Am 13.03.2017 um 11:57 schrieb muyu:
> Hi,
> 
> I would like to simulate the radiative transfer in 3D crop canopy using Pov-ray.
> We can have the optical properties of each surface (transmitance and
> reflectance/diffuse). In order to simulate the multi-scattering, I would like to
> use radiosity.
> 
> 1) I can set the transmitance by rgbt(0,1,0,transmitance). Transmitance is the
> same for all the three color chanels? This is not realistic for most cases.

Alternatively (or in addition) you can use filtering transparency, by
specifying the pigment as `rgbf <R,G,B,Filter>` (or `rgbft
<R,G,B,Filter,Trans>`). This will give you an effective transmissive
component of `<R,G,B>*Filter` (or `<R,G,B>*Filter+<1,1,1>*Trans`).

Be aware that if you use solid shapes the effect will be applied twice
(once at each interface).

Also note that this type of transmittance does not account for any
scattering. For that you would have to use a different mechanism: Media
(requires solid shapes), subsurface light transport (requires solid
shapes), or backside diffuse illumination (requires non-solid shapes).
For the latter you would specify `finish{diffuse DFront,DBack}`, giving
you a diffuse reflectivity of `Pigment*DFront` and a diffuse
transmittance of `Pigment*DBack`.

> 2) diffuse can be set by finish{diffuse df}. But I do not know how this diffuse
> impact the surface color? rgb(0,1,0)*diffuse?

Yes, the `diffuse` term is multiplied by the nominal pigment colour.

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