| 92 |
|
ed epsilon_d set diffuse emittance for current material |
| 93 |
|
rs rho_s alpha_r set specular reflectance for current material |
| 94 |
|
ts tau_s alpha_t set specular transmittance for current material |
| 95 |
+ |
ir n_real n_imag set index of refraction for current material |
| 96 |
|
o [name] begin/end object context |
| 97 |
|
f v1 v2 v3 .. polygon using current material, spec. vertices |
| 98 |
|
sph vc radius sphere |
| 239 |
|
|
| 240 |
|
The sum of the diffuse and specular reflectances and transmittances |
| 241 |
|
must be strictly less than one (with no negative values, obviously). |
| 242 |
+ |
These values are assumed to be measured at normal incidence. If an |
| 243 |
+ |
index of refraction is given, this may modify the balance between |
| 244 |
+ |
diffuse and specular reflectance at other incident angles. If the |
| 245 |
+ |
material is one-sided (see below), then it may be a dielectric interface. |
| 246 |
+ |
In this case, the specular transmittance given is that which would be |
| 247 |
+ |
measured at normal incidence for a pane of the material 5 mm thick. |
| 248 |
+ |
This is important for figuring the actual transmittance for non-planar |
| 249 |
+ |
geometries assuming a uniformly absorbing medium. If the index of |
| 250 |
+ |
refraction has an imaginary part, then the surface is a metal and this |
| 251 |
+ |
implies other properties according to physics. The default index of |
| 252 |
+ |
refraction is that of a vacuum, i.e. (1,0). |
| 253 |
|
|
| 254 |
|
The object entity establishes a hierarchical context, consisting of |
| 255 |
|
this identifier and all those preceding. It has no real meaning except |
| 257 |
|
under a descriptive name for improved file readability. |
| 258 |
|
|
| 259 |
|
Surfaces are two-sided unless the "sides" entity is used to set the |
| 260 |
< |
number of sides for a material to one. If a surfaces is one-sided, |
| 260 |
> |
number of sides for a material to one. If a surface is one-sided, |
| 261 |
|
then it appears invisible when viewed from the back side. This means |
| 262 |
|
that a transmitting object will affect the light coming in through the |
| 263 |
|
front surface and ignore the characteristics of the back surface. As |
| 264 |
< |
long as the characteristics are the same, the results should be |
| 265 |
< |
correct. If the rendering technique does not allow for one-sided |
| 264 |
> |
long as the transmission characteristics are the same, the results should |
| 265 |
> |
be correct. If the rendering technique does not allow for one-sided |
| 266 |
|
surfaces, an approximately correct result can be obtained for one-sided |
| 267 |
|
transmitting surfaces by using the square root of the given tau_s and |
| 268 |
|
half the given alpha_t. If a rendering technique does not permit |
