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Revision 1.12 by greg, Fri Jun 1 19:46:07 2007 UTC vs.
Revision 1.40 by greg, Fri Nov 3 17:41:27 2023 UTC

# Line 1 | Line 1
1 < .\" RCSid "$Id"
1 > .\" RCSid "$Id$"
2   .\" Print using the -ms macro package
3 < .DA 10/17/2006
3 > .DA 5/11/2023
4   .LP
5 < .tl """Copyright \(co 2006 Regents, University of California
5 > .tl """Copyright \(co 2023 Regents, University of California
6   .sp 2
7   .TL
8   The
# Line 491 | Line 491 | 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 Heyney-Greenstein function:
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
# Line 622 | Line 622 | mod trans2 id
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 + Unlike other material types, total reflectance is the sum of
634 + diffuse and specular colors, and should be adjusted accordingly.
635 + .DS
636 + mod ashik2 id
637 + 4+ ux uy uz funcfile transform
638 + 0
639 + 8 dred dgrn dblu sred sgrn sblu u-power v-power
640 + .DE
641 + .LP
642   .UL Dielectric
643   .PP
644   A dielectric material is transparent, and it refracts light
# Line 865 | Line 882 | mod transdata id
882   6+ red green blue rspec trans tspec A7 ..
883   .DE
884   .LP
885 + .UL BSDF
886 + .PP
887 + The BSDF material type loads an XML (eXtensible Markup Language)
888 + file describing a bidirectional scattering distribution function.
889 + Real arguments to this material may define additional
890 + diffuse components that augment the BSDF data.
891 + String arguments are used to define thickness for proxied
892 + surfaces and the "up" orientation for the material.
893 + .DS
894 + mod BSDF id
895 + 6+ thick BSDFfile ux uy uz funcfile transform
896 + 0
897 + 0|3|6|9
898 +     rfdif gfdif bfdif
899 +     rbdif gbdif bbdif
900 +     rtdif gtdif btdif
901 + .DE
902 + The first string argument is a "thickness" parameter that may be used
903 + to hide detail geometry being proxied by an aggregate BSDF material.
904 + If a view or shadow ray hits a BSDF proxy with non-zero thickness,
905 + it will pass directly through as if the surface were not there.
906 + Similar to the illum type, this permits direct viewing and
907 + shadow testing of complex geometry.
908 + The BSDF is used when a scattered (indirect) ray hits the surface,
909 + and any transmitted sample rays will be offset by the thickness amount
910 + to avoid the hidden geometry and gather samples from the other side.
911 + In this manner, BSDF surfaces can improve the results for indirect
912 + scattering from complex systems without sacrificing appearance or
913 + shadow accuracy.
914 + If the BSDF has transmission and back-side reflection data,
915 + a parallel BSDF surface may be
916 + placed slightly less than the given thickness away from the front surface
917 + to enclose the complex geometry on both sides.
918 + The sign of the thickness is important, as it indicates whether the
919 + proxied geometry is behind the BSDF surface (when thickness is positive)
920 + or in front (when thickness is negative).
921 + .LP
922 + The second string argument is the name of the BSDF file, which is
923 + found in the usual auxiliary locations.
924 + The following three string parameters name variables for an "up" vector,
925 + which together with the surface normal, define the
926 + local coordinate system that orients the BSDF.
927 + These variables, along with the thickness, are defined in a function
928 + file given as the next string argument.
929 + An optional transform is used to scale the thickness and reorient the up vector.
930 + .LP
931 + If no real arguments are given, the BSDF is used by itself to determine
932 + reflection and transmission.
933 + If there are at least 3 real arguments, the first triplet is an
934 + additional diffuse reflectance for the front side.
935 + At least 6 real arguments adds diffuse reflectance to the rear side of the surface.
936 + If there are 9 real arguments, the final triplet will be taken as an additional
937 + diffuse transmittance.
938 + All diffuse components as well as the non-diffuse transmission are
939 + modified by patterns applied to this material.
940 + The non-diffuse reflection from either side are unaffected.
941 + Textures perturb the effective surface normal in the usual way.
942 + .LP
943 + The surface normal of this type is not altered to face the incoming ray,
944 + so the front and back BSDF reflections may differ.
945 + (Transmission is identical front-to-back by physical law.)\0
946 + If back visibility is turned off during rendering and there is no
947 + transmission or back-side reflection, only then the surface will be
948 + invisible from behind.
949 + Unlike other data-driven material types, the BSDF type is fully
950 + supported and all parts of the distribution are properly sampled.
951 + .LP
952 + .UL aBSDF
953 + .PP
954 + The aBSDF material is identical to the BSDF type with two important
955 + differences.
956 + First, proxy geometry is not supported, so there is no thickness parameter.
957 + Second, an aBSDF is assumed to have some specular through component
958 + (the 'a' stands for "aperture"), which
959 + is treated specially during the direct calculation and when viewing the
960 + material.
961 + Based on the BSDF data, the coefficient of specular transmission is
962 + determined and used for modifying unscattered shadow and view rays.
963 + .DS
964 + mod aBSDF id
965 + 5+ BSDFfile ux uy uz funcfile transform
966 + 0
967 + 0|3|6|9
968 +     rfdif gfdif bfdif
969 +     rbdif gbdif bbdif
970 +     rtdif gtdif btdif
971 + .DE
972 + .LP
973 + If a material has no specular transmitted component, it is much better
974 + to use the BSDF type with a zero thickness than to use aBSDF.
975 + .LP
976   .UL Antimatter
977   .PP
978   Antimatter is a material that can "subtract" volumes from other volumes.
# Line 879 | Line 987 | N mod1 mod2 .. modN
987   The first modifier will also be used to shade the area leaving the
988   antimatter volume and entering the regular volume.
989   If mod1 is void, the antimatter volume is completely invisible.
990 < Antimatter does not work properly with the material type "trans",
991 < and multiple antimatter surfaces should be disjoint.
990 > If shading is desired at antimatter surfaces, it is important
991 > that the related volumes are closed with outward-facing normals.
992 > Antimatter surfaces should not intersect with other antimatter boundaries,
993 > and it is unwise to use the same modifier in nested antimatter volumes.
994   The viewpoint must be outside all volumes concerned for a correct
995   rendering.
996   .NH 3
# Line 1088 | Line 1198 | between 0.1 (for tightly spaced characters) and 0.3 (f
1198   Mixtures
1199   .PP
1200   A mixture is a blend of one or more materials or textures and patterns.
1201 + Blended materials should not be light source types or virtual source types.
1202   The basic types are given below.
1203   .LP
1204   .UL Mixfunc
# Line 1235 | Line 1346 | If no file is needed by a given primitive because all
1346   variables are global, a period (`.') can be given in
1347   place of the file name.
1348   It is also possible to give an expression instead of a straight
1349 < variable name in a scene file, although such expressions should
1350 < be kept simple if possible.
1240 < Also, functions (requiring parameters)
1349 > variable name in a scene file.
1350 > Functions (requiring parameters)
1351   must be given as names and not as expressions.
1352   .PP
1353   Constant expressions are used as an optimization in function
# Line 1401 | Line 1511 | converts a picture to and from simpler formats.
1511   Pictures may be displayed directly under X11 using the program
1512   .I ximage,
1513   or converted a standard image format.
1514 < .I Ra_avs
1515 < converts to and from AVS image format.
1406 < .I Ra_pict
1407 < converts to Macintosh 32-bit PICT2 format.
1514 > .I Ra_bmp
1515 > converts to and from Microsoft Bitmap images.
1516   .I Ra_ppm
1517   converts to and from Poskanzer Portable Pixmap formats.
1410 – .I Ra_pr
1411 – converts to and from Sun 8-bit rasterfile format.
1412 – .I Ra_pr24
1413 – converts to and from Sun 24-bit rasterfile format.
1518   .I Ra_ps
1519   converts to PostScript color and greyscale formats.
1520   .I Ra_rgbe
# Line 1429 | Line 1533 | License
1533   .DS
1534   The Radiance Software License, Version 1.0
1535  
1536 < Copyright (c) 1990 - 2002 The Regents of the University of California,
1536 > Copyright (c) 1990 - 2008 The Regents of the University of California,
1537   through Lawrence Berkeley National Laboratory.   All rights reserved.
1538  
1539   Redistribution and use in source and binary forms, with or without
# Line 1491 | Line 1595 | the Ecole Polytechnique Federale de Lausanne (EPFL Uni
1595   in Lausanne, Switzerland.
1596   .NH 1
1597   References
1598 + .LP
1599 + Ward, Gregory J., Bruno Bueno, David Geisler-Moroder,
1600 + Lars O. Grobe, Jacob C. Jonsson, Eleanor
1601 + S. Lee, Taoning Wang, Helen Rose Wilson,
1602 + ``Daylight Simulation Workflows Incorporating
1603 + Measured Bidirectional Scattering Distribution Functions,''
1604 + .I "Energy & Buildings",
1605 + Vol. 259, No. 111890, 2022.
1606 + .LP
1607 + Wang, Taoning, Gregory Ward, Eleanor Lee,
1608 + ``Efficient modeling of optically-complex, non-coplanar
1609 + exterior shading: Validation of matrix algebraic methods,''
1610 + .I "Energy & Buildings",
1611 + vol. 174, pp. 464-83, Sept. 2018.
1612 + .LP
1613 + Lee, Eleanor S., David Geisler-Moroder, Gregory Ward,
1614 + ``Modeling the direct sun component in buildings using matrix
1615 + algebraic approaches: Methods and validation,''
1616 + .I Solar Energy,
1617 + vol. 160, 15 January 2018, pp 380-395.
1618 + .LP
1619 + Ward, G., M. Kurt & N. Bonneel,
1620 + ``Reducing Anisotropic BSDF Measurement to Common Practice,''
1621 + .I Workshop on Material Appearance Modeling,
1622 + 2014.
1623 + .LP
1624 + McNeil, A., C.J. Jonsson, D. Appelfeld, G. Ward, E.S. Lee,
1625 + ``A validation of a ray-tracing tool used to generate
1626 + bi-directional scattering distribution functions for
1627 + complex fenestration systems,''
1628 + .I "Solar Energy",
1629 + 98, 404-14, November 2013.
1630 + .LP
1631 + Ward, G., R. Mistrick, E.S. Lee, A. McNeil, J. Jonsson,
1632 + ``Simulating the Daylight Performance of Complex Fenestration Systems
1633 + Using Bidirectional Scattering Distribution Functions within Radiance,''
1634 + .I "Leukos",
1635 + 7(4),
1636 + April 2011.
1637   .LP
1638   Cater, K., A. Chalmers, G. Ward,
1639   ``Detail to Attention: Exploiting Visual Tasks for Selective Rendering,''

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