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root/radiance/ray/doc/ray.1
Revision: 1.2
Committed: Tue Mar 11 19:29:04 2003 UTC (21 years, 7 months ago) by greg
Branch: MAIN
Changes since 1.1: +2 -0 lines
Log Message:
Changed alias handling to allow tracking, fixed freeobjects() and do_irrad bugs

File Contents

# Content
1 .\" RCSid "$Id"
2 .\" Print using the -ms macro package
3 .DA 1/20/99
4 .LP
5 .tl """Copyright \(co 1996 Regents, University of California
6 .sp 2
7 .TL
8 The
9 .so ../src/rt/VERSION
10 .br
11 Synthetic Imaging System
12 .AU
13 Greg Ward
14 .br
15 Lawrence Berkeley Laboratory
16 .br
17 1 Cyclotron Rd.
18 .br
19 Berkeley, CA 94720
20 .br
21 (510) 486-4757
22 .NH 1
23 Introduction
24 .PP
25 RADIANCE was developed as a research tool
26 for predicting the distribution of visible radiation in
27 illuminated spaces.
28 It takes as input a three-dimensional geometric model of
29 the physical environment, and produces a map of
30 spectral radiance values in a color image.
31 The technique of ray-tracing follows light backwards
32 from the image plane to the source(s).
33 Because it can produce realistic images from a simple description,
34 RADIANCE has a wide range of applications in graphic arts,
35 lighting design, computer-aided engineering and architecture.
36 .KF
37 .sp 25
38 .ce
39 .B "Figure 1."
40 .sp
41 .KE
42 .PP
43 The diagram in Figure 1 shows the flow between programs (boxes) and
44 data (ovals).
45 The central program is
46 .I rpict,
47 which produces a picture from a scene description.
48 .I Rview
49 is a variation of
50 .I rpict
51 that computes and displays images interactively.
52 .PP
53 A scene description file lists the surfaces and materials
54 that make up a specific environment.
55 The current surface types are spheres, polygons, cones,
56 and cylinders.
57 They can be made from materials such as plastic, metal,
58 and glass.
59 Light sources can be distant disks as well as local spheres, discs and
60 polygons.
61 .PP
62 From a three-dimensional scene description and a specified view,
63 .I rpict
64 produces a two-dimensional image.
65 A picture file is a compressed binary representation of the
66 pixels in the image.
67 This picture can be scaled in size and
68 brightness, anti-aliased, and sent to a graphics output device.
69 .PP
70 A header in each picture file lists the program(s) and
71 parameters that produced it.
72 This is useful for identifying a picture
73 without having to display it.
74 The information can be read by the program
75 .I getinfo.
76 .NH 1
77 Scene Description
78 .PP
79 A scene description file represents a
80 three-dimensional physical environment
81 in Cartesian (rectilinear) world coordinates.
82 It is stored as ASCII text, with the following basic format:
83 .DS
84 # comment
85
86 modifier type identifier
87 n S1 S2 S3 .. Sn
88 0
89 m R1 R2 R3 .. Rm
90
91 modifier alias identifier reference
92
93 ! command
94
95 ...
96 .DE
97 .PP
98 A comment line begins with a pound sign, `#'.
99 .PP
100 The scene description
101 .I primitives
102 all have the same general format, and can
103 be either surfaces or modifiers.
104 A primitive has a modifier, a type, and an identifier.
105 A modifier is either the identifier of a
106 .I "previously defined"
107 primitive, or "void"\(dg.
108 .FS
109 \(dgThe most recent definition of a modifier is the one used,
110 and later definitions do not cause relinking of loaded
111 primitives.
112 Thus, the same identifier may be used repeatedly, and each new
113 definition will apply to the primitives following it.
114 .FE
115 An identifier can be any string (i.e. sequence of non-blank
116 characters).
117 The
118 .I arguments
119 associated with a primitive can be strings or real numbers.
120 The first integer following the identifier is the number
121 of string arguments, and it is followed by the arguments themselves
122 (separated by white space).
123 The next integer is the number of integer arguments, and is followed
124 by the integer arguments.
125 (There are currently no primitives that use them, however.)
126 The next integer is the real argument count, and it is followed
127 by the real arguments.
128 .PP
129 An alias gets its type and arguments from a previously defined primitive.
130 This is useful when the same material is used with a different
131 modifier, or as a convenient naming mechanism.
132 The reserved modifier name "inherit" may be used to specificy that
133 an alias will inherit its modifier from the original.
134 Surfaces cannot be aliased.
135 .PP
136 A line beginning with an exclamation point, `!',
137 is interpreted as a command.
138 It is executed by the shell, and its output is read as input to
139 the program.
140 The command must not try to read from its standard input, or
141 confusion will result.
142 A command may be continued over multiple lines using a backslash, `\\',
143 to escape the newline.
144 .PP
145 Blank space is generally ignored, except as a separator.
146 The exception is the newline character after a command or comment.
147 Commands, comments and primitives may appear in any combination, so long
148 as they are not intermingled.
149 .NH 2
150 Primitive Types
151 .PP
152 Primitives can be surfaces, materials, textures or patterns.
153 Modifiers can be materials, textures or patterns.
154 Simple surfaces must have one material in their modifier list.
155 .NH 3
156 Surfaces
157 .PP
158 A scene description will consist mostly of surfaces.
159 The basic types are given below.
160 .LP
161 .UL Source
162 .PP
163 A source is not really a surface, but a solid angle.
164 It is used for specifying light sources that are very distant.
165 The direction to the center of the source and the number of degrees
166 subtended by its disk are given as follows:
167 .DS
168 mod source id
169 0
170 0
171 4 xdir ydir zdir angle
172 .DE
173 .LP
174 .UL Sphere
175 .PP
176 A sphere is given by its center and radius:
177 .DS
178 mod sphere id
179 0
180 0
181 4 xcent ycent zcent radius
182 .DE
183 .LP
184 .UL Bubble
185 .PP
186 A bubble is simply a sphere whose surface normal points inward.
187 .LP
188 .UL Polygon
189 .PP
190 A polygon is given by a list of three-dimensional vertices,
191 which are ordered counter-clockwise as viewed from
192 the front side (into the surface normal).
193 The last vertex is automatically connected to the first.
194 Holes are represented in polygons as interior vertices connected to
195 the outer perimeter by coincident edges (seams).
196 .DS
197 mod polygon id
198 0
199 0
200 3n
201 x1 y1 z1
202 x2 y2 z2
203 ...
204 xn yn zn
205 .DE
206 .LP
207 .UL Cone
208 .PP
209 A cone is a megaphone-shaped object.
210 It is truncated by two planes perpendicular to its axis,
211 and one of its ends may come to a point.
212 It is given as two axis endpoints, and the starting
213 and ending radii:
214 .DS
215 mod cone id
216 0
217 0
218 8
219 x0 y0 z0
220 x1 y1 z1
221 r0 r1
222 .DE
223 .LP
224 .UL Cup
225 .PP
226 A cup is an inverted cone (i.e. has an inward surface normal).
227 .LP
228 .UL Cylinder
229 .PP
230 A cylinder is like a cone, but its starting and ending radii are
231 equal.
232 .DS
233 mod cylinder id
234 0
235 0
236 7
237 x0 y0 z0
238 x1 y1 z1
239 rad
240 .DE
241 .LP
242 .UL Tube
243 .PP
244 A tube is an inverted cylinder.
245 .LP
246 .UL Ring
247 .PP
248 A ring is a circular disk given by its center, surface
249 normal, and inner and outer radii:
250 .DS
251 mod ring id
252 0
253 0
254 8
255 xcent ycent zcent
256 xdir ydir zdir
257 r0 r1
258 .DE
259 .LP
260 .UL Mesh
261 .PP
262 A mesh is a compound surface, made up of many triangles and
263 an octree data structure to accelerate ray intersection.
264 It is typically converted from a Wavefront .OBJ file using the
265 obj2mesh program.
266 .DS
267 mod mesh id
268 1+ meshfile transform
269 0
270 0
271 .DE
272 The transform moves the mesh to the desired location in the scene.
273 Multiple instances using the same meshfile take little extra memory,
274 and the compiled mesh itself takes much less space than individual
275 polygons would.
276 In the case of an unsmoothed mesh, using the mesh primitive reduces
277 memory requirements by a factor of 30 relative to individual triangles.
278 If a mesh has smoothed surfaces, we save a factor of 50 or more,
279 permitting very detailed geometries that would otherwise exhaust the
280 available memory.
281 In addition, the mesh primitive can have associated (u,v) coordinates
282 for pattern and texture mapping.
283 These are made available to function files via the Lu and Lu variables.
284 .LP
285 .UL Instance
286 .PP
287 An instance is a compound surface, given by the contents of an
288 octree file (created by oconv).
289 .DS
290 mod instance id
291 1+ octree transform
292 0
293 0
294 .DE
295 If the modifier is "void", then surfaces will use the modifiers given
296 in the original description.
297 Otherwise, the modifier specified is used in their place.
298 The transform moves the octree to the desired location in the scene.
299 Multiple instances using the same octree take little extra memory,
300 hence very complex descriptions can be rendered using this primitive.
301 .PP
302 There are a number of important limitations to be aware of when using
303 instances.
304 First, the scene description used to generate the octree must stand on
305 its own, without referring to modifiers in the parent description.
306 This is necessary for oconv to create the octree.
307 Second, light sources in the octree will not be incorporated correctly
308 in the calculation, and they are not recommended.
309 Finally, there is no advantage (other than convenience) to
310 using a single instance of an octree, or an octree containing only a
311 few surfaces.
312 An xform command on the subordinate description is prefered in such cases.
313 .NH 3
314 Materials
315 .PP
316 A material defines the way light interacts with a surface.
317 The basic types are given below.
318 .LP
319 .UL Light
320 .PP
321 Light is the basic material for self-luminous surfaces (i.e. light
322 sources).
323 In addition to the source surface type, spheres, discs (rings with zero
324 inner radius), cylinders (provided they are long enough), and
325 polygons can act as light sources.
326 Polygons work best when they are rectangular.
327 Cones cannot be used at this time.
328 A pattern may be used to specify a light output distribution.
329 Light is defined simply as a RGB radiance value (watts/steradian/m2):
330 .DS
331 mod light id
332 0
333 0
334 3 red green blue
335 .DE
336 .LP
337 .UL Illum
338 .PP
339 Illum is used for secondary light sources with broad distributions.
340 A secondary light source is treated like any other
341 light source, except when viewed directly.
342 It then acts like it is made of a different material (indicated by
343 the string argument), or becomes invisible (if no string argument is given,
344 or the argument is "void").
345 Secondary sources are useful when modeling windows or
346 brightly illuminated surfaces.
347 .DS
348 mod illum id
349 1 material
350 0
351 3 red green blue
352 .DE
353 .LP
354 .UL Glow
355 .PP
356 Glow is used for surfaces that are self-luminous, but limited
357 in their effect.
358 In addition to the radiance value, a maximum radius for
359 shadow testing is given:
360 .DS
361 mod glow id
362 0
363 0
364 4 red green blue maxrad
365 .DE
366 If maxrad is zero, then the surface will never be tested
367 for shadow, although it may participate in an interreflection calculation.
368 If maxrad is negative, then the surface will never contribute to scene
369 illumination.
370 Glow sources will never illuminate objects on the other side of an
371 illum surface.
372 This provides a convenient way to illuminate local light fixture
373 geometry without overlighting nearby objects.
374 .LP
375 .UL Spotlight
376 .PP
377 Spotlight is used for self-luminous surfaces having directed output.
378 As well as radiance, the full cone angle (in degrees)
379 and orientation (output direction) vector are given.
380 The length of the orientation vector is the distance
381 of the effective focus behind the source center (i.e. the focal length).
382 .DS
383 mod spotlight id
384 0
385 0
386 7 red green blue angle xdir ydir zdir
387 .DE
388 .LP
389 .UL Mirror
390 .PP
391 Mirror is used for planar surfaces that produce secondary
392 source reflections.
393 This material should be used sparingly, as it may cause the light
394 source calculation to blow up if it is applied to many small surfaces.
395 This material is only supported for flat surfaces such as polygons
396 and rings.
397 The arguments are simply the RGB reflectance values, which should be
398 between 0 and 1.
399 An optional string argument may be used like the illum type to specify a
400 different material to be used for shading non-source rays.
401 If this alternate material is given as "void", then the mirror surface
402 will be invisible.
403 This is only appropriate if the surface hides other (more detailed)
404 geometry with the same overall reflectance.
405 .DS
406 mod mirror id
407 1 material
408 0
409 3 red green blue
410 .DE
411 .LP
412 .UL Prism1
413 .PP
414 The prism1 material is for general light redirection from prismatic
415 glazings, generating secondary light sources.
416 It can only be used to modify a planar surface (i.e. a polygon or disk)
417 and should not result in either light concentration or scattering.
418 The new direction of the ray can be on either side of the material,
419 and the definitions must have the correct bidirectional properties
420 to work properly with secondary light sources.
421 The arguments give the coefficient for the redirected light
422 and its direction.
423 .DS
424 mod prism1 id
425 5+ coef dx dy dz funcfile transform
426 0
427 n A1 A2 .. An
428 .DE
429 The new direction variables
430 .I "dx, dy"
431 and
432 .I dz
433 need not produce a normalized vector.
434 For convenience, the variables
435 .I "DxA, DyA"
436 and
437 .I DzA
438 are defined as the normalized direction to the target light source.
439 See section 2.2.1 on function files for further information.
440 .LP
441 .UL Prism2
442 .PP
443 The material prism2 is identical to prism1 except that
444 it provides for two ray redirections rather than one.
445 .DS
446 mod prism2 id
447 9+ coef1 dx1 dy1 dz1 coef2 dx2 dy2 dz2 funcfile transform
448 0
449 n A1 A2 .. An
450 .DE
451 .LP
452 .UL Mist
453 .PP
454 Mist is a virtual material used to delineate a volume
455 of participating atmosphere.
456 A list of important light sources may be given, along with an
457 extinction coefficient, scattering albedo and scattering eccentricity
458 parameter.
459 The light sources named by the string argument list
460 will be tested for scattering within the volume.
461 Sources are identified by name, and virtual light sources may be indicated
462 by giving the relaying object followed by '>' followed by the source, i.e:
463 .DS
464 3 source1 mirror1>source10 mirror2>mirror1>source3
465 .DE
466 Normally, only one source is given per mist material, and there is an
467 upper limit of 32 to the total number of active scattering sources.
468 The extinction coefficient, if given, is added to the global
469 coefficient set on the command line.
470 Extinction is in units of 1/distance (distance based on the world coordinates),
471 and indicates the proportional loss of radiance over one unit distance.
472 The scattering albedo, if present, will override the global setting within
473 the volume.
474 An albedo of 0\00\00 means a perfectly absorbing medium, and an albedo of
475 1\01\01\0 means
476 a perfectly scattering medium (no absorption).
477 The scattering eccentricity parameter will likewise override the global
478 setting if it is present.
479 Scattering eccentricity indicates how much scattered light favors the
480 forward direction, as fit by the Heyney-Greenstein function:
481 .DS
482 P(theta) = (1 - g*g) / (1 + g*g - 2*g*cos(theta))^1.5
483 .DE
484 A perfectly isotropic scattering medium has a g parameter of 0, and
485 a highly directional material has a g parameter close to 1.
486 Fits to the g parameter may be found along with typical extinction
487 coefficients and scattering albedos for various atmospheres and
488 cloud types in USGS meteorological tables.
489 (A pattern will be applied to the extinction values.)\0
490 .DS
491 mod mist id
492 N src1 src2 .. srcN
493 0
494 0|3|6|7 [ rext gext bext [ ralb galb balb [ g ] ] ]
495 .DE
496 There are two usual uses of the mist type.
497 One is to surround a beam from a spotlight or laser so that it is
498 visible during rendering.
499 For this application, it is important to use a cone (or cylinder) that
500 is long enough and wide enough to contain the important visible portion.
501 Light source photometry and intervening objects will have the desired
502 effect, and crossing beams will result in additive scattering.
503 For this application, it is best to leave off the real arguments, and
504 use the global rendering parameters to control the atmosphere.
505 The second application is to model clouds or other localized media.
506 Complex boundary geometry may be used to give shape to a uniform medium,
507 so long as the boundary encloses a proper volume.
508 Alternatively, a pattern may be used to set the line integral value
509 through the cloud for a ray entering or exiting a point in a given
510 direction.
511 For this application, it is best if cloud volumes do not overlap each other,
512 and opaque objects contained within them may not be illuminated correctly
513 unless the line integrals consider enclosed geometry.
514 .LP
515 .UL Plastic
516 .PP
517 Plastic is a material with uncolored highlights.
518 It is given by its RGB reflectance, its fraction of specularity,
519 and its roughness value.
520 Roughness is specified as the rms slope of surface facets.
521 A value of 0 corresponds to a perfectly smooth surface, and
522 a value of 1 would be a very rough surface.
523 Specularity fractions greater than 0.1 and
524 roughness values greater than 0.2 are not very
525 realistic.
526 (A pattern modifying plastic will affect the material color.)
527 .DS
528 mod plastic id
529 0
530 0
531 5 red green blue spec rough
532 .DE
533 .LP
534 .UL Metal
535 .PP
536 Metal is similar to plastic, but specular highlights
537 are modified by the material color.
538 Specularity of metals is usually .9 or greater.
539 As for plastic, roughness values above .2 are uncommon.
540 .LP
541 .UL Trans
542 .PP
543 Trans is a translucent material, similar to plastic.
544 The transmissivity is the fraction of penetrating light that
545 travels all the way through the material.
546 The transmitted specular component is the fraction of transmitted
547 light that is not diffusely scattered.
548 Transmitted and diffusely reflected light is modified by the material color.
549 Translucent objects are infinitely thin.
550 .DS
551 mod trans id
552 0
553 0
554 7 red green blue spec rough trans tspec
555 .DE
556 .LP
557 .UL Plastic2
558 .PP
559 Plastic2 is similar to plastic, but with anisotropic
560 roughness.
561 This means that highlights in the surface will appear elliptical rather
562 than round.
563 The orientation of the anisotropy is determined by the unnormalized
564 direction vector
565 .I "ux uy uz".
566 These three expressions (separated by white space) are evaluated in
567 the context of the function file
568 .I funcfile.
569 If no function file is required (i.e. no special variables or
570 functions are required), a period (`.') may be given in its
571 place.
572 (See the discussion of Function Files in the Auxiliary Files section).
573 The
574 .I urough
575 value defines the roughness along the
576 .B u
577 vector given projected onto the surface.
578 The
579 .I vrough
580 value defines the roughness perpendicular to this vector.
581 Note that the highlight will be narrower in the direction of the
582 smaller roughness value.
583 Roughness values of zero are not allowed for efficiency reasons
584 since the behavior would be the same as regular plastic in that
585 case.
586 .DS
587 mod plastic2 id
588 4+ ux uy uz funcfile transform
589 0
590 6 red green blue spec urough vrough
591 .DE
592 .LP
593 .UL Metal2
594 .PP
595 Metal2 is the same as plastic2, except that the highlights are
596 modified by the material color.
597 .LP
598 .UL Trans2
599 .PP
600 Trans2 is the anisotropic version of trans.
601 The string arguments are the same as for plastic2, and the real
602 arguments are the same as for trans but with an additional roughness
603 value.
604 .DS
605 mod trans2 id
606 4+ ux uy uz funcfile transform
607 0
608 8 red green blue spec urough vrough trans tspec
609 .DE
610 .LP
611 .UL Dielectric
612 .PP
613 A dielectric material is transparent, and it refracts light
614 as well as reflecting it.
615 Its behavior is determined by the index of refraction and
616 transmission coefficient in each wavelength band per unit length.
617 Common glass has a index of refraction (n) around 1.5,
618 and a transmission coefficient of roughly 0.92 over an inch.
619 An additional number, the Hartmann constant, describes how
620 the index of refraction changes as a function of wavelength.
621 It is usually zero.
622 (A pattern modifies only the refracted value.)
623 .DS
624 mod dielectric id
625 0
626 0
627 5 rtn gtn btn n hc
628 .DE
629 .LP
630 .UL Interface
631 .PP
632 An interface is a boundary between two dielectrics.
633 The first transmission coefficient and refractive index are for the inside;
634 the second ones are for the outside.
635 Ordinary dielectrics are surrounded by a vacuum (1 1 1 1).
636 .DS
637 mod interface id
638 0
639 0
640 8 rtn1 gtn1 btn1 n1 rtn2 gtn2 btn2 n2
641 .DE
642 .LP
643 .UL Glass
644 .PP
645 Glass is similar to dielectric, but it is optimized for thin glass
646 surfaces (n = 1.52).
647 One transmitted ray and one reflected ray is produced.
648 By using a single surface is in place of two, internal reflections
649 are avoided.
650 The surface orientation is irrelevant, as it is for plastic,
651 metal, and trans.
652 The only specification required is the transmissivity at normal
653 incidence.
654 (Transmissivity is the amount of light not absorbed in one traversal
655 of the material.
656 Transmittance -- the value usually measured -- is the total light
657 transmitted through the pane including multiple reflections.)\0
658 To compute transmissivity (tn) from transmittance (Tn) use:
659 .DS
660 tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn
661 .DE
662 Standard 88% transmittance glass has a transmissivity of 0.96.
663 (A pattern modifying glass will affect the transmissivity.)
664 If a fourth real argument is given, it is interpreted as the index of
665 refraction to use instead of 1.52.
666 .DS
667 mod glass id
668 0
669 0
670 3 rtn gtn btn
671 .DE
672 .LP
673 .UL Plasfunc
674 .PP
675 Plasfunc in used for the procedural definition of plastic-like
676 materials with arbitrary bidirectional reflectance distribution
677 functions (BRDF's).
678 The arguments to this material include the color and specularity,
679 as well as the function defining the specular distribution and the
680 auxiliary file where it may be found.
681 .DS
682 mod plasfunc id
683 2+ refl funcfile transform
684 0
685 4+ red green blue spec A5 ..
686 .DE
687 The function
688 .I refl
689 takes four arguments, the x, y and z
690 direction towards the incident light, and the solid angle
691 subtended by the source.
692 The solid angle is provided to facilitate averaging, and is usually
693 ignored.
694 The
695 .I refl
696 function should integrate to 1 over
697 the projected hemisphere to maintain energy balance.
698 At least four real arguments must be given, and these are made
699 available along with any additional values to the reflectance
700 function.
701 Currently, only the contribution from direct light sources is
702 considered in the specular calculation.
703 As in most material types, the surface normal is always
704 altered to face the incoming ray.
705 .LP
706 .UL Metfunc
707 .PP
708 Metfunc is identical to plasfunc and takes the same arguments, but
709 the specular component is multiplied also by the material color.
710 .LP
711 .UL Transfunc
712 .PP
713 Transfunc is similar to plasfunc but with an arbitrary bidirectional
714 transmittance distribution as well as a reflectance distribution.
715 Both reflectance and transmittance are specified with the same function.
716 .DS
717 mod transfunc id
718 2+ brtd funcfile transform
719 0
720 6+ red green blue rspec trans tspec A7 ..
721 .DE
722 Where
723 .I trans
724 is the total light transmitted and
725 .I tspec
726 is the non-Lambertian fraction of transmitted light.
727 The function
728 .I brtd
729 should integrate to 1 over each projected hemisphere.
730 .LP
731 .UL BRTDfunc
732 .PP
733 The material BRTDfunc gives the maximum flexibility over surface
734 reflectance and transmittance, providing for spectrally-dependent
735 specular rays and reflectance and transmittance distribution functions.
736 .DS
737 mod BRTDfunc id
738 10+ rrefl grefl brefl
739 rtrns gtrns btrns
740 rbrtd gbrtd bbrtd
741 funcfile transform
742 0
743 9+ rfdif gfdif bfdif
744 rbdif gbdif bbdif
745 rtdif gtdif btdif
746 A10 ..
747 .DE
748 The variables
749 .I "rrefl, grefl"
750 and
751 .I brefl
752 specify the color coefficients for
753 the ideal specular (mirror) reflection of the surface.
754 The variables
755 .I "rtrns, gtrns"
756 and
757 .I btrns
758 specify the color coefficients for the ideal specular transmission.
759 The functions
760 .I "rbrtd, gbrtd"
761 and
762 .I bbrtd
763 take the direction to the incident light (and its solid angle)
764 and compute the color coefficients for the directional diffuse part of
765 reflection and transmission.
766 As a special case, three identical values of '0' may be given in place of
767 these function names to indicate no directional diffuse component.
768 .PP
769 Unlike most other material types, the surface normal is not altered to
770 face the incoming ray.
771 Thus, functions and variables must pay attention to the orientation of
772 the surface and make adjustments appropriately.
773 However, the special variables for the perturbed dot product and surface
774 normal,
775 .I "RdotP, NxP, NyP"
776 and
777 .I NzP
778 are reoriented as if the ray hit the front surface for convenience.
779 .PP
780 A diffuse reflection component may be given for the front side with
781 .I "rfdif, gfdif"
782 and
783 .I bfdif
784 for the front side of the surface or
785 .I "rbdif, gbdif"
786 and
787 .I bbdif
788 for the back side.
789 The diffuse transmittance (must be the same for both sides by physical law)
790 is given by
791 .I "rtdif, gtdif"
792 and
793 .I btdif.
794 A pattern will modify these diffuse scattering values,
795 and will be available through the special variables
796 .I "CrP, CgP"
797 and
798 .I CbP.
799 .PP
800 Care must be taken when using this material type to produce a physically
801 valid reflection model.
802 The reflectance functions should be bidirectional, and under no circumstances
803 should the sum of reflected diffuse, transmitted diffuse, reflected specular,
804 transmitted specular and the integrated directional diffuse component be
805 greater than one.
806 .LP
807 .UL Plasdata
808 .PP
809 Plasdata is used for arbitrary BRDF's that are most conveniently
810 given as interpolated data.
811 The arguments to this material are the data file and coordinate index
812 functions, as well as a function to optionally modify the data
813 values.
814 .DS
815 mod plasdata id
816 3+n+
817 func datafile
818 funcfile x1 x2 .. xn transform
819 0
820 4+ red green blue spec A5 ..
821 .DE
822 The coordinate indices
823 .I "(x1, x2,"
824 etc.) are themselves functions of
825 the x, y and z direction to the incident light, plus the solid angle
826 subtended by the light source (usually ignored).
827 The data function
828 .I (func)
829 takes five variables, the
830 interpolated value from the n-dimensional data file, followed by the
831 x, y and z direction to the incident light and the solid angle of the source.
832 The light source direction and size may of course be ignored by the function.
833 .LP
834 .UL Metdata
835 .PP
836 As metfunc is to plasfunc, metdata is to plasdata.
837 Metdata takes the same arguments as plasdata, but the specular
838 component is modified by the given material color.
839 .LP
840 .UL Transdata
841 .PP
842 Transdata is like plasdata but the specification includes transmittance
843 as well as reflectance.
844 The parameters are as follows.
845 .DS
846 mod transdata id
847 3+n+
848 func datafile
849 funcfile x1 x2 .. xn transform
850 0
851 6+ red green blue rspec trans tspec A7 ..
852 .DE
853 .LP
854 .UL Antimatter
855 .PP
856 Antimatter is a material that can "subtract" volumes from other volumes.
857 A ray passing into an antimatter object becomes blind to all the specified
858 modifiers:
859 .DS
860 mod antimatter id
861 N mod1 mod2 .. modN
862 0
863 0
864 .DE
865 The first modifier will also be used to shade the area leaving the
866 antimatter volume and entering the regular volume.
867 If mod1 is void, the antimatter volume is completely invisible.
868 Antimatter does not work properly with the material type "trans",
869 and multiple antimatter surfaces should be disjoint.
870 The viewpoint must be outside all volumes concerned for a correct
871 rendering.
872 .NH 3
873 Textures
874 .PP
875 A texture is a perturbation of the surface normal, and
876 is given by either a function or data.
877 .LP
878 .UL Texfunc
879 .PP
880 A texfunc uses an auxiliary function file
881 to specify a procedural texture:
882 .DS
883 mod texfunc id
884 4+ xpert ypert zpert funcfile transform
885 0
886 n A1 A2 .. An
887 .DE
888 .LP
889 .UL Texdata
890 .PP
891 A texdata texture uses three data files to get the surface
892 normal perturbations.
893 The variables
894 .I xfunc,
895 .I yfunc
896 and
897 .I zfunc
898 take three arguments
899 each from the interpolated values in
900 .I xdfname,
901 .I ydfname
902 and
903 .I zdfname.
904 .DS
905 mod texdata id
906 8+ xfunc yfunc zfunc xdfname ydfname zdfname vfname x0 x1 .. xf
907 0
908 n A1 A2 .. An
909 .DE
910 .NH 3
911 Patterns
912 .PP
913 Patterns are used to modify the reflectance of materials.
914 The basic types are given below.
915 .LP
916 .UL Colorfunc
917 .PP
918 A colorfunc is a procedurally defined color pattern.
919 It is specified as follows:
920 .DS
921 mod colorfunc id
922 4+ red green blue funcfile transform
923 0
924 n A1 A2 .. An
925 .DE
926 .LP
927 .UL Brightfunc
928 .PP
929 A brightfunc is the same as a colorfunc, except it is monochromatic.
930 .DS
931 mod brightfunc id
932 2+ refl funcfile transform
933 0
934 n A1 A2 .. An
935 .DE
936 .LP
937 .UL Colordata
938 .PP
939 Colordata uses an interpolated data map to modify a material's color.
940 The map is n-dimensional, and is stored in three
941 auxiliary files, one for each color.
942 The coordinates used to look up and interpolate the data are
943 defined in another auxiliary file.
944 The interpolated data values are modified by functions of
945 one or three variables.
946 If the functions are of one variable, then they are passed the
947 corresponding color component (red or green or blue).
948 If the functions are of three variables, then they are passed the
949 original red, green, and blue values as parameters.
950 .DS
951 mod colordata id
952 7+n+
953 rfunc gfunc bfunc rdatafile gdatafile bdatafile
954 funcfile x1 x2 .. xn transform
955 0
956 m A1 A2 .. Am
957 .DE
958 .LP
959 .UL Brightdata
960 .PP
961 Brightdata is like colordata, except monochromatic.
962 .DS
963 mod brightdata id
964 3+n+
965 func datafile
966 funcfile x1 x2 .. xn transform
967 0
968 m A1 A2 .. Am
969 .DE
970 .LP
971 .UL Colorpict
972 .PP
973 Colorpict is a special case of colordata, where the pattern is
974 a two-dimensional image stored in the RADIANCE picture format.
975 The dimensions of the image data are determined by the picture
976 such that the smaller dimension is always 1, and the other
977 is the ratio between the larger and the smaller.
978 For example, a 500x338 picture would have coordinates (u,v)
979 in the rectangle between (0,0) and (1.48,1).
980 .DS
981 mod colorpict id
982 7+
983 rfunc gfunc bfunc pictfile
984 funcfile u v transform
985 0
986 m A1 A2 .. Am
987 .DE
988 .LP
989 .UL Colortext
990 .PP
991 Colortext is dichromatic writing in a polygonal font.
992 The font is defined in an auxiliary file, such as
993 .I helvet.fnt.
994 The text itself is also specified in a separate file, or
995 can be part of the material arguments.
996 The character size, orientation, aspect ratio and slant is
997 determined by right and down motion vectors.
998 The upper left origin for the text block as well as
999 the foreground and background colors
1000 must also be given.
1001 .DS
1002 mod colortext id
1003 2 fontfile textfile
1004 0
1005 15+
1006 Ox Oy Oz
1007 Rx Ry Rz
1008 Dx Dy Dz
1009 rfore gfore bfore
1010 rback gback bback
1011 [spacing]
1012 .DE
1013 or:
1014 .DS
1015 mod colortext id
1016 2+N fontfile . This is a line with N words ...
1017 0
1018 15+
1019 Ox Oy Oz
1020 Rx Ry Rz
1021 Dx Dy Dz
1022 rfore gfore bfore
1023 rback gback bback
1024 [spacing]
1025 .DE
1026 .LP
1027 .UL Brighttext
1028 .PP
1029 Brighttext is like colortext, but the writing is monochromatic.
1030 .DS
1031 mod brighttext id
1032 2 fontfile textfile
1033 0
1034 11+
1035 Ox Oy Oz
1036 Rx Ry Rz
1037 Dx Dy Dz
1038 foreground background
1039 [spacing]
1040 .DE
1041 or:
1042 .DS
1043 mod brighttext id
1044 2+N fontfile . This is a line with N words ...
1045 0
1046 11+
1047 Ox Oy Oz
1048 Rx Ry Rz
1049 Dx Dy Dz
1050 foreground background
1051 [spacing]
1052 .DE
1053 .LP
1054 By default, a uniform spacing algorithm is used that guarantees
1055 every character will appear in a precisely determined position.
1056 Unfortunately, such a scheme results in rather unattractive and difficult to
1057 read text with most fonts.
1058 The optional
1059 .I spacing
1060 value defines the distance between characters for proportional spacing.
1061 A positive value selects a spacing algorithm that preserves right margins and
1062 indentation, but does not provide the ultimate in proportionally spaced text.
1063 A negative value insures that characters are properly spaced, but the
1064 placement of words then varies unpredictably.
1065 The choice depends on the relative importance of spacing versus formatting.
1066 When presenting a section of formatted text, a positive spacing value is
1067 usually preferred.
1068 A single line of text will often be accompanied by a negative spacing value.
1069 A section of text meant to depict a picture, perhaps using a special purpose
1070 font such as hexbit4x1.fnt, calls for uniform spacing.
1071 Reasonable magnitudes for proportional spacing are
1072 between 0.1 (for tightly spaced characters) and 0.3 (for wide spacing).
1073 .NH 3
1074 Mixtures
1075 .PP
1076 A mixture is a blend of one or more materials or textures and patterns.
1077 The basic types are given below.
1078 .LP
1079 .UL Mixfunc
1080 .PP
1081 A mixfunc mixes two modifiers procedurally.
1082 It is specified as follows:
1083 .DS
1084 mod mixfunc id
1085 4+ foreground background vname funcfile transform
1086 0
1087 n A1 A2 .. An
1088 .DE
1089 Foreground and background are modifier names that must be
1090 defined earlier in the scene description.
1091 If one of these is a material, then
1092 the modifier of the mixfunc must be "void".
1093 (Either the foreground or background modifier may be "void",
1094 which serves as a form of opacity control when used with a material.)\0
1095 Vname is the coefficient defined in funcfile that determines the influence
1096 of foreground.
1097 The background coefficient is always (1-vname).
1098 Since the references are not resolved until runtime, the last
1099 definitions of the modifier id's will be used.
1100 This can result in modifier loops, which are detected by the
1101 renderer.
1102 .LP
1103 .UL Mixdata
1104 .PP
1105 Mixdata combines two modifiers using an auxiliary data file:
1106 .DS
1107 mod mixdata id
1108 5+n+
1109 foreground background func datafile
1110 funcfile x1 x2 .. xn transform
1111 0
1112 m A1 A2 .. Am
1113 .DE
1114 .LP
1115 .UL Mixpict
1116 .PP
1117 Mixpict combines two modifiers based on a picture:
1118 .DS
1119 mod mixpict id
1120 7+
1121 foreground background func pictfile
1122 funcfile u v transform
1123 0
1124 m A1 A2 .. Am
1125 .DE
1126 The mixing coefficient function "func" takes three
1127 arguments, the red, green and blue values
1128 corresponding to the pixel at (u,v).
1129 .LP
1130 .UL Mixtext
1131 .PP
1132 Mixtext uses one modifier for the text foreground, and one for the
1133 background:
1134 .DS
1135 mod mixtext id
1136 4 foreground background fontfile textfile
1137 0
1138 9+
1139 Ox Oy Oz
1140 Rx Ry Rz
1141 Dx Dy Dz
1142 [spacing]
1143 .DE
1144 or:
1145 .DS
1146 mod mixtext id
1147 4+N
1148 foreground background fontfile .
1149 This is a line with N words ...
1150 0
1151 9+
1152 Ox Oy Oz
1153 Rx Ry Rz
1154 Dx Dy Dz
1155 [spacing]
1156 .DE
1157 .NH 2
1158 Auxiliary Files
1159 .PP
1160 Auxiliary files used in textures and patterns
1161 are accessed by the programs during image generation.
1162 These files may be located in the working directory, or in
1163 a library directory.
1164 The environment variable
1165 .I RAYPATH
1166 can be assigned an alternate set of search directories.
1167 Following is a brief description of some common file types.
1168 .NH 3
1169 Function Files
1170 .PP
1171 A function file contains the definitions of variables, functions
1172 and constants used by a primitive.
1173 The transformation that accompanies the file name contains the necessary
1174 rotations, translations and scalings to bring the coordinates of
1175 the function file into agreement with the world coordinates.
1176 The transformation specification is the same as for the
1177 .I xform
1178 command.
1179 An example function file is given below:
1180 .DS
1181 {
1182 This is a comment, enclosed in curly braces.
1183 {Comments can be nested.}
1184 }
1185 { standard expressions use +,-,*,/,^,(,) }
1186 vname = Ny * func(A1) ;
1187 { constants are defined with a colon }
1188 const : sqrt(PI/2) ;
1189 { user-defined functions add to library }
1190 func(x) = 5 + A1*sin(x/3) ;
1191 { functions may be passed and recursive }
1192 rfunc(f,x) = if(x,f(x),f(-x)*rfunc(f,x+1)) ;
1193 { constant functions may also be defined }
1194 cfunc(x) : 10*x / sqrt(x) ;
1195 .DE
1196 Many variables and functions are already defined by the program,
1197 and they are listed in the file
1198 .I rayinit.cal.
1199 The following variables are particularly important:
1200 .DS
1201 Dx, Dy, Dz - incident ray direction
1202 Px, Py, Pz - intersection point
1203 Nx, Ny, Nz - surface normal at intersection point
1204 Rdot - cosine between ray and normal
1205 arg(0) - number of real arguments
1206 arg(i) - i'th real argument
1207 .DE
1208 For BRDF types, the following variables are defined as well:
1209 .DS
1210 NxP, NyP, NzP - perturbed surface normal
1211 RdotP - perturbed dot product
1212 CrP, CgP, CbP - perturbed material color
1213 .DE
1214 A unique context is set up for each file so that the same variable
1215 may appear in different function files without conflict.
1216 The variables listed above and any others defined in
1217 rayinit.cal are available globally.
1218 If no file is needed by a given primitive because all the required
1219 variables are global, a period (`.') can be given in
1220 place of the file name.
1221 It is also possible to give an expression instead of a straight
1222 variable name in a scene file, although such expressions should
1223 be kept simple as they cannot contain any white space.
1224 Also, functions (requiring parameters)
1225 must be given as names and not as expressions.
1226 .PP
1227 Constant expressions are used as an optimization in function
1228 files.
1229 They are replaced wherever they occur in an expression by their
1230 value.
1231 Constant expressions are evaluated only once, so they must not
1232 contain any variables or values that can change, such as the ray
1233 variables Px and Ny or the primitive argument function arg().
1234 All the math library functions such as sqrt() and cos() have the
1235 constant attribute, so they will be replaced by immediate values
1236 whenever they are given constant arguments.
1237 Thus, the subexpression cos(PI*sqrt(2)) is immediately replaced
1238 by its value, -.266255342, and does not cause any additional overhead
1239 in the calculation.
1240 .PP
1241 It is generally a good idea to define constants and variables before
1242 they are referred to in a function file.
1243 Although evaluation does not take place until later, the interpreter
1244 does variable scoping and constant subexpression evaluation based on
1245 what it has compiled already.
1246 For example, a variable that is defined globally in rayinit.cal then
1247 referenced in the local context of a function file cannot
1248 subsequently be redefined in the same file because the compiler
1249 has already determined the scope of the referenced variable as global.
1250 To avoid such conflicts, one can state the scope of a variable explicitly
1251 by preceding the variable name with a context mark (a back-quote) for
1252 a local variable, or following the name with a context mark for a global
1253 variable.
1254 .NH 3
1255 Data Files
1256 .PP
1257 Data files contain n-dimensional arrays of real numbers used
1258 for interpolation.
1259 Typically, definitions in a function file determine how
1260 to index and use interpolated data values.
1261 The basic data file format is as follows:
1262 .DS
1263 N
1264 beg1 end1 m1
1265 0 0 m2 x2.1 x2.2 x2.3 x2.4 .. x2.m2
1266 ...
1267 begN endN mN
1268 DATA, later dimensions changing faster.
1269 .DE
1270 N is the number of dimensions.
1271 For each dimension, the beginning and ending coordinate
1272 values and the dimension size is given.
1273 Alternatively, individual coordinate values can be given when
1274 the points are not evenly spaced.
1275 These values must either be increasing or decreasing monotonically.
1276 The data is m1*m2*...*mN real numbers in ASCII form.
1277 Comments may appear anywhere in the file, beginning with a pound
1278 sign ('#') and continuing to the end of line.
1279 .NH 3
1280 Font Files
1281 .PP
1282 A font file lists the polygons which make up a character set.
1283 Comments may appear anywhere in the file, beginning with a pound
1284 sign ('#') and continuing to the end of line.
1285 All numbers are decimal integers:
1286 .DS
1287 code n
1288 x0 y0
1289 x1 y1
1290 ...
1291 xn yn
1292 ...
1293 .DE
1294 The ASCII codes can appear in any order.
1295 N is the number of vertices, and the last is automatically
1296 connected to the first.
1297 Separate polygonal sections are joined by coincident sides.
1298 The character coordinate system is a square with lower left corner at
1299 (0,0), lower right at (255,0) and upper right at (255,255).
1300 .NH 2
1301 Generators
1302 .PP
1303 A generator is any program that produces a scene description
1304 as its output.
1305 They usually appear as commands in a scene description file.
1306 An example of a simple generator is
1307 .I genbox.
1308 .I Genbox
1309 takes the arguments of width, height and depth to produce
1310 a parallelepiped description.
1311 .I Genprism
1312 takes a list of 2-dimensional coordinates and extrudes them along a vector to
1313 produce a 3-dimensional prism.
1314 .I Genrev
1315 is a more sophisticated generator
1316 that produces an object of rotation from parametric functions
1317 for radius and axis position.
1318 .I Gensurf
1319 tessellates a surface defined by the
1320 parametric functions x(s,t), y(s,t), and z(s,t).
1321 .I Genworm
1322 links cylinders and spheres along a curve.
1323 .I Gensky
1324 produces a sun and sky distribution corresponding
1325 to a given time and date.
1326 .PP
1327 .I Xform
1328 is a program that transforms a scene description from one
1329 coordinate space to another.
1330 .I Xform
1331 does rotation, translation, scaling, and mirroring.
1332 .NH 1
1333 Image Generation
1334 .PP
1335 Once the scene has been described in three-dimensions, it
1336 is possible to generate a two-dimensional image from a
1337 given perspective.
1338 .PP
1339 The image generating programs use an
1340 .I octree
1341 to efficiently trace rays through the scene.
1342 An octree subdivides space into nested octants which
1343 contain sets of surfaces.
1344 In RADIANCE, an octree is created from a scene description by
1345 .I oconv.
1346 The details of this process are not important,
1347 but the octree will serve as input to the ray-tracing
1348 programs and directs the use of a scene description.
1349 .PP
1350 .I Rview
1351 is ray-tracing program for viewing a scene interactively.
1352 When the user specifies a new perspective,
1353 .I rview
1354 quickly displays a rough
1355 image on the terminal, then progressively
1356 increases the resolution as the user looks on.
1357 He can select a particular section of the image to improve,
1358 or move to a different view and start over.
1359 This mode of interaction is useful for debugging scenes
1360 as well as determining the best view for a final image.
1361 .PP
1362 .I Rpict
1363 produces a high-resolution picture of a scene from
1364 a particular perspective.
1365 This program features adaptive sampling, crash
1366 recovery and progress reporting, all of which are important
1367 for time-consuming images.
1368 .PP
1369 A number of filters are available for manipulating picture files.
1370 .I Pfilt
1371 sets the exposure and performs anti-aliasing.
1372 .I Pcompos
1373 composites (cuts and pastes) pictures.
1374 .I Pcond
1375 conditions a picture for a specific display device.
1376 .I Pcomb
1377 performs arbitrary math on one or more pictures.
1378 .I Protate
1379 rotates a picture 90 degrees clockwise.
1380 .I Pflip
1381 flips a picture horizontally, vertically, or both (180 degree rotation).
1382 .I Pvalue
1383 converts a picture to and from simpler formats.
1384 .PP
1385 Pictures may be displayed directly under X11 using the program
1386 .I ximage,
1387 or converted a standard image format.
1388 .I Ra_avs
1389 converts to and from AVS image format.
1390 .I Ra_pict
1391 converts to Macintosh 32-bit PICT2 format.
1392 .I Ra_ppm
1393 converts to and from Poskanzer Portable Pixmap formats.
1394 .I Ra_pr
1395 converts to and from Sun 8-bit rasterfile format.
1396 .I Ra_pr24
1397 converts to and from Sun 24-bit rasterfile format.
1398 .I Ra_ps
1399 converts to PostScript color and greyscale formats.
1400 .I Ra_rgbe
1401 converts to and from Radiance uncompressed picture format.
1402 .I Ra_t16
1403 converts to and from Targa 16 and 24-bit image formats.
1404 .I Ra_t8
1405 converts to and from Targa 8-bit image format.
1406 .I Ra_tiff
1407 converts to and from TIFF.
1408 .I Ra_xyze
1409 converts to and from Radiance CIE picture format.
1410 .NH 1
1411 License
1412 .PP
1413 Radiance is a registered copyright of The Regents of the University of
1414 California ("The Regents"). The Regents grant to you a nonexclusive,
1415 nontransferable license ("License") to use Radiance source code without fee.
1416 You may not sell or distribute Radiance to others without the prior express
1417 written permission of The Regents.
1418 You may compile and use this software on any machines to which you have
1419 personal access, and may share its use with others who have access to the
1420 same machines.
1421 .PP
1422 NEITHER THE UNITED STATES NOR THE UNITED STATES DEPARTMENT OF ENERGY, NOR ANY
1423 OF THEIR EMPLOYEES, MAKES ANY WARRANTY, EXPRESS OR IMPLIED, OR ASSUMES ANY
1424 LEGAL LIABILITY OR RESPONSIBILITY FOR THE ACCURACY, COMPLETENESS, OR
1425 USEFULNESS OF ANY INFORMATION, APPARATUS, PRODUCT, OR PROCESS DISCLOSED, OR
1426 REPRESENTS THAT ITS USE WOULD NOT INFRINGE PRIVATELY OWNED RIGHTS.
1427 By downloading, using or copying this software, you agree to abide by the
1428 intellectual property laws and all other applicable laws of the United
1429 States, and by the terms of this License Agreement. Ownership of the software
1430 shall remain solely in The Regents.
1431 The Regents shall have the right to terminate this License immediately by
1432 written notice upon your breach of, or noncompliance with, any of its terms.
1433 You shall be liable for any infringement or damages resulting from your
1434 failure to abide by the terms of this License Agreement.
1435 .PP
1436 NOTICE: The Government is granted for itself and others acting on its behalf
1437 a paid-up, nonexclusive irrevocable worldwide license in this data to
1438 reproduce, prepare derivative works, and perform publicly and display
1439 publicly. Beginning five (5) years after permission to assert copyright is
1440 granted, subject to two possible five year renewals, the Government is
1441 granted for itself and others acting on its behalf a paid-up, non-exclusive,
1442 irrevocable worldwide license in this data to reproduce, prepare derivative
1443 works, distribute copies to the public, perform publicly and display
1444 publicly, and to permit others to do so.
1445 .NH 1
1446 Acknowledgements
1447 .PP
1448 This work was supported by the Assistant Secretary of Conservation
1449 and Renewable Energy, Office of Building Energy Research and
1450 Development, Buildings Equipment Division of the U.S. Department of
1451 Energy under Contract No. DE-AC03-76SF00098.
1452 .PP
1453 Additional work was sponsored by the Swiss federal government
1454 under the Swiss LUMEN Project and was
1455 carried out in the Laboratoire d'Energie Solaire (LESO Group) at
1456 the Ecole Polytechnique Federale de Lausanne (EPFL University)
1457 in Lausanne, Switzerland.
1458 .NH 1
1459 References
1460 .LP
1461 Ward, G.,
1462 ``The Radiance Lighting Simulation and Rendering System,''
1463 .I "Computer Graphics",
1464 Orlando, July 1994.
1465 .LP
1466 Rushmeier, H., G. Ward,
1467 ``Energy-Preserving Non-Linear Filters,''
1468 .I "Computer Graphics",
1469 Orlando, July 1994.
1470 .LP
1471 Ward, G.,
1472 ``A Contrast-Based Scalefactor for Luminance Display,''
1473 .I "Graphics Gems IV",
1474 Edited by Paul Heckbert,
1475 Academic Press 1994.
1476 .LP
1477 Ward, G.,
1478 ``Measuring and Modeling Anisotropic Reflection,''
1479 .I "Computer Graphics",
1480 Chicago, July 1992.
1481 .LP
1482 Ward, G., P. Heckbert,
1483 ``Irradiance Gradients,''
1484 .I "Third Annual Eurographics Workshop on Rendering",
1485 to be published by Springer-Verlag, held in Bristol, UK, May 1992.
1486 .LP
1487 Ward, G.,
1488 ``Adaptive Shadow Testing for Ray Tracing,''
1489 .I "Second Annual Eurographics Workshop on Rendering",
1490 to be published by Springer-Verlag, held in Barcelona, SPAIN, May 1991.
1491 .LP
1492 Ward, G.,
1493 ``Visualization,''
1494 .I "Lighting Design and Application",
1495 Vol. 20, No. 6, June 1990.
1496 .LP
1497 Ward, G., F. Rubinstein, R. Clear,
1498 ``A Ray Tracing Solution for Diffuse Interreflection,''
1499 .I "Computer Graphics",
1500 Vol. 22, No. 4, August 1988.
1501 .LP
1502 Ward, G., F. Rubinstein,
1503 ``A New Technique for Computer Simulation of Illuminated Spaces,''
1504 .I "Journal of the Illuminating Engineering Society",
1505 Vol. 17, No. 1, Winter 1988.