[Radiance-general] Noisy irradiance rendering from glow materials

[Andy McNeil]

Hello,

> In an attempt to combat this I tried adding a –ds 0.02 option. This multiplied rendering time by a factor of 5 but resulted in no visible changes (result3.jpg).


In source.h the variable MAXSPART sets the maximum number of source partitions.  Currently it is set to 64.  The end wall of your house is divided into 8x8 partitions which explains the eight hotspots on the ground.  The surfaces of the tower is probably divided into 2x32 divisions since it is slender, hence two hotspots.  increasing -ds won't divide the sources any further than the coded maximum.

But if the surfaces are already fully subdivided then why did computation time increase?  The source division is done separately for each ray.   When computing irradiance on the ground further away from the source (beyond the hotspots) changing -ds will increase the number of source subdivisions.   This is why you experienced increased computation time but the same results.

So instead of changing -ds you would have been better off changing MASXPART and recompiling Radiance.  But don't do this.  Greg's suggestion to use -ab 1 and glow surfaces is more efficient and easier.  

Andy
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