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MATERIALS AND GEOMETRY FORMAT |
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SCCSid "$SunId$ LBL" |
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RCSid "$Id$" |
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Introduction |
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============ |
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ed epsilon_d set diffuse emittance for current material |
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rs rho_s alpha_r set specular reflectance for current material |
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ts tau_s alpha_t set specular transmittance for current material |
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ir n_real n_imag set index of refraction for current material |
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o [name] begin/end object context |
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f v1 v2 v3 .. polygon using current material, spec. vertices |
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sph vc radius sphere |
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The sum of the diffuse and specular reflectances and transmittances |
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must be strictly less than one (with no negative values, obviously). |
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These values are assumed to be measured at normal incidence. If an |
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index of refraction is given, this may modify the balance between |
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diffuse and specular reflectance at other incident angles. If the |
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material is one-sided (see below), then it may be a dielectric interface. |
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In this case, the specular transmittance given is that which would be |
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measured at normal incidence for a pane of the material 5 mm thick. |
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This is important for figuring the actual transmittance for non-planar |
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geometries assuming a uniformly absorbing medium. If the index of |
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refraction has an imaginary part, then the surface is a metal and this |
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implies other properties according to physics. The default index of |
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refraction is that of a vacuum, i.e. (1,0). |
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The object entity establishes a hierarchical context, consisting of |
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this identifier and all those preceding. It has no real meaning except |
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under a descriptive name for improved file readability. |
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Surfaces are two-sided unless the "sides" entity is used to set the |
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number of sides for a material to one. If a surfaces is one-sided, |
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number of sides for a material to one. If a surface is one-sided, |
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then it appears invisible when viewed from the back side. This means |
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that a transmitting object will affect the light coming in through the |
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front surface and ignore the characteristics of the back surface. As |
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long as the characteristics are the same, the results should be |
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correct. If the rendering technique does not allow for one-sided |
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long as the transmission characteristics are the same, the results should |
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be correct. If the rendering technique does not allow for one-sided |
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surfaces, an approximately correct result can be obtained for one-sided |
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transmitting surfaces by using the square root of the given tau_s and |
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half the given alpha_t. If a rendering technique does not permit |