[Radiance-general] ambient resolution and memory

[Gregory J. Ward]

Hi Lars,

Just finished with the Radiance workshop, so catching up on e-mails.   
This is an interesting thread...

>> How many ambient bounces are you using? I think for an interior  
>> scene with illums at the window openings you should be able to set  
>> -ab 1....
>
> Yes, I am playing with 2 bounces at the moment, but then it is  
> impossible to get results. I used -ab 1 before. I already have  
> exlde lists for the ambient calculation. The glow for illumination  
> is a nice idea, if I just want to see the position of light  
> sources. But if they are to illuminate the scene?

The "glow" type with an effective radius still illuminates the scene  
correctly.  Base your radius on the distance over which you expect  
your sources to be important.  Past that distance, they will be  
considered as "indirect" sources.  One important caveat:  the smaller  
and brighter they are, the more artifacts you will see from them if  
your radius is too small.

Another tip to reduce calculation time if you are using a recent  
version of Radiance (3.6 or later) is that large surfaces in the main  
octree will be tracked in the shadow cache.  Neither instances nor  
meshes will work as obstructors, so if you must instantiate geometry,  
leave at least some large occluders in the main octree to help in the  
shadow cache.

> I was thinking of making even heavier use of mkillum. First,  
> bundling the light sources, so that there will be hundreds, not  
> thousand, at least in the indirect calculation. Than it may make  
> sense to divide the interior with illum panes, so that e.g. the  
> light contributed from the galleries to the main room is  
> precomputed by mkillum. Finally I may end by dividing the whole  
> scene in virtual rooms seperated by illum panes?

It's a curious idea.  I'm not sure whether or not it will help, but  
I'd love to see the results.

> Is there a patch for current radiance that allows an alternative  
> modifier (like void) for the indirect calculation? That is  
> available in Radzilla and might be very helpful, as I have  
> colorpict maps on most surfaces.

There is no such hack.  It's not really physical, is the problem.

One other note -- you might try setting -ar 0 in your case.  If you  
have really large and small geometry that require enormous -ar  
settings, you may be better off without it.  Alternatively, you can  
try excluding your ground plane from the indirect calculation with a - 
ae option.  You can have a close-up ground plane that you include to  
catch the indirect from the building, then forget it outside a  
certain distance.  This will avoid the placement of excess indirect  
values where nothing really is going on.

-Greg