[Radiance-general] -ar, -ad, -as, ahh $#*@!

[Greg Ward]

Hi Rob,

This seems to be a classic example of where you just can't rely on the 
interreflection calculation in Radiance to solve your problem for you.  
The basic assumption in this approximation is that the indirect 
illumination varies slowly over surfaces, which clearly isn't the case 
in this scene.

Solution: you need to apply mkillum to create pseudo light sources 
(imposters) for your indirect luminaires.  To do so, put a shallow box 
with an open top around a single ceiling-mounted light source (5 
rectangles) and use the "void" modifer for these, making sure they face 
out into your room.  Let's say you called this file "light_in.rad".  
Using either the octree for your room or a reduced one that just has 
that one light source switched on (better), you would run mkillum thus:

% mkillum -ab 1 -ad 512 -as 256 -ar 16 < light_in.rad > light_out.rad

In addition to creating the light_out.rad file, mkillum will generate 5 
data files containing the computed output distribution for your 
luminaire.  You may then take the light_out.rad and use an array 
transform to place it over all the light sources in your scene.  For 
the sake of calculational efficiency, I recommend that you also change 
the light primitives in your original luminaire files to the "glow" 
type with an effective distance equal to the diagonal of your luminaire 
dimension, so as to avoid sending shadow rays to these sources 
unnecessarily.

The net result should be a fast and accurate rendering of your space.

-Greg

> From: Rob Guglielmetti <rpg@rumblestrip.org>
> Date: Tue Sep 9, 2003  8:20:52  AM US/Pacific
>
> Hi all,
>
> Struggling with ies lights & ambient parameters, and blotchy 
> renderings.  For those interested, have a look at this:
>
> http://www.rumblestrip.org/rad/rad_01.html
>
> ...and then report back on this frequency, if you have any 
> suggestions.  TIA
>
> ----
>
>      Rob Guglielmetti