[Radiance-general] rtrace output searching for secondary sources

[timhanson at lizzy.com.au]

Hi,

I am using the following rtrace command :

rtrace -dr 1 -lr 1 -dp 0 -ds 0.02 -dj 0 -lw 0 -dc 1 -st 0 -ab 0 -I+  
-h- -w- -otopn model.oct < singlepoint.pts >> output.out

... to output direct rays from a single gridpoint to an omni light  
source in a room of mirrors.

The intention is to find all the locations of the reflection points  
(of the secondary sources) on each wall from the point of view of the  
gridpoint.  I've written a routine which reads in all the rays,  
filters them and outputs the reflection point x y z coordinates.

The gridpoint is simply :

x y z 0 0 1 indicating an upward direction for the rtrace 'receiver'

The problem I have is that rtrace doesn't output the reflection rays  
if the z-coordinate of the light source is within a small distance  
above the z-coordinate of the gridpoint.  i.e. some reflection rays  
are not output if they are near to, and of course above, the height of  
the gridpoint.

I can understand this may be something to do with the cosine of the  
incident angle and that a threshold isn't reached which therefore  
doesn't output the reflection ray, but I have set -st 0, and I've set  
all the other parameters I can think of to their maximum accuracy.

By setting the property of the mirrors to :
void mirror walls


3 100 100 100  <--- i.e. reflect 100 times the incident intensity

this helped a little, but by increasing the 100 100 100 further and  
further still didn't solve the problem.

If there is anyone who has any ideas, without having to set up each  
grid point for all directions (not just 0 0 1)  - as this produces  
multiple outputs for the same reflection points - any suggestions  
would be much appreciated.

Thanks very much,

Tim