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.\" RCSid "$Id$" |
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.\" Print using the -ms macro package |
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.DA 07/10/2016 |
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.DA 12/09/2024 |
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.LP |
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.tl """Copyright \(co 2017 Regents, University of California |
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.tl """Copyright \(co 2024 Regents, University of California |
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.sp 2 |
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.TL |
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The |
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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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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 WGMDfunc |
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.PP |
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WGMDfunc is a more programmable version of trans2, |
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with separate modifier paths and variables to control each component. |
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(WGMD stands for Ward-Geisler-Moroder-Duer, which is the basis for |
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this empirical model, similar to the previous ones beside Ashik2.)\0 |
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The specification of this material is given below. |
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.DS |
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mod WGMDfunc id |
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13+ rs_mod rs rs_urough rs_vrough |
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ts_mod ts ts_urough ts_vrough |
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td_mod |
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ux uy uz funcfile transform |
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0 |
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9+ rfdif gfdif bfdif |
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rbdif gbdif bbdif |
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rtdif gtdif btdif |
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A10 .. |
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.DE |
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The sum of specular reflectance ( |
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.I rs |
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), specular transmittance ( |
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.I ts |
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), diffuse reflectance ( |
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.I "rfdif gfdif bfdif" |
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for front and |
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.I "rbdif gbdif bbdif" |
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for back) |
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and diffuse transmittance ( |
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.I "rtdif gtdif btdif" |
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) should be less than 1 for each |
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channel. |
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.PP |
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Unique to this material, separate modifier channels are |
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provided for each component. |
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The main modifier is used on the diffuse reflectance, both |
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front and back. |
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The |
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.I rs_mod |
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modifier is used for specular reflectance. |
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If "void" is given for |
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.I rs_mod, |
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then the specular reflection color will be white. |
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The special "inherit" keyword may also be given, in which case |
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specular reflectance will share the main modifier. |
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This behavior is replicated for the specular transmittance modifier |
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.I ts_mod, |
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which has its own independent roughness expressions. |
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Finally, the diffuse transmittance modifier is given as |
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.I td_mod, |
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which may also be "void" or "inherit". |
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Note that any spectra or color for specular components must be |
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carried by the named modifier(s). |
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.PP |
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The main advantage to this material over BRTDfunc and |
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other programmable types described below is that the specular sampling is |
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well-defined, so that all components are fully computed. |
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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 sBSDF |
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.UL aBSDF |
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.PP |
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The sBSDF material is identical to the BSDF type with two important |
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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 sBSDF is assumed to have some specular through component, which |
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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 sBSDF id |
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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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.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 sBSDF. |
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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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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 extrema of the |
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spectral range in nanometers. |
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Subsequent real values correspond to multipliers at each wavelength. |
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The nmA wavelength may be greater or less than nmB, |
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but they may not be equal, and their ordering matches |
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the order 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+ sfunc 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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set in the evaluation context. |
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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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.LP |
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+ |
.UL Specdata |
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+ |
.PP |
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Specdata is like brightdata and colordata, but with more |
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than 3 specular samples. |
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.DS |
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mod specdata id |
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3+n+ |
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func datafile |
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funcfile x1 x2 .. xn transform |
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0 |
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+ |
m A1 A2 .. Am |
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+ |
.DE |
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The data file must have one more dimension than the coordinate |
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variable count, as this final dimension corresponds to the covered |
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spectrum. |
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The starting and ending wavelengths are specified in "datafile" |
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as well as the number of spectral samples. |
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The function "func" will be called with two parameters, the |
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interpolated spectral value for the current coordinate and the |
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associated wavelength. |
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If the spectrum is broken into 12 components, then 12 calls |
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will be made to "func" for the relevant ray evaluation. |
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.LP |
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.UL Specpict |
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+ |
.PP |
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Specpict is a special case of specdata, where the pattern is |
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a hyperspectral image stored in the common-exponent file format. |
| 1348 |
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The dimensions of the image data are determined by the picture |
| 1349 |
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just as with the colorpict primitive. |
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.DS |
| 1351 |
+ |
mod specpict id |
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+ |
5+ |
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func specfile |
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+ |
funcfile u v transform |
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+ |
0 |
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+ |
m A1 A2 .. Am |
| 1357 |
+ |
.DE |
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+ |
The function "func" is called with the interpolated pixel value |
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and the wavelength sample in nanometers, the same as specdata, |
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with as many calls made as there are components in "specfile". |
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.NH 3 |
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Mixtures |
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.PP |
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in Lausanne, Switzerland. |
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.NH 1 |
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References |
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+ |
.LP |
| 1763 |
+ |
Ward, Gregory J., Bruno Bueno, David Geisler-Moroder, |
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+ |
Lars O. Grobe, Jacob C. Jonsson, Eleanor |
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+ |
S. Lee, Taoning Wang, Helen Rose Wilson, |
| 1766 |
+ |
``Daylight Simulation Workflows Incorporating |
| 1767 |
+ |
Measured Bidirectional Scattering Distribution Functions,'' |
| 1768 |
+ |
.I "Energy & Buildings", |
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+ |
Vol. 259, No. 111890, 2022. |
| 1770 |
+ |
.LP |
| 1771 |
+ |
Wang, Taoning, Gregory Ward, Eleanor Lee, |
| 1772 |
+ |
``Efficient modeling of optically-complex, non-coplanar |
| 1773 |
+ |
exterior shading: Validation of matrix algebraic methods,'' |
| 1774 |
+ |
.I "Energy & Buildings", |
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+ |
vol. 174, pp. 464-83, Sept. 2018. |
| 1776 |
|
.LP |
| 1777 |
|
Lee, Eleanor S., David Geisler-Moroder, Gregory Ward, |
| 1778 |
|
``Modeling the direct sun component in buildings using matrix |
