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.\" RCSid "$Id$" |
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.\" Print using the -ms macro package |
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.DA 07/31/2014 |
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.DA 11/13/2023 |
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.LP |
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< |
.tl """Copyright \(co 2014 Regents, University of California |
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.tl """Copyright \(co 2023 Regents, University of California |
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.sp 2 |
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.TL |
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The |
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8 red green blue spec urough vrough trans tspec |
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.DE |
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.LP |
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.UL Ashik2 |
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.PP |
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Ashik2 is the anisotropic reflectance model by Ashikhmin & Shirley. |
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The string arguments are the same as for plastic2, but the real |
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arguments have additional flexibility to specify the specular color. |
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Also, rather than roughness, specular power is used, which has no |
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physical meaning other than larger numbers are equivalent to a smoother |
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surface. |
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Unlike other material types, total reflectance is the sum of |
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diffuse and specular colors, and should be adjusted accordingly. |
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.DS |
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mod ashik2 id |
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4+ ux uy uz funcfile transform |
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0 |
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8 dred dgrn dblu sred sgrn sblu u-power v-power |
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.DE |
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.LP |
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.UL Dielectric |
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.PP |
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A dielectric material is transparent, and it refracts light |
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Unlike other data-driven material types, the BSDF type is fully |
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supported and all parts of the distribution are properly sampled. |
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.LP |
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.UL aBSDF |
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.PP |
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The aBSDF material is identical to the BSDF type with two important |
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differences. |
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First, proxy geometry is not supported, so there is no thickness parameter. |
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Second, an aBSDF is assumed to have some specular through component |
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(the 'a' stands for "aperture"), which |
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is treated specially during the direct calculation and when viewing the |
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material. |
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Based on the BSDF data, the coefficient of specular transmission is |
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determined and used for modifying unscattered shadow and view rays. |
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.DS |
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mod aBSDF id |
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5+ BSDFfile ux uy uz funcfile transform |
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0 |
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0|3|6|9 |
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rfdif gfdif bfdif |
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rbdif gbdif bbdif |
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rtdif gtdif btdif |
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.DE |
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.LP |
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If a material has no specular transmitted component, it is much better |
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to use the BSDF type with a zero thickness than to use aBSDF. |
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.LP |
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.UL Antimatter |
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.PP |
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Antimatter is a material that can "subtract" volumes from other volumes. |
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The first modifier will also be used to shade the area leaving the |
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antimatter volume and entering the regular volume. |
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If mod1 is void, the antimatter volume is completely invisible. |
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Antimatter does not work properly with the material type "trans", |
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and multiple antimatter surfaces should be disjoint. |
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If shading is desired at antimatter surfaces, it is important |
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that the related volumes are closed with outward-facing normals. |
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Antimatter surfaces should not intersect with other antimatter boundaries, |
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and it is unwise to use the same modifier in nested antimatter volumes. |
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The viewpoint must be outside all volumes concerned for a correct |
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rendering. |
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.NH 3 |
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font such as hexbit4x1.fnt, calls for uniform spacing. |
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Reasonable magnitudes for proportional spacing are |
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between 0.1 (for tightly spaced characters) and 0.3 (for wide spacing). |
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.LP |
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.UL Spectrum |
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.PP |
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The spectrum primitive is the most basic type for introducing spectral |
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color to a material. |
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Since materials only provide RGB parameters, spectral patterns |
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are the only way to superimpose wavelength-dependent behavior. |
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.DS |
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mod spectrum id |
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0 |
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0 |
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5+ nmA nmB s1 s2 .. sN |
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.DE |
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The first two real arguments indicate the limits of the covered |
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spectral range in nanometers. |
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Subsequent real values correspond to multipliers in each wavelength band, |
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where the first band goes from nmA to nmA+(nmB-nmA)/N, and N is the |
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number of bands (i.e., the number of real arguments minus 2). |
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The nmA wavelength may be greater or less than the nmB wavelength, |
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but they may not be equal, and their ordering must correspond to |
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the ordering of the spectral values. |
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A minimum of 3 values must be given, which would act |
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more or less the same as a constant RGB multiplier. |
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As with RGB values, spectral quantities normally range between 0 |
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and 1 at each wavelength, or average to 1.0 against a standard |
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sensitivity functions such as V(lambda). |
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The best results obtain when the spectral range and number |
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of samples match rendering options, though resampling will handle |
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any differences, zero-filling wavelenths outside the nmA to nmB |
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range. |
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A warning will be issued if the given wavelength range does not |
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adequately cover the visible spectrum. |
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.LP |
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.UL Specfile |
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.PP |
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The specfile primitive is equivalent to the spectrum type, but |
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the wavelength range and values are contained in a 1-dimensional |
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data file. |
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This may be a more convenient way to specify a spectral color, |
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especially one corresponding to a standard illuminant such as D65 |
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or a library of measured spectra. |
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.DS |
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mod specfile id |
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1 datafile |
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0 |
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0 |
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.DE |
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As with the spectrum type, rendering wavelengths outside the defined |
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range will be zero-filled. |
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Unlike the spectrum type, the file may contain non-uniform samples. |
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.LP |
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.UL Specfunc |
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.PP |
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The specfunc primitive offers dynamic control over a spectral |
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pattern, similar to the colorfunc type. |
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.DS |
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mod specfunc id |
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2+ sval funcfile transform |
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0 |
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2+ nmA nmB A3 .. |
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.DE |
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Like the spectrum primitive, the wavelength range is specified |
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in the first two real arguments, and additional real values are |
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accessible to the sval function. |
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This function is fed a wavelenth sample |
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between nmA and nmB as its only argument, |
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and it returns the corresponding spectral intensity. |
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.NH 3 |
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Mixtures |
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.PP |
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A mixture is a blend of one or more materials or textures and patterns. |
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Blended materials should not be light source types or virtual source types. |
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The basic types are given below. |
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.LP |
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.UL Mixfunc |
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in Lausanne, Switzerland. |
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.NH 1 |
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References |
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.LP |
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Ward, Gregory J., Bruno Bueno, David Geisler-Moroder, |
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Lars O. Grobe, Jacob C. Jonsson, Eleanor |
| 1668 |
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S. Lee, Taoning Wang, Helen Rose Wilson, |
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``Daylight Simulation Workflows Incorporating |
| 1670 |
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Measured Bidirectional Scattering Distribution Functions,'' |
| 1671 |
+ |
.I "Energy & Buildings", |
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Vol. 259, No. 111890, 2022. |
| 1673 |
+ |
.LP |
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Wang, Taoning, Gregory Ward, Eleanor Lee, |
| 1675 |
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``Efficient modeling of optically-complex, non-coplanar |
| 1676 |
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exterior shading: Validation of matrix algebraic methods,'' |
| 1677 |
+ |
.I "Energy & Buildings", |
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vol. 174, pp. 464-83, Sept. 2018. |
| 1679 |
+ |
.LP |
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Lee, Eleanor S., David Geisler-Moroder, Gregory Ward, |
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``Modeling the direct sun component in buildings using matrix |
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algebraic approaches: Methods and validation,'' |
| 1683 |
+ |
.I Solar Energy, |
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vol. 160, 15 January 2018, pp 380-395. |
| 1685 |
+ |
.LP |
| 1686 |
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Ward, G., M. Kurt & N. Bonneel, |
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``Reducing Anisotropic BSDF Measurement to Common Practice,'' |
| 1688 |
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.I Workshop on Material Appearance Modeling, |
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2014. |
| 1690 |
|
.LP |
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McNeil, A., C.J. Jonsson, D. Appelfeld, G. Ward, E.S. Lee, |
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``A validation of a ray-tracing tool used to generate |
