------------------ Below are listed the requirements for testing various algorithms. These test conditions should be realizable by most renderers, and are meant to represent a common mode of operation for each algorithm. Special features which the software supports (or standard features which it lacks) should be noted in your statistics. 1) The non-polygon (OUTPUT_CURVES) format should normally be used for ray-tracing tests. 2) All opaque (non-transmitting) primitives can be considered one-sided for rendering purposes. Only the outside of primitives are visible in the scenes. The only exception to this is the "teapot" database, in which the teapot itself should normally be double sided (this is necessary because the lid of the teapot does not fit tightly, allowing the viewer to see back faces). 3) Polygonal patches (which are always triangles in the SPD) should have smooth shading, if available. 4) Specular highlighting should be performed for surfaces with a reflective component. The simple Phong distribution model is sufficient. 5) Light sources are positional. If unavailable, assign the directional lights a vector given by the light position and the viewing "lookat" position. 6) Render at a resolution of 512 x 512 pixels, shooting rays at the corners (meaning that 513 x 513 eye rays will be created). The four corner contributions are averaged to arrive at a pixel value. If rendering is done differently, note this fact. No pixel subdivision is performed. 7) The maximum tree depth is 5 (where the eye ray is of depth 1). Beyond this depth rays do not have to be spawned. 8) All rays hitting only reflective and transmitting objects spawn reflection rays, unless the maximum ray depth was reached by the spawning ray. No adaptive tree depth cutoff is allowed; that is, all rays must be spawned (adaptive tree depth is a proven time saver and is also dependent on the color model used - see Roy Hall's work for details). 9) All rays hitting transmitting objects spawn refraction rays, unless the maximum ray depth was reached or total internal reflection occurs. Transmitting rays should be refracted using Snell's Law (i.e. should not pass straight through an object). If total internal reflection occurs, a reflection ray should still be generated at this node. Note that all transmitters in the SPD are also reflective, but this is not a requirement of the file format itself. 10) A shadow ray is not generated if the surface normal points away from the light. This is true even on transmitting surfaces. Note any changes from this condition. 11) Assume no hierarchy is given with the database (for example, color change cannot be used to note a clustering). The ray tracing program itself can create its own hierarchy, but this process should be automatic. Note any exceptions to this (e.g. not including the background polygon in the efficiency structure, changing the background polygon into an infinite plane, etc). Such changes can be critical for the efficiency of some schemes, so an explanation of why changes were made is important. 12) Timing costs should be separated into at least two areas: preprocessing and ray-tracing. Preprocessing includes all time spent initializing, reading the database, and creating data structures needed to ray-trace. Preprocessing should be all the constant cost operations--those that do not change with the resolution of the image. Ray-tracing is the time actually spent tracing the rays (i.e. everything that is not preprocessing). 13) Other timing costs which would be of interest are in a breakdown of times spent in preprocessing and during actual ray-tracing. Examples include time spent reading in the data itself, creating a hierarchy, octree, or item buffer, and times spent on intersection the various primitives and on calculating the shade. 14) Time-independent statistics on the performance of the algorithm should be gathered. Some examples are the number of ray/object intersection tests, the number of ray/object tests which actually hit objects, number of octree or grid nodes accessed, and the number of successful shadow cache hits. Timings ------- Rendering time of the ray-traced test set on an HP-835, optimized (512 x 512): Input Setup Ray-Tracing | Polygon Sphere Cyl/Cone Bounding (hr:min:sec) | Tests Tests Tests Box Tests ------------------------------------------------------------------------------- balls 0:14 0:19 24:56 | 822K 6197K 0 51726K gears 0:56 0:18 1:02:31 | 13703K 0 0 107105K mount 0:31 0:14 18:49 | 4076K 3978K 0 31106K rings 0:41 0:33 53:41 | 1045K 5315K 16298K 91591K teapot 1:02 0:18 25:38 | 7281K 0 0 57050K tetra 0:15 0:06 3:48 | 965K 0 0 7637K tree 0:40 0:31 11:36 | 479K 524K 1319K 22002K Input: time spent reading in the NFF file. Setup: time spent creating the database and any ray tracing efficiency structures, and cleaning up after ray trace (does not include "Input" time). Ray-Tracing: time spent traversing and rendering the pixel grid. A typical set of ray tracing intersection statistics for the tetra database is: [these statistics should be the same for all users] image size: 512 x 512 total number of pixels: 262144 [ 512 x 512 ] total number of trees generated: 263169 [ 513 x 513 ] total number of tree rays generated: 263169 [ no rays spawned ] number of eye rays which hit background: 213381 [ 81% - might vary ] average number of rays per tree: 1.000000 average number of rays per pixel: 1.003910 total number of shadow rays generated: 46111 [ might vary a bit ] [these tests vary depending on the ray-tracing algorithm used] Intersector performance Bounding box intersections: 7636497 - 26.71 usec/test Polygon intersections: 964567 - 36.77 usec/test Ray generation Eye rays generated: 263169 ( 49788 hit - 18.92% ) Reflection rays generated: 0 Refraction rays generated: 0 Shadow rays generated: 46111 Coherency hits: 3407 - 7.39 % of total Fully tested: 42704 The ray-tracer which generated these statistics is based on hierarchical bounding boxes generated using Goldsmith & Salmon's automatic hierarchy method (see IEEE CG&A May 1987). It no longer uses an item buffer, hence the higher number of overall intersection tests from earlier SPD versions. One problem worth analyzing when using the SPD for efficiency tests is how octree, SEADS, and other space dividing algorithms perform when the background polygon dimensions are changed (thus changing the size of the outermost enclosing box, which changes the encoding of the environment). One analysis of the effect of the background polygon on RayShade can be found in "Ray Tracing News", volume 3, number 1. Future Work ----------- These databases are not meant to be the ultimate in standards, but are presented as an attempt at providing representative modeled environments. A number of extensions to the file format could be provided someday, along with new database generators which use them. The present databases do not contain polygons with holes, spline patches, polygonal mesh, triangular strip, or polyhedron data structures. Modeling matrices are not output, and CSG combined primitives are not included. Light sources are particularly simplistic. For a richer, more user-friendly scene description language, take a look at RayShade or RenderMan. As far as database geometry is concerned, most scenes have a preponderance of small primitives. If you find that these databases do not reflect the type of environments you render, please write and explain why (or better yet, write one or more programs that will generate your "typical" environments--maybe it will get put in the next release). Acknowledgements ---------------- I originally heard of the idea of standard scenes from Don Greenberg back in 1984. Some time earlier he and Ed Catmull had talked over coming up with some standard databases for testing algorithmic claims, and to them must go the credit for the basic concept. The idea of making small programs which generate the data came to me after Tim Kay generously sent huge files of his tree database via email - I felt there had to be a better way. Adding the teapot was inspired by the repeated demand on comp.graphics for this database, certainly the most famous of all. Many thanks to the reviewers, listed alphabetically: Kells Elmquist, Jeff Goldsmith, Donald Greenberg, David Hook, Craig Kolb, Susan Spach, Rick Speer, K.R. Subramanian, J. Eric Townsend, Mark VandeWettering, John Wallace, Greg Ward, and Louise Watson. Other people who have kindly offered their ideas and opinions on this project include Brian Barsky, Andrew Glassner, Roy Hall, Chip Hatfield, Tim Kay, John Recker, Paul Strauss, and Chan Verbeck. These names are mentioned mostly as a listing of people interested in this idea. They do not necessarily agree (and in some cases strongly disagree) with the validity of the concept or the choice of databases. Your comments and suggestions on these databases are appreciated. Please do send me any timing results for software and hardware which you test, or any publications which use the SPD package.