Tom Melly wrote:
> 
> I'm somewhat confused by the different results shown below for BoxA and
> BoxB. Both boxes are clear, below the camera and light and filled with the
> same scattering media. BoxA, which is a shallow box, behaves as I expect -
> the light is scattered, some back towards the camera, and hence shows up as
> white. BoxB, which is much deeper, shows up as black (with white spots in
> ordinary POV, solid black in MegaPOV). I don't understand why the depth of
> the box has an impact on scattering media in this situation. After all, if I
> look at a cloud, it shows as white irrespective of the physical thickness of
> the cloud (provided the cloud is not too thin).
> 
	With the deeper box, nearly all samples are taken in the
middle of the box where all the light from the light_source
has been absorbed while going in. In standard POV, samples
are taken at random, so for some points you've got a fair
chance of having a sample that's taken near enough the side
to be lighted. In MegaPOV with method 2 or 3, the samples
are regularly spaced and all are taken inside.
	If you push the samples count waaayyy up, you'll notice
that the effect diminishes... Another solution is to add
another box completely transparent, hollow, shadowless...
just inside your container to make POV take samples near the
sides:

#declare BoxB = // completely black (with white spots in
POV, pure black in MP)
union { // <-----------Add this
box
{
  <-10000, -10000, -10000>
  < 10000,  0,  10000>
  pigment{rgbf<1,1,1,1>}
  hollow on
  interior{media{Plain_White_Scattering_Media}}
}
box {  // <-----------Add the following lines
  <-9999, -9999, -9999>, < 9999, -1, 9999>
  pigment { rgbf 1 }
  hollow
  no_shadow
}

		Jerome
-- 

* Doctor Jekyll had something * mailto:ber### [at] inamecom
* to Hyde...                  * http://www.enst.fr/~jberger
*******************************

Post a reply to this message