[Radiance-general] Radiance, POV-Ray and parallel global illumination?

[George Pantazopoulos]

Hello all,
	
	I am a programmer working with the POV-Ray raytracer. As you may know, for 
global illumination, POV-Ray uses a version of the irradiance caching 
algorithm from Mr. Ward's paper "A Ray Tracing Solution for Diffuse 
Interreflection" (Ward, Rubenstein, and Clear). Presumably Radiance uses a 
similar, but more advanced version of the same algorithm for its global 
illumination simulation.

	I'm trying to get parallel rendering working, but there is a problem. If 
the image is divided into tiles, and rendered with POV-Ray and global 
illumination, each finished tile has a different basic brightness level. 
And when the final image is reassembled from the tiles, the effect is like 
a checkerboard or patchwork. In short, it ruins the final image. Apparently 
each render slave *needs* to have the entire scene octree available to it, 
somehow. There has been an effort to share the octree data with the other 
slaves as soon as it is generated, however this is only partially 
successful and does not always suppress the artifacts I mentioned. (Here is 
a link to the pvmegapov page http://www.wozzeck.net/images/pmp/ )

	I'm wondering if Radiance handles this problem in a fundamentally 
different way, which I could learn from. Some basic parallel Radiance info 
I read did not mention this problem at all, so hopefully you guys already 
have a solution. Any suggestions would be most appreciated!


Thanks,
George Pantazopoulos