[Radiance-general] radiance graph

[Raphael Compagnon]

Hello,

A few years ago I did similar things as you are doing. Here are some 
advices you may find useful:

At 11.03.2005 15:35, you wrote:
>The technique I used is simple, I have been using the following commandline:
>
>ximage trace.pic | rtrace -ab 1 -ds 0.2 -dr 6  -dt 1 -otodp -h -x 1 -i
>ok.oct  > raytrace_sample.dmp

You may have noticed that rays which are directed towards source objects 
(e.g. the sky hemisphere) get point coordinates that are in fact the origin 
(0,0,0). This leads to many rays wrongly directed to the origin instead of 
going in the right direction. The solution I found is to filter the rtrace 
output just to ignore these rays. This can be done using rcalc like this:
ximage trace.pic | rtrace -ab 1 -ds 0.2 -dr 6  -dt 1 -otodp -h -x 1 -i 
ok.oct |  \
rcalc -e 'abs(x)=if(x,x,-x);cond=abs($7)+abs($8)+abs($9)' > raytrace_sample.dmp

>To make the graph more clear, it would be interesting to color them for
>instance accordingly to how often a ray bounced. What would be a good way
>for scripting rtrace such that I'll be able to do so?

I just outline herefater a technique that works for a scene with opaque 
diffusers only. You may also adapt this technique to other type of materials.

First define a new plastic with a .9 reflectance:
void plastic new_mat
0
0
5 .9 .9 .9 0 0

Then apply this new material to your scene file:

pfilt -m new_mat original_scene.rad >new_scene.rad

Alter also all light emitting types (i.e. glow, light, illum) of your scene 
so that their R,G,B values are 1

By doing so the radiance values that is attached to a single ray will be 
0.9^n with n the number of bounces it has encoutered.

Then add to your rtrace output the value of each rays using option -otodpv 
(this last v is the thing you need!)

The output of rtrace can then be processed using rcalc to retrieve the 
number of bounces n that you may then use to whatever you need:
rtrace -otodpv... | rcalc -e 'n=$10/log(0.9); ... '

Raphael Compagnon