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Revision: 1.37
Committed: Mon Oct 8 20:18:27 2018 UTC (5 years, 7 months ago) by greg
Branch: MAIN
CVS Tags: rad5R2
Changes since 1.36: +3 -3 lines
Log Message:
Preparation for 5.2 release

File Contents

# Content
1 .\" RCSid "$Id: ray.1,v 1.36 2018/10/08 20:04:09 greg Exp $"
2 .\" Print using the -ms macro package
3 .DA 10/08/2018
4 .LP
5 .tl """Copyright \(co 2018 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 Building Technologies Department
14 .br
15 Lawrence Berkeley Laboratory
16 .br
17 1 Cyclotron Rd., MS 90-3111
18 .br
19 Berkeley, CA 94720
20 .NH 1
21 Introduction
22 .PP
23 RADIANCE was developed as a research tool
24 for predicting the distribution of visible radiation in
25 illuminated spaces.
26 It takes as input a three-dimensional geometric model of
27 the physical environment, and produces a map of
28 spectral radiance values in a color image.
29 The technique of ray-tracing follows light backwards
30 from the image plane to the source(s).
31 Because it can produce realistic images from a simple description,
32 RADIANCE has a wide range of applications in graphic arts,
33 lighting design, computer-aided engineering and architecture.
34 .KF
35 .sp 25
36 .ce
37 .B "Figure 1."
38 .sp
39 .KE
40 .PP
41 The diagram in Figure 1 shows the flow between programs (boxes) and
42 data (ovals).
43 The central program is
44 .I rpict,
45 which produces a picture from a scene description.
46 .I Rview
47 is a variation of
48 .I rpict
49 that computes and displays images interactively.
50 Other programs (not shown) connect many of these elements together,
51 such as the executive programs
52 .I rad
53 and
54 .I ranimate,
55 the interactive rendering program
56 .I rholo,
57 and the animation program
58 .I ranimove.
59 The program
60 .I obj2mesh
61 acts as both a converter and scene compiler, converting a Wavefront .OBJ
62 file into a compiled mesh octree for efficient rendering.
63 .PP
64 A scene description file lists the surfaces and materials
65 that make up a specific environment.
66 The current surface types are spheres, polygons, cones, and cylinders.
67 There is also a composite surface type, called mesh, and a pseudosurface
68 type, called instance, which facilitates very complex geometries.
69 Surfaces can be made from materials such as plastic, metal, and glass.
70 Light sources can be distant disks as well as local spheres, disks
71 and polygons.
72 .PP
73 From a three-dimensional scene description and a specified view,
74 .I rpict
75 produces a two-dimensional image.
76 A picture file is a compressed binary representation of the
77 pixels in the image.
78 This picture can be scaled in size and
79 brightness, anti-aliased, and sent to a graphics output device.
80 .PP
81 A header in each picture file lists the program(s) and
82 parameters that produced it.
83 This is useful for identifying a picture
84 without having to display it.
85 The information can be read by the program
86 .I getinfo.
87 .NH 1
88 Scene Description
89 .PP
90 A scene description file represents a
91 three-dimensional physical environment
92 in Cartesian (rectilinear) world coordinates.
93 It is stored as ASCII text, with the following basic format:
94 .DS
95 # comment
97 modifier type identifier
98 n S1 S2 "S 3" .. Sn
99 0
100 m R1 R2 R3 .. Rm
102 modifier alias identifier reference
104 ! command
106 ...
107 .DE
108 .PP
109 A comment line begins with a pound sign, `#'.
110 .PP
111 The scene description
112 .I primitives
113 all have the same general format, and can
114 be either surfaces or modifiers.
115 A primitive has a modifier, a type, and an identifier.
116 A modifier is either the identifier of a
117 .I "previously defined"
118 primitive, or "void"\(dg.
119 .FS
120 \(dgThe most recent definition of a modifier is the one used,
121 and later definitions do not cause relinking of loaded
122 primitives.
123 Thus, the same identifier may be used repeatedly, and each new
124 definition will apply to the primitives following it.
125 .FE
126 An identifier can be any string (i.e., any sequence of non-white characters).
127 The
128 .I arguments
129 associated with a primitive can be strings or real numbers.
130 The first integer following the identifier is the number
131 of string arguments, and it is followed by the arguments themselves
132 (separated by white space or enclosed in quotes).
133 The next integer is the number of integer arguments, and is followed
134 by the integer arguments.
135 (There are currently no primitives that use them, however.)
136 The next integer is the real argument count, and it is followed
137 by the real arguments.
138 .PP
139 An alias gets its type and arguments from a previously defined primitive.
140 This is useful when the same material is used with a different
141 modifier, or as a convenient naming mechanism.
142 The reserved modifier name "inherit" may be used to specificy that
143 an alias will inherit its modifier from the original.
144 Surfaces cannot be aliased.
145 .PP
146 A line beginning with an exclamation point, `!',
147 is interpreted as a command.
148 It is executed by the shell, and its output is read as input to
149 the program.
150 The command must not try to read from its standard input, or
151 confusion will result.
152 A command may be continued over multiple lines using a backslash, `\\',
153 to escape the newline.
154 .PP
155 White space is generally ignored, except as a separator.
156 The exception is the newline character after a command or comment.
157 Commands, comments and primitives may appear in any combination, so long
158 as they are not intermingled.
159 .NH 2
160 Primitive Types
161 .PP
162 Primitives can be surfaces, materials, textures or patterns.
163 Modifiers can be materials, mixtures, textures or patterns.
164 Simple surfaces must have one material in their modifier list.
165 .NH 3
166 Surfaces
167 .PP
168 A scene description will consist mostly of surfaces.
169 The basic types are given below.
170 .LP
171 .UL Source
172 .PP
173 A source is not really a surface, but a solid angle.
174 It is used for specifying light sources that are very distant.
175 The direction to the center of the source and the number of degrees
176 subtended by its disk are given as follows:
177 .DS
178 mod source id
179 0
180 0
181 4 xdir ydir zdir angle
182 .DE
183 .LP
184 .UL Sphere
185 .PP
186 A sphere is given by its center and radius:
187 .DS
188 mod sphere id
189 0
190 0
191 4 xcent ycent zcent radius
192 .DE
193 .LP
194 .UL Bubble
195 .PP
196 A bubble is simply a sphere whose surface normal points inward.
197 .LP
198 .UL Polygon
199 .PP
200 A polygon is given by a list of three-dimensional vertices,
201 which are ordered counter-clockwise as viewed from
202 the front side (into the surface normal).
203 The last vertex is automatically connected to the first.
204 Holes are represented in polygons as interior vertices connected to
205 the outer perimeter by coincident edges (seams).
206 .DS
207 mod polygon id
208 0
209 0
210 3n
211 x1 y1 z1
212 x2 y2 z2
213 ...
214 xn yn zn
215 .DE
216 .LP
217 .UL Cone
218 .PP
219 A cone is a megaphone-shaped object.
220 It is truncated by two planes perpendicular to its axis,
221 and one of its ends may come to a point.
222 It is given as two axis endpoints, and the starting
223 and ending radii:
224 .DS
225 mod cone id
226 0
227 0
228 8
229 x0 y0 z0
230 x1 y1 z1
231 r0 r1
232 .DE
233 .LP
234 .UL Cup
235 .PP
236 A cup is an inverted cone (i.e., has an inward surface normal).
237 .LP
238 .UL Cylinder
239 .PP
240 A cylinder is like a cone, but its starting and ending radii are
241 equal.
242 .DS
243 mod cylinder id
244 0
245 0
246 7
247 x0 y0 z0
248 x1 y1 z1
249 rad
250 .DE
251 .LP
252 .UL Tube
253 .PP
254 A tube is an inverted cylinder.
255 .LP
256 .UL Ring
257 .PP
258 A ring is a circular disk given by its center, surface
259 normal, and inner and outer radii:
260 .DS
261 mod ring id
262 0
263 0
264 8
265 xcent ycent zcent
266 xdir ydir zdir
267 r0 r1
268 .DE
269 .LP
270 .UL Mesh
271 .PP
272 A mesh is a compound surface, made up of many triangles and
273 an octree data structure to accelerate ray intersection.
274 It is typically converted from a Wavefront .OBJ file using the
275 .I obj2mesh
276 program.
277 .DS
278 mod mesh id
279 1+ meshfile transform
280 0
281 0
282 .DE
283 If the modifier is "void", then surfaces will use the modifiers given
284 in the original mesh description.
285 Otherwise, the modifier specified is used in their place.
286 The transform moves the mesh to the desired location in the scene.
287 Multiple instances using the same meshfile take little extra memory,
288 and the compiled mesh itself takes much less space than individual
289 polygons would.
290 In the case of an unsmoothed mesh, using the mesh primitive reduces
291 memory requirements by a factor of 30 relative to individual triangles.
292 If a mesh has smoothed surfaces, we save a factor of 50 or more,
293 permitting very detailed geometries that would otherwise exhaust the
294 available memory.
295 In addition, the mesh primitive can have associated (u,v) coordinates
296 for pattern and texture mapping.
297 These are made available to function files via the Lu and Lv variables.
298 .LP
299 .UL Instance
300 .PP
301 An instance is a compound surface, given by the contents of an
302 octree file (created by oconv).
303 .DS
304 mod instance id
305 1+ octree transform
306 0
307 0
308 .DE
309 If the modifier is "void", then surfaces will use the modifiers given
310 in the original description.
311 Otherwise, the modifier specified is used in their place.
312 The transform moves the octree to the desired location in the scene.
313 Multiple instances using the same octree take little extra memory,
314 hence very complex descriptions can be rendered using this primitive.
315 .PP
316 There are a number of important limitations to be aware of when using
317 instances.
318 First, the scene description used to generate the octree must stand on
319 its own, without referring to modifiers in the parent description.
320 This is necessary for oconv to create the octree.
321 Second, light sources in the octree will not be incorporated correctly
322 in the calculation, and they are not recommended.
323 Finally, there is no advantage (other than convenience) to
324 using a single instance of an octree, or an octree containing only a
325 few surfaces.
326 An xform command on the subordinate description is prefered in such cases.
327 .NH 3
328 Materials
329 .PP
330 A material defines the way light interacts with a surface.
331 The basic types are given below.
332 .LP
333 .UL Light
334 .PP
335 Light is the basic material for self-luminous surfaces (i.e., light
336 sources).
337 In addition to the source surface type, spheres, discs (rings with zero
338 inner radius), cylinders (provided they are long enough), and
339 polygons can act as light sources.
340 Polygons work best when they are rectangular.
341 Cones cannot be used at this time.
342 A pattern may be used to specify a light output distribution.
343 Light is defined simply as a RGB radiance value (watts/steradian/m2):
344 .DS
345 mod light id
346 0
347 0
348 3 red green blue
349 .DE
350 .LP
351 .UL Illum
352 .PP
353 Illum is used for secondary light sources with broad distributions.
354 A secondary light source is treated like any other
355 light source, except when viewed directly.
356 It then acts like it is made of a different material (indicated by
357 the string argument), or becomes invisible (if no string argument is given,
358 or the argument is "void").
359 Secondary sources are useful when modeling windows or
360 brightly illuminated surfaces.
361 .DS
362 mod illum id
363 1 material
364 0
365 3 red green blue
366 .DE
367 .LP
368 .UL Glow
369 .PP
370 Glow is used for surfaces that are self-luminous, but limited
371 in their effect.
372 In addition to the radiance value, a maximum radius for
373 shadow testing is given:
374 .DS
375 mod glow id
376 0
377 0
378 4 red green blue maxrad
379 .DE
380 If maxrad is zero, then the surface will never be tested
381 for shadow, although it may participate in an interreflection calculation.
382 If maxrad is negative, then the surface will never contribute to scene
383 illumination.
384 Glow sources will never illuminate objects on the other side of an
385 illum surface.
386 This provides a convenient way to illuminate local light fixture
387 geometry without overlighting nearby objects.
388 .LP
389 .UL Spotlight
390 .PP
391 Spotlight is used for self-luminous surfaces having directed output.
392 As well as radiance, the full cone angle (in degrees)
393 and orientation (output direction) vector are given.
394 The length of the orientation vector is the distance
395 of the effective focus behind the source center (i.e., the focal length).
396 .DS
397 mod spotlight id
398 0
399 0
400 7 red green blue angle xdir ydir zdir
401 .DE
402 .LP
403 .UL Mirror
404 .PP
405 Mirror is used for planar surfaces that produce virtual
406 source reflections.
407 This material should be used sparingly, as it may cause the light
408 source calculation to blow up if it is applied to many small surfaces.
409 This material is only supported for flat surfaces such as polygons
410 and rings.
411 The arguments are simply the RGB reflectance values, which should be
412 between 0 and 1.
413 An optional string argument may be used like the illum type to specify a
414 different material to be used for shading non-source rays.
415 If this alternate material is given as "void", then the mirror surface
416 will be invisible.
417 This is only appropriate if the surface hides other (more detailed)
418 geometry with the same overall reflectance.
419 .DS
420 mod mirror id
421 1 material
422 0
423 3 red green blue
424 .DE
425 .LP
426 .UL Prism1
427 .PP
428 The prism1 material is for general light redirection from prismatic
429 glazings, generating virtual light sources.
430 It can only be used to modify a planar surface (i.e., a polygon or disk)
431 and should not result in either light concentration or scattering.
432 The new direction of the ray can be on either side of the material,
433 and the definitions must have the correct bidirectional properties
434 to work properly with virtual light sources.
435 The arguments give the coefficient for the redirected light
436 and its direction.
437 .DS
438 mod prism1 id
439 5+ coef dx dy dz funcfile transform
440 0
441 n A1 A2 .. An
442 .DE
443 The new direction variables
444 .I "dx, dy"
445 and
446 .I dz
447 need not produce a normalized vector.
448 For convenience, the variables
449 .I "DxA, DyA"
450 and
451 .I DzA
452 are defined as the normalized direction to the target light source.
453 See section 2.2.1 on function files for further information.
454 .LP
455 .UL Prism2
456 .PP
457 The material prism2 is identical to prism1 except that
458 it provides for two ray redirections rather than one.
459 .DS
460 mod prism2 id
461 9+ coef1 dx1 dy1 dz1 coef2 dx2 dy2 dz2 funcfile transform
462 0
463 n A1 A2 .. An
464 .DE
465 .LP
466 .UL Mist
467 .PP
468 Mist is a virtual material used to delineate a volume
469 of participating atmosphere.
470 A list of important light sources may be given, along with an
471 extinction coefficient, scattering albedo and scattering eccentricity
472 parameter.
473 The light sources named by the string argument list
474 will be tested for scattering within the volume.
475 Sources are identified by name, and virtual light sources may be indicated
476 by giving the relaying object followed by '>' followed by the source, i.e:
477 .DS
478 3 source1 mirror1>source10 mirror2>mirror1>source3
479 .DE
480 Normally, only one source is given per mist material, and there is an
481 upper limit of 32 to the total number of active scattering sources.
482 The extinction coefficient, if given, is added to the global
483 coefficient set on the command line.
484 Extinction is in units of 1/distance (distance based on the world coordinates),
485 and indicates the proportional loss of radiance over one unit distance.
486 The scattering albedo, if present, will override the global setting within
487 the volume.
488 An albedo of 0\00\00 means a perfectly absorbing medium, and an albedo of
489 1\01\01\0 means
490 a perfectly scattering medium (no absorption).
491 The scattering eccentricity parameter will likewise override the global
492 setting if it is present.
493 Scattering eccentricity indicates how much scattered light favors the
494 forward direction, as fit by the Henyey-Greenstein function:
495 .DS
496 P(theta) = (1 - g*g) / (1 + g*g - 2*g*cos(theta))^1.5
497 .DE
498 A perfectly isotropic scattering medium has a g parameter of 0, and
499 a highly directional material has a g parameter close to 1.
500 Fits to the g parameter may be found along with typical extinction
501 coefficients and scattering albedos for various atmospheres and
502 cloud types in USGS meteorological tables.
503 (A pattern will be applied to the extinction values.)\0
504 .DS
505 mod mist id
506 N src1 src2 .. srcN
507 0
508 0|3|6|7 [ rext gext bext [ ralb galb balb [ g ] ] ]
509 .DE
510 There are two usual uses of the mist type.
511 One is to surround a beam from a spotlight or laser so that it is
512 visible during rendering.
513 For this application, it is important to use a cone (or cylinder) that
514 is long enough and wide enough to contain the important visible portion.
515 Light source photometry and intervening objects will have the desired
516 effect, and crossing beams will result in additive scattering.
517 For this application, it is best to leave off the real arguments, and
518 use the global rendering parameters to control the atmosphere.
519 The second application is to model clouds or other localized media.
520 Complex boundary geometry may be used to give shape to a uniform medium,
521 so long as the boundary encloses a proper volume.
522 Alternatively, a pattern may be used to set the line integral value
523 through the cloud for a ray entering or exiting a point in a given
524 direction.
525 For this application, it is best if cloud volumes do not overlap each other,
526 and opaque objects contained within them may not be illuminated correctly
527 unless the line integrals consider enclosed geometry.
528 .LP
529 .UL Plastic
530 .PP
531 Plastic is a material with uncolored highlights.
532 It is given by its RGB reflectance, its fraction of specularity,
533 and its roughness value.
534 Roughness is specified as the rms slope of surface facets.
535 A value of 0 corresponds to a perfectly smooth surface, and
536 a value of 1 would be a very rough surface.
537 Specularity fractions greater than 0.1 and
538 roughness values greater than 0.2 are not very
539 realistic.
540 (A pattern modifying plastic will affect the material color.)
541 .DS
542 mod plastic id
543 0
544 0
545 5 red green blue spec rough
546 .DE
547 .LP
548 .UL Metal
549 .PP
550 Metal is similar to plastic, but specular highlights
551 are modified by the material color.
552 Specularity of metals is usually .9 or greater.
553 As for plastic, roughness values above .2 are uncommon.
554 .LP
555 .UL Trans
556 .PP
557 Trans is a translucent material, similar to plastic.
558 The transmissivity is the fraction of penetrating light that
559 travels all the way through the material.
560 The transmitted specular component is the fraction of transmitted
561 light that is not diffusely scattered.
562 Transmitted and diffusely reflected light is modified by the material color.
563 Translucent objects are infinitely thin.
564 .DS
565 mod trans id
566 0
567 0
568 7 red green blue spec rough trans tspec
569 .DE
570 .LP
571 .UL Plastic2
572 .PP
573 Plastic2 is similar to plastic, but with anisotropic
574 roughness.
575 This means that highlights in the surface will appear elliptical rather
576 than round.
577 The orientation of the anisotropy is determined by the unnormalized
578 direction vector
579 .I "ux uy uz".
580 These three expressions (separated by white space) are evaluated in
581 the context of the function file
582 .I funcfile.
583 If no function file is required (i.e., no special variables or
584 functions are required), a period (`.') may be given in its
585 place.
586 (See the discussion of Function Files in the Auxiliary Files section).
587 The
588 .I urough
589 value defines the roughness along the
590 .B u
591 vector given projected onto the surface.
592 The
593 .I vrough
594 value defines the roughness perpendicular to this vector.
595 Note that the highlight will be narrower in the direction of the
596 smaller roughness value.
597 Roughness values of zero are not allowed for efficiency reasons
598 since the behavior would be the same as regular plastic in that
599 case.
600 .DS
601 mod plastic2 id
602 4+ ux uy uz funcfile transform
603 0
604 6 red green blue spec urough vrough
605 .DE
606 .LP
607 .UL Metal2
608 .PP
609 Metal2 is the same as plastic2, except that the highlights are
610 modified by the material color.
611 .LP
612 .UL Trans2
613 .PP
614 Trans2 is the anisotropic version of trans.
615 The string arguments are the same as for plastic2, and the real
616 arguments are the same as for trans but with an additional roughness
617 value.
618 .DS
619 mod trans2 id
620 4+ ux uy uz funcfile transform
621 0
622 8 red green blue spec urough vrough trans tspec
623 .DE
624 .LP
625 .UL Ashik2
626 .PP
627 Ashik2 is the anisotropic reflectance model by Ashikhmin & Shirley.
628 The string arguments are the same as for plastic2, but the real
629 arguments have additional flexibility to specify the specular color.
630 Also, rather than roughness, specular power is used, which has no
631 physical meaning other than larger numbers are equivalent to a smoother
632 surface.
633 .DS
634 mod ashik2 id
635 4+ ux uy uz funcfile transform
636 0
637 8 dred dgrn dblu sred sgrn sblu u-power v-power
638 .DE
639 .LP
640 .UL Dielectric
641 .PP
642 A dielectric material is transparent, and it refracts light
643 as well as reflecting it.
644 Its behavior is determined by the index of refraction and
645 transmission coefficient in each wavelength band per unit length.
646 Common glass has a index of refraction (n) around 1.5,
647 and a transmission coefficient of roughly 0.92 over an inch.
648 An additional number, the Hartmann constant, describes how
649 the index of refraction changes as a function of wavelength.
650 It is usually zero.
651 (A pattern modifies only the refracted value.)
652 .DS
653 mod dielectric id
654 0
655 0
656 5 rtn gtn btn n hc
657 .DE
658 .LP
659 .UL Interface
660 .PP
661 An interface is a boundary between two dielectrics.
662 The first transmission coefficient and refractive index are for the inside;
663 the second ones are for the outside.
664 Ordinary dielectrics are surrounded by a vacuum (1 1 1 1).
665 .DS
666 mod interface id
667 0
668 0
669 8 rtn1 gtn1 btn1 n1 rtn2 gtn2 btn2 n2
670 .DE
671 .LP
672 .UL Glass
673 .PP
674 Glass is similar to dielectric, but it is optimized for thin glass
675 surfaces (n = 1.52).
676 One transmitted ray and one reflected ray is produced.
677 By using a single surface is in place of two, internal reflections
678 are avoided.
679 The surface orientation is irrelevant, as it is for plastic,
680 metal, and trans.
681 The only specification required is the transmissivity at normal
682 incidence.
683 (Transmissivity is the amount of light not absorbed in one traversal
684 of the material.
685 Transmittance -- the value usually measured -- is the total light
686 transmitted through the pane including multiple reflections.)\0
687 To compute transmissivity (tn) from transmittance (Tn) use:
688 .DS
689 tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn
690 .DE
691 Standard 88% transmittance glass has a transmissivity of 0.96.
692 (A pattern modifying glass will affect the transmissivity.)
693 If a fourth real argument is given, it is interpreted as the index of
694 refraction to use instead of 1.52.
695 .DS
696 mod glass id
697 0
698 0
699 3 rtn gtn btn
700 .DE
701 .LP
702 .UL Plasfunc
703 .PP
704 Plasfunc in used for the procedural definition of plastic-like
705 materials with arbitrary bidirectional reflectance distribution
706 functions (BRDF's).
707 The arguments to this material include the color and specularity,
708 as well as the function defining the specular distribution and the
709 auxiliary file where it may be found.
710 .DS
711 mod plasfunc id
712 2+ refl funcfile transform
713 0
714 4+ red green blue spec A5 ..
715 .DE
716 The function
717 .I refl
718 takes four arguments, the x, y and z
719 direction towards the incident light, and the solid angle
720 subtended by the source.
721 The solid angle is provided to facilitate averaging, and is usually
722 ignored.
723 The
724 .I refl
725 function should integrate to 1 over
726 the projected hemisphere to maintain energy balance.
727 At least four real arguments must be given, and these are made
728 available along with any additional values to the reflectance
729 function.
730 Currently, only the contribution from direct light sources is
731 considered in the specular calculation.
732 As in most material types, the surface normal is always
733 altered to face the incoming ray.
734 .LP
735 .UL Metfunc
736 .PP
737 Metfunc is identical to plasfunc and takes the same arguments, but
738 the specular component is multiplied also by the material color.
739 .LP
740 .UL Transfunc
741 .PP
742 Transfunc is similar to plasfunc but with an arbitrary bidirectional
743 transmittance distribution as well as a reflectance distribution.
744 Both reflectance and transmittance are specified with the same function.
745 .DS
746 mod transfunc id
747 2+ brtd funcfile transform
748 0
749 6+ red green blue rspec trans tspec A7 ..
750 .DE
751 Where
752 .I trans
753 is the total light transmitted and
754 .I tspec
755 is the non-Lambertian fraction of transmitted light.
756 The function
757 .I brtd
758 should integrate to 1 over each projected hemisphere.
759 .LP
760 .UL BRTDfunc
761 .PP
762 The material BRTDfunc gives the maximum flexibility over surface
763 reflectance and transmittance, providing for spectrally-dependent
764 specular rays and reflectance and transmittance distribution functions.
765 .DS
766 mod BRTDfunc id
767 10+ rrefl grefl brefl
768 rtrns gtrns btrns
769 rbrtd gbrtd bbrtd
770 funcfile transform
771 0
772 9+ rfdif gfdif bfdif
773 rbdif gbdif bbdif
774 rtdif gtdif btdif
775 A10 ..
776 .DE
777 The variables
778 .I "rrefl, grefl"
779 and
780 .I brefl
781 specify the color coefficients for
782 the ideal specular (mirror) reflection of the surface.
783 The variables
784 .I "rtrns, gtrns"
785 and
786 .I btrns
787 specify the color coefficients for the ideal specular transmission.
788 The functions
789 .I "rbrtd, gbrtd"
790 and
791 .I bbrtd
792 take the direction to the incident light (and its solid angle)
793 and compute the color coefficients for the directional diffuse part of
794 reflection and transmission.
795 As a special case, three identical values of '0' may be given in place of
796 these function names to indicate no directional diffuse component.
797 .PP
798 Unlike most other material types, the surface normal is not altered to
799 face the incoming ray.
800 Thus, functions and variables must pay attention to the orientation of
801 the surface and make adjustments appropriately.
802 However, the special variables for the perturbed dot product and surface
803 normal,
804 .I "RdotP, NxP, NyP"
805 and
806 .I NzP
807 are reoriented as if the ray hit the front surface for convenience.
808 .PP
809 A diffuse reflection component may be given for the front side with
810 .I "rfdif, gfdif"
811 and
812 .I bfdif
813 for the front side of the surface or
814 .I "rbdif, gbdif"
815 and
816 .I bbdif
817 for the back side.
818 The diffuse transmittance (must be the same for both sides by physical law)
819 is given by
820 .I "rtdif, gtdif"
821 and
822 .I btdif.
823 A pattern will modify these diffuse scattering values,
824 and will be available through the special variables
825 .I "CrP, CgP"
826 and
827 .I CbP.
828 .PP
829 Care must be taken when using this material type to produce a physically
830 valid reflection model.
831 The reflectance functions should be bidirectional, and under no circumstances
832 should the sum of reflected diffuse, transmitted diffuse, reflected specular,
833 transmitted specular and the integrated directional diffuse component be
834 greater than one.
835 .LP
836 .UL Plasdata
837 .PP
838 Plasdata is used for arbitrary BRDF's that are most conveniently
839 given as interpolated data.
840 The arguments to this material are the data file and coordinate index
841 functions, as well as a function to optionally modify the data
842 values.
843 .DS
844 mod plasdata id
845 3+n+
846 func datafile
847 funcfile x1 x2 .. xn transform
848 0
849 4+ red green blue spec A5 ..
850 .DE
851 The coordinate indices
852 .I "(x1, x2,"
853 etc.) are themselves functions of
854 the x, y and z direction to the incident light, plus the solid angle
855 subtended by the light source (usually ignored).
856 The data function
857 .I (func)
858 takes five variables, the
859 interpolated value from the n-dimensional data file, followed by the
860 x, y and z direction to the incident light and the solid angle of the source.
861 The light source direction and size may of course be ignored by the function.
862 .LP
863 .UL Metdata
864 .PP
865 As metfunc is to plasfunc, metdata is to plasdata.
866 Metdata takes the same arguments as plasdata, but the specular
867 component is modified by the given material color.
868 .LP
869 .UL Transdata
870 .PP
871 Transdata is like plasdata but the specification includes transmittance
872 as well as reflectance.
873 The parameters are as follows.
874 .DS
875 mod transdata id
876 3+n+
877 func datafile
878 funcfile x1 x2 .. xn transform
879 0
880 6+ red green blue rspec trans tspec A7 ..
881 .DE
882 .LP
883 .UL BSDF
884 .PP
885 The BSDF material type loads an XML (eXtensible Markup Language)
886 file describing a bidirectional scattering distribution function.
887 Real arguments to this material may define additional
888 diffuse components that augment the BSDF data.
889 String arguments are used to define thickness for proxied
890 surfaces and the "up" orientation for the material.
891 .DS
892 mod BSDF id
893 6+ thick BSDFfile ux uy uz funcfile transform
894 0
895 0|3|6|9
896 rfdif gfdif bfdif
897 rbdif gbdif bbdif
898 rtdif gtdif btdif
899 .DE
900 The first string argument is a "thickness" parameter that may be used
901 to hide detail geometry being proxied by an aggregate BSDF material.
902 If a view or shadow ray hits a BSDF proxy with non-zero thickness,
903 it will pass directly through as if the surface were not there.
904 Similar to the illum type, this permits direct viewing and
905 shadow testing of complex geometry.
906 The BSDF is used when a scattered (indirect) ray hits the surface,
907 and any transmitted sample rays will be offset by the thickness amount
908 to avoid the hidden geometry and gather samples from the other side.
909 In this manner, BSDF surfaces can improve the results for indirect
910 scattering from complex systems without sacrificing appearance or
911 shadow accuracy.
912 If the BSDF has transmission and back-side reflection data,
913 a parallel BSDF surface may be
914 placed slightly less than the given thickness away from the front surface
915 to enclose the complex geometry on both sides.
916 The sign of the thickness is important, as it indicates whether the
917 proxied geometry is behind the BSDF surface (when thickness is positive)
918 or in front (when thickness is negative).
919 .LP
920 The second string argument is the name of the BSDF file, which is
921 found in the usual auxiliary locations.
922 The following three string parameters name variables for an "up" vector,
923 which together with the surface normal, define the
924 local coordinate system that orients the BSDF.
925 These variables, along with the thickness, are defined in a function
926 file given as the next string argument.
927 An optional transform is used to scale the thickness and reorient the up vector.
928 .LP
929 If no real arguments are given, the BSDF is used by itself to determine
930 reflection and transmission.
931 If there are at least 3 real arguments, the first triplet is an
932 additional diffuse reflectance for the front side.
933 At least 6 real arguments adds diffuse reflectance to the rear side of the surface.
934 If there are 9 real arguments, the final triplet will be taken as an additional
935 diffuse transmittance.
936 All diffuse components as well as the non-diffuse transmission are
937 modified by patterns applied to this material.
938 The non-diffuse reflection from either side are unaffected.
939 Textures perturb the effective surface normal in the usual way.
940 .LP
941 The surface normal of this type is not altered to face the incoming ray,
942 so the front and back BSDF reflections may differ.
943 (Transmission is identical front-to-back by physical law.)\0
944 If back visibility is turned off during rendering and there is no
945 transmission or back-side reflection, only then the surface will be
946 invisible from behind.
947 Unlike other data-driven material types, the BSDF type is fully
948 supported and all parts of the distribution are properly sampled.
949 .LP
950 .UL aBSDF
951 .PP
952 The aBSDF material is identical to the BSDF type with two important
953 differences.
954 First, proxy geometry is not supported, so there is no thickness parameter.
955 Second, an aBSDF is assumed to have some specular through component
956 (the 'a' stands for "aperture"), which
957 is treated specially during the direct calculation and when viewing the
958 material.
959 Based on the BSDF data, the coefficient of specular transmission is
960 determined and used for modifying unscattered shadow and view rays.
961 .DS
962 mod aBSDF id
963 5+ BSDFfile ux uy uz funcfile transform
964 0
965 0|3|6|9
966 rfdif gfdif bfdif
967 rbdif gbdif bbdif
968 rtdif gtdif btdif
969 .DE
970 .LP
971 If a material has no specular transmitted component, it is much better
972 to use the BSDF type with a zero thickness than to use aBSDF.
973 .LP
974 .UL Antimatter
975 .PP
976 Antimatter is a material that can "subtract" volumes from other volumes.
977 A ray passing into an antimatter object becomes blind to all the specified
978 modifiers:
979 .DS
980 mod antimatter id
981 N mod1 mod2 .. modN
982 0
983 0
984 .DE
985 The first modifier will also be used to shade the area leaving the
986 antimatter volume and entering the regular volume.
987 If mod1 is void, the antimatter volume is completely invisible.
988 If shading is desired at antimatter surfaces, it is important
989 that the related volumes are closed with outward-facing normals.
990 Antimatter surfaces should not intersect with other antimatter boundaries,
991 and it is unwise to use the same modifier in nested antimatter volumes.
992 The viewpoint must be outside all volumes concerned for a correct
993 rendering.
994 .NH 3
995 Textures
996 .PP
997 A texture is a perturbation of the surface normal, and
998 is given by either a function or data.
999 .LP
1000 .UL Texfunc
1001 .PP
1002 A texfunc uses an auxiliary function file
1003 to specify a procedural texture:
1004 .DS
1005 mod texfunc id
1006 4+ xpert ypert zpert funcfile transform
1007 0
1008 n A1 A2 .. An
1009 .DE
1010 .LP
1011 .UL Texdata
1012 .PP
1013 A texdata texture uses three data files to get the surface
1014 normal perturbations.
1015 The variables
1016 .I xfunc,
1017 .I yfunc
1018 and
1019 .I zfunc
1020 take three arguments
1021 each from the interpolated values in
1022 .I xdfname,
1023 .I ydfname
1024 and
1025 .I zdfname.
1026 .DS
1027 mod texdata id
1028 8+ xfunc yfunc zfunc xdfname ydfname zdfname vfname x0 x1 .. xf
1029 0
1030 n A1 A2 .. An
1031 .DE
1032 .NH 3
1033 Patterns
1034 .PP
1035 Patterns are used to modify the reflectance of materials.
1036 The basic types are given below.
1037 .LP
1038 .UL Colorfunc
1039 .PP
1040 A colorfunc is a procedurally defined color pattern.
1041 It is specified as follows:
1042 .DS
1043 mod colorfunc id
1044 4+ red green blue funcfile transform
1045 0
1046 n A1 A2 .. An
1047 .DE
1048 .LP
1049 .UL Brightfunc
1050 .PP
1051 A brightfunc is the same as a colorfunc, except it is monochromatic.
1052 .DS
1053 mod brightfunc id
1054 2+ refl funcfile transform
1055 0
1056 n A1 A2 .. An
1057 .DE
1058 .LP
1059 .UL Colordata
1060 .PP
1061 Colordata uses an interpolated data map to modify a material's color.
1062 The map is n-dimensional, and is stored in three
1063 auxiliary files, one for each color.
1064 The coordinates used to look up and interpolate the data are
1065 defined in another auxiliary file.
1066 The interpolated data values are modified by functions of
1067 one or three variables.
1068 If the functions are of one variable, then they are passed the
1069 corresponding color component (red or green or blue).
1070 If the functions are of three variables, then they are passed the
1071 original red, green, and blue values as parameters.
1072 .DS
1073 mod colordata id
1074 7+n+
1075 rfunc gfunc bfunc rdatafile gdatafile bdatafile
1076 funcfile x1 x2 .. xn transform
1077 0
1078 m A1 A2 .. Am
1079 .DE
1080 .LP
1081 .UL Brightdata
1082 .PP
1083 Brightdata is like colordata, except monochromatic.
1084 .DS
1085 mod brightdata id
1086 3+n+
1087 func datafile
1088 funcfile x1 x2 .. xn transform
1089 0
1090 m A1 A2 .. Am
1091 .DE
1092 .LP
1093 .UL Colorpict
1094 .PP
1095 Colorpict is a special case of colordata, where the pattern is
1096 a two-dimensional image stored in the RADIANCE picture format.
1097 The dimensions of the image data are determined by the picture
1098 such that the smaller dimension is always 1, and the other
1099 is the ratio between the larger and the smaller.
1100 For example, a 500x338 picture would have coordinates (u,v)
1101 in the rectangle between (0,0) and (1.48,1).
1102 .DS
1103 mod colorpict id
1104 7+
1105 rfunc gfunc bfunc pictfile
1106 funcfile u v transform
1107 0
1108 m A1 A2 .. Am
1109 .DE
1110 .LP
1111 .UL Colortext
1112 .PP
1113 Colortext is dichromatic writing in a polygonal font.
1114 The font is defined in an auxiliary file, such as
1115 .I helvet.fnt.
1116 The text itself is also specified in a separate file, or
1117 can be part of the material arguments.
1118 The character size, orientation, aspect ratio and slant is
1119 determined by right and down motion vectors.
1120 The upper left origin for the text block as well as
1121 the foreground and background colors
1122 must also be given.
1123 .DS
1124 mod colortext id
1125 2 fontfile textfile
1126 0
1127 15+
1128 Ox Oy Oz
1129 Rx Ry Rz
1130 Dx Dy Dz
1131 rfore gfore bfore
1132 rback gback bback
1133 [spacing]
1134 .DE
1135 or:
1136 .DS
1137 mod colortext id
1138 2+N fontfile . This is a line with N words ...
1139 0
1140 15+
1141 Ox Oy Oz
1142 Rx Ry Rz
1143 Dx Dy Dz
1144 rfore gfore bfore
1145 rback gback bback
1146 [spacing]
1147 .DE
1148 .LP
1149 .UL Brighttext
1150 .PP
1151 Brighttext is like colortext, but the writing is monochromatic.
1152 .DS
1153 mod brighttext id
1154 2 fontfile textfile
1155 0
1156 11+
1157 Ox Oy Oz
1158 Rx Ry Rz
1159 Dx Dy Dz
1160 foreground background
1161 [spacing]
1162 .DE
1163 or:
1164 .DS
1165 mod brighttext id
1166 2+N fontfile . This is a line with N words ...
1167 0
1168 11+
1169 Ox Oy Oz
1170 Rx Ry Rz
1171 Dx Dy Dz
1172 foreground background
1173 [spacing]
1174 .DE
1175 .LP
1176 By default, a uniform spacing algorithm is used that guarantees
1177 every character will appear in a precisely determined position.
1178 Unfortunately, such a scheme results in rather unattractive and difficult to
1179 read text with most fonts.
1180 The optional
1181 .I spacing
1182 value defines the distance between characters for proportional spacing.
1183 A positive value selects a spacing algorithm that preserves right margins and
1184 indentation, but does not provide the ultimate in proportionally spaced text.
1185 A negative value insures that characters are properly spaced, but the
1186 placement of words then varies unpredictably.
1187 The choice depends on the relative importance of spacing versus formatting.
1188 When presenting a section of formatted text, a positive spacing value is
1189 usually preferred.
1190 A single line of text will often be accompanied by a negative spacing value.
1191 A section of text meant to depict a picture, perhaps using a special purpose
1192 font such as hexbit4x1.fnt, calls for uniform spacing.
1193 Reasonable magnitudes for proportional spacing are
1194 between 0.1 (for tightly spaced characters) and 0.3 (for wide spacing).
1195 .NH 3
1196 Mixtures
1197 .PP
1198 A mixture is a blend of one or more materials or textures and patterns.
1199 Blended materials should not be light source types or virtual source types.
1200 The basic types are given below.
1201 .LP
1202 .UL Mixfunc
1203 .PP
1204 A mixfunc mixes two modifiers procedurally.
1205 It is specified as follows:
1206 .DS
1207 mod mixfunc id
1208 4+ foreground background vname funcfile transform
1209 0
1210 n A1 A2 .. An
1211 .DE
1212 Foreground and background are modifier names that must be
1213 defined earlier in the scene description.
1214 If one of these is a material, then
1215 the modifier of the mixfunc must be "void".
1216 (Either the foreground or background modifier may be "void",
1217 which serves as a form of opacity control when used with a material.)\0
1218 Vname is the coefficient defined in funcfile that determines the influence
1219 of foreground.
1220 The background coefficient is always (1-vname).
1221 .LP
1222 .UL Mixdata
1223 .PP
1224 Mixdata combines two modifiers using an auxiliary data file:
1225 .DS
1226 mod mixdata id
1227 5+n+
1228 foreground background func datafile
1229 funcfile x1 x2 .. xn transform
1230 0
1231 m A1 A2 .. Am
1232 .DE
1233 .LP
1234 .UL Mixpict
1235 .PP
1236 Mixpict combines two modifiers based on a picture:
1237 .DS
1238 mod mixpict id
1239 7+
1240 foreground background func pictfile
1241 funcfile u v transform
1242 0
1243 m A1 A2 .. Am
1244 .DE
1245 The mixing coefficient function "func" takes three
1246 arguments, the red, green and blue values
1247 corresponding to the pixel at (u,v).
1248 .LP
1249 .UL Mixtext
1250 .PP
1251 Mixtext uses one modifier for the text foreground, and one for the
1252 background:
1253 .DS
1254 mod mixtext id
1255 4 foreground background fontfile textfile
1256 0
1257 9+
1258 Ox Oy Oz
1259 Rx Ry Rz
1260 Dx Dy Dz
1261 [spacing]
1262 .DE
1263 or:
1264 .DS
1265 mod mixtext id
1266 4+N
1267 foreground background fontfile .
1268 This is a line with N words ...
1269 0
1270 9+
1271 Ox Oy Oz
1272 Rx Ry Rz
1273 Dx Dy Dz
1274 [spacing]
1275 .DE
1276 .NH 2
1277 Auxiliary Files
1278 .PP
1279 Auxiliary files used in textures and patterns
1280 are accessed by the programs during image generation.
1281 These files may be located in the working directory, or in
1282 a library directory.
1283 The environment variable
1285 can be assigned an alternate set of search directories.
1286 Following is a brief description of some common file types.
1287 .NH 3
1288 Function Files
1289 .PP
1290 A function file contains the definitions of variables, functions
1291 and constants used by a primitive.
1292 The transformation that accompanies the file name contains the necessary
1293 rotations, translations and scalings to bring the coordinates of
1294 the function file into agreement with the world coordinates.
1295 The transformation specification is the same as for the
1296 .I xform
1297 command.
1298 An example function file is given below:
1299 .DS
1300 {
1301 This is a comment, enclosed in curly braces.
1302 {Comments can be nested.}
1303 }
1304 { standard expressions use +,-,*,/,^,(,) }
1305 vname = Ny * func(A1) ;
1306 { constants are defined with a colon }
1307 const : sqrt(PI/2) ;
1308 { user-defined functions add to library }
1309 func(x) = 5 + A1*sin(x/3) ;
1310 { functions may be passed and recursive }
1311 rfunc(f,x) = if(x,f(x),f(-x)*rfunc(f,x+1)) ;
1312 { constant functions may also be defined }
1313 cfunc(x) : 10*x / sqrt(x) ;
1314 .DE
1315 Many variables and functions are already defined by the program,
1316 and they are listed in the file
1317 .I
1318 The following variables are particularly important:
1319 .DS
1320 Dx, Dy, Dz - incident ray direction
1321 Nx, Ny, Nz - surface normal at intersection point
1322 Px, Py, Pz - intersection point
1323 T - distance from start
1324 Ts - single ray (shadow) distance
1325 Rdot - cosine between ray and normal
1326 arg(0) - number of real arguments
1327 arg(i) - i'th real argument
1328 .DE
1329 For mesh objects, the local surface coordinates are available:
1330 .DS
1331 Lu, Lv - local (u,v) coordinates
1332 .DE
1333 For BRDF types, the following variables are defined as well:
1334 .DS
1335 NxP, NyP, NzP - perturbed surface normal
1336 RdotP - perturbed dot product
1337 CrP, CgP, CbP - perturbed material color
1338 .DE
1339 A unique context is set up for each file so that the same variable
1340 may appear in different function files without conflict.
1341 The variables listed above and any others defined in
1342 are available globally.
1343 If no file is needed by a given primitive because all the required
1344 variables are global, a period (`.') can be given in
1345 place of the file name.
1346 It is also possible to give an expression instead of a straight
1347 variable name in a scene file.
1348 Functions (requiring parameters)
1349 must be given as names and not as expressions.
1350 .PP
1351 Constant expressions are used as an optimization in function
1352 files.
1353 They are replaced wherever they occur in an expression by their
1354 value.
1355 Constant expressions are evaluated only once, so they must not
1356 contain any variables or values that can change, such as the ray
1357 variables Px and Ny or the primitive argument function arg().
1358 All the math library functions such as sqrt() and cos() have the
1359 constant attribute, so they will be replaced by immediate values
1360 whenever they are given constant arguments.
1361 Thus, the subexpression cos(PI*sqrt(2)) is immediately replaced
1362 by its value, -.266255342, and does not cause any additional overhead
1363 in the calculation.
1364 .PP
1365 It is generally a good idea to define constants and variables before
1366 they are referred to in a function file.
1367 Although evaluation does not take place until later, the interpreter
1368 does variable scoping and constant subexpression evaluation based on
1369 what it has compiled already.
1370 For example, a variable that is defined globally in then
1371 referenced in the local context of a function file cannot
1372 subsequently be redefined in the same file because the compiler
1373 has already determined the scope of the referenced variable as global.
1374 To avoid such conflicts, one can state the scope of a variable explicitly
1375 by preceding the variable name with a context mark (a back-quote) for
1376 a local variable, or following the name with a context mark for a global
1377 variable.
1378 .NH 3
1379 Data Files
1380 .PP
1381 Data files contain n-dimensional arrays of real numbers used
1382 for interpolation.
1383 Typically, definitions in a function file determine how
1384 to index and use interpolated data values.
1385 The basic data file format is as follows:
1386 .DS
1387 N
1388 beg1 end1 m1
1389 0 0 m2 x2.1 x2.2 x2.3 x2.4 .. x2.m2
1390 ...
1391 begN endN mN
1392 DATA, later dimensions changing faster.
1393 .DE
1394 N is the number of dimensions.
1395 For each dimension, the beginning and ending coordinate
1396 values and the dimension size is given.
1397 Alternatively, individual coordinate values can be given when
1398 the points are not evenly spaced.
1399 These values must either be increasing or decreasing monotonically.
1400 The data is m1*m2*...*mN real numbers in ASCII form.
1401 Comments may appear anywhere in the file, beginning with a pound
1402 sign ('#') and continuing to the end of line.
1403 .NH 3
1404 Font Files
1405 .PP
1406 A font file lists the polygons which make up a character set.
1407 Comments may appear anywhere in the file, beginning with a pound
1408 sign ('#') and continuing to the end of line.
1409 All numbers are decimal integers:
1410 .DS
1411 code n
1412 x0 y0
1413 x1 y1
1414 ...
1415 xn yn
1416 ...
1417 .DE
1418 The ASCII codes can appear in any order.
1419 N is the number of vertices, and the last is automatically
1420 connected to the first.
1421 Separate polygonal sections are joined by coincident sides.
1422 The character coordinate system is a square with lower left corner at
1423 (0,0), lower right at (255,0) and upper right at (255,255).
1424 .NH 2
1425 Generators
1426 .PP
1427 A generator is any program that produces a scene description
1428 as its output.
1429 They usually appear as commands in a scene description file.
1430 An example of a simple generator is
1431 .I genbox.
1432 .I Genbox
1433 takes the arguments of width, height and depth to produce
1434 a parallelepiped description.
1435 .I Genprism
1436 takes a list of 2-dimensional coordinates and extrudes them along a vector to
1437 produce a 3-dimensional prism.
1438 .I Genrev
1439 is a more sophisticated generator
1440 that produces an object of rotation from parametric functions
1441 for radius and axis position.
1442 .I Gensurf
1443 tessellates a surface defined by the
1444 parametric functions x(s,t), y(s,t), and z(s,t).
1445 .I Genworm
1446 links cylinders and spheres along a curve.
1447 .I Gensky
1448 produces a sun and sky distribution corresponding
1449 to a given time and date.
1450 .PP
1451 .I Xform
1452 is a program that transforms a scene description from one
1453 coordinate space to another.
1454 .I Xform
1455 does rotation, translation, scaling, and mirroring.
1456 .NH 1
1457 Image Generation
1458 .PP
1459 Once the scene has been described in three-dimensions, it
1460 is possible to generate a two-dimensional image from a
1461 given perspective.
1462 .PP
1463 The image generating programs use an
1464 .I octree
1465 to efficiently trace rays through the scene.
1466 An octree subdivides space into nested octants which
1467 contain sets of surfaces.
1468 In RADIANCE, an octree is created from a scene description by
1469 .I oconv.
1470 The details of this process are not important,
1471 but the octree will serve as input to the ray-tracing
1472 programs and directs the use of a scene description.
1473 .PP
1474 .I Rview
1475 is ray-tracing program for viewing a scene interactively.
1476 When the user specifies a new perspective,
1477 .I rview
1478 quickly displays a rough
1479 image on the terminal, then progressively
1480 increases the resolution as the user looks on.
1481 He can select a particular section of the image to improve,
1482 or move to a different view and start over.
1483 This mode of interaction is useful for debugging scenes
1484 as well as determining the best view for a final image.
1485 .PP
1486 .I Rpict
1487 produces a high-resolution picture of a scene from
1488 a particular perspective.
1489 This program features adaptive sampling, crash
1490 recovery and progress reporting, all of which are important
1491 for time-consuming images.
1492 .PP
1493 A number of filters are available for manipulating picture files.
1494 .I Pfilt
1495 sets the exposure and performs anti-aliasing.
1496 .I Pcompos
1497 composites (cuts and pastes) pictures.
1498 .I Pcond
1499 conditions a picture for a specific display device.
1500 .I Pcomb
1501 performs arbitrary math on one or more pictures.
1502 .I Protate
1503 rotates a picture 90 degrees clockwise.
1504 .I Pflip
1505 flips a picture horizontally, vertically, or both (180 degree rotation).
1506 .I Pvalue
1507 converts a picture to and from simpler formats.
1508 .PP
1509 Pictures may be displayed directly under X11 using the program
1510 .I ximage,
1511 or converted a standard image format.
1512 .I Ra_bmp
1513 converts to and from Microsoft Bitmap images.
1514 .I Ra_ppm
1515 converts to and from Poskanzer Portable Pixmap formats.
1516 .I Ra_ps
1517 converts to PostScript color and greyscale formats.
1518 .I Ra_rgbe
1519 converts to and from Radiance uncompressed picture format.
1520 .I Ra_t16
1521 converts to and from Targa 16 and 24-bit image formats.
1522 .I Ra_t8
1523 converts to and from Targa 8-bit image format.
1524 .I Ra_tiff
1525 converts to and from TIFF.
1526 .I Ra_xyze
1527 converts to and from Radiance CIE picture format.
1528 .NH 1
1529 License
1530 .PP
1531 .DS
1532 The Radiance Software License, Version 1.0
1534 Copyright (c) 1990 - 2008 The Regents of the University of California,
1535 through Lawrence Berkeley National Laboratory. All rights reserved.
1537 Redistribution and use in source and binary forms, with or without
1538 modification, are permitted provided that the following conditions
1539 are met:
1541 1. Redistributions of source code must retain the above copyright
1542 notice, this list of conditions and the following disclaimer.
1544 2. Redistributions in binary form must reproduce the above copyright
1545 notice, this list of conditions and the following disclaimer in
1546 the documentation and/or other materials provided with the
1547 distribution.
1549 3. The end-user documentation included with the redistribution,
1550 if any, must include the following acknowledgment:
1551 "This product includes Radiance software
1552 (
1553 developed by the Lawrence Berkeley National Laboratory
1554 ("
1555 Alternately, this acknowledgment may appear in the software itself,
1556 if and wherever such third-party acknowledgments normally appear.
1558 4. The names "Radiance," "Lawrence Berkeley National Laboratory"
1559 and "The Regents of the University of California" must
1560 not be used to endorse or promote products derived from this
1561 software without prior written permission. For written
1562 permission, please contact [email protected].
1564 5. Products derived from this software may not be called "Radiance",
1565 nor may "Radiance" appear in their name, without prior written
1566 permission of Lawrence Berkeley National Laboratory.
1571 DISCLAIMED. IN NO EVENT SHALL Lawrence Berkeley National Laboratory OR
1580 .DE
1581 .NH 1
1582 Acknowledgements
1583 .PP
1584 This work was supported by the Assistant Secretary of Conservation
1585 and Renewable Energy, Office of Building Energy Research and
1586 Development, Buildings Equipment Division of the U.S. Department of
1587 Energy under Contract No. DE-AC03-76SF00098.
1588 .PP
1589 Additional work was sponsored by the Swiss federal government
1590 under the Swiss LUMEN Project and was
1591 carried out in the Laboratoire d'Energie Solaire (LESO Group) at
1592 the Ecole Polytechnique Federale de Lausanne (EPFL University)
1593 in Lausanne, Switzerland.
1594 .NH 1
1595 References
1596 .LP
1597 Wang, Taoning, Gregory Ward, Eleanor Lee,
1598 ``Efficient modeling of optically-complex, non-coplanar
1599 exterior shading: Validation of matrix algebraic methods,''
1600 .I "Energy & Buildings",
1601 vol. 174, pp. 464-83, Sept. 2018.
1602 .LP
1603 Lee, Eleanor S., David Geisler-Moroder, Gregory Ward,
1604 ``Modeling the direct sun component in buildings using matrix
1605 algebraic approaches: Methods and validation,''
1606 .I Solar Energy,
1607 vol. 160, 15 January 2018, pp 380-395.
1608 .LP
1609 Ward, G., M. Kurt & N. Bonneel,
1610 ``Reducing Anisotropic BSDF Measurement to Common Practice,''
1611 .I Workshop on Material Appearance Modeling,
1612 2014.
1613 .LP
1614 McNeil, A., C.J. Jonsson, D. Appelfeld, G. Ward, E.S. Lee,
1615 ``A validation of a ray-tracing tool used to generate
1616 bi-directional scattering distribution functions for
1617 complex fenestration systems,''
1618 .I "Solar Energy",
1619 98, 404-14, November 2013.
1620 .LP
1621 Ward, G., R. Mistrick, E.S. Lee, A. McNeil, J. Jonsson,
1622 ``Simulating the Daylight Performance of Complex Fenestration Systems
1623 Using Bidirectional Scattering Distribution Functions within Radiance,''
1624 .I "Leukos",
1625 7(4),
1626 April 2011.
1627 .LP
1628 Cater, K., A. Chalmers, G. Ward,
1629 ``Detail to Attention: Exploiting Visual Tasks for Selective Rendering,''
1630 .I "Eurograhics Symposium on Rendering",
1631 June 2003.
1632 .LP
1633 Ward, G., Elena Eydelberg-Vileshin,
1634 ``Picture Perfect RGB Rendering Using Spectral Prefiltering and
1635 Sharp Color Primaries,''
1636 13th Eurographics Workshop on Rendering, P. Debevec and
1637 S. Gibson (Editors), June 2002.
1638 .LP
1639 Ward, G. and M. Simmons,
1640 ``The Holodeck Ray Cache: An Interactive Rendering System for Global
1641 Illumination in Nondiffuse Environments,''
1642 .I "ACM Transactions on Graphics,"
1643 18(4):361-98, October 1999.
1644 .LP
1645 Larson, G.W., H. Rushmeier, C. Piatko,
1646 ``A Visibility Matching Tone Reproduction Operator for High Dynamic
1647 Range Scenes,''
1648 .I "IEEE Transactions on Visualization and Computer Graphics",
1649 3(4), 291-306, December 1997.
1650 .LP
1651 Ward, G.,
1652 ``Making Global Illumination User Friendly,''
1653 .I "Sixth Eurographics Workshop on Rendering",
1654 proceedings to be published by Springer-Verlag,
1655 Dublin, Ireland, June 1995.
1656 .LP
1657 Rushmeier, H., G. Ward, C. Piatko, P. Sanders, B. Rust,
1658 ``Comparing Real and Synthetic Images: Some Ideas about Metrics,''
1659 .I "Sixth Eurographics Workshop on Rendering",
1660 proceedings to be published by Springer-Verlag,
1661 Dublin, Ireland, June 1995.
1662 .LP
1663 Ward, G.,
1664 ``The Radiance Lighting Simulation and Rendering System,''
1665 .I "Computer Graphics",
1666 Orlando, July 1994.
1667 .LP
1668 Rushmeier, H., G. Ward,
1669 ``Energy-Preserving Non-Linear Filters,''
1670 .I "Computer Graphics",
1671 Orlando, July 1994.
1672 .LP
1673 Ward, G.,
1674 ``A Contrast-Based Scalefactor for Luminance Display,''
1675 .I "Graphics Gems IV",
1676 Edited by Paul Heckbert,
1677 Academic Press 1994.
1678 .LP
1679 Ward, G.,
1680 ``Measuring and Modeling Anisotropic Reflection,''
1681 .I "Computer Graphics",
1682 Chicago, July 1992.
1683 .LP
1684 Ward, G., P. Heckbert,
1685 ``Irradiance Gradients,''
1686 .I "Third Annual Eurographics Workshop on Rendering",
1687 to be published by Springer-Verlag, held in Bristol, UK, May 1992.
1688 .LP
1689 Ward, G.,
1690 ``Adaptive Shadow Testing for Ray Tracing,''
1691 .I "Second Annual Eurographics Workshop on Rendering",
1692 to be published by Springer-Verlag, held in Barcelona, SPAIN, May 1991.
1693 .LP
1694 Ward, G.,
1695 ``Visualization,''
1696 .I "Lighting Design and Application",
1697 Vol. 20, No. 6, June 1990.
1698 .LP
1699 Ward, G., F. Rubinstein, R. Clear,
1700 ``A Ray Tracing Solution for Diffuse Interreflection,''
1701 .I "Computer Graphics",
1702 Vol. 22, No. 4, August 1988.
1703 .LP
1704 Ward, G., F. Rubinstein,
1705 ``A New Technique for Computer Simulation of Illuminated Spaces,''
1706 .I "Journal of the Illuminating Engineering Society",
1707 Vol. 17, No. 1, Winter 1988.