[Radiance-general] Reduce rtrace runtime

[Greg Ward]

The options I am recommending are more recent than RwR, which was current as of 1998.  Path tracing is faster for computing just a few points like this, especially in the presence of venetian blinds.  The negative value for the -lr option is discussed in my presentation from the 2005 Radiance workshop, I discussed these options as they were added to release 3.7:

	http://www.radiance-online.org/radiance-workshop4/cd/website/PDF/Ward_talk1.pdf

Best,
-Greg

> From: Jia Hu <hujia06 at gmail.com>
> Date: August 30, 2010 7:36:34 PM PDT
> 
> Hello Greg:
>  
> Because there are blinds in the office and the rays are only from the outside sky (no light source in the office), is your approach still accurate enough in this case? I am not familiar with this approach. Does your book, Rendering with Radiance, have some introductions to such options as "lr" "lw". I checked the last several chapters and did not find "lr" and "lw".
> Thanks,
> Jia
> On Mon, Aug 30, 2010 at 9:55 PM, Greg Ward <gregoryjward at gmail.com> wrote:
> Computing seven bounces (-ab 7) is very expensive, even for a small number of points.  You end up filling the indirect irradiance cache, which takes some time even on 4 processors.  I would recommend either reducing the number of bounces, or taking advantage of a path tracing approach like so:
> 
>        rtrace -w -h -I -ab 7 -n 4  -ad 2048 -as 0 -aa 0 -lw 1e-5 -lr -10 -u+ office.oct < points.inp
> 
> Setting -aa 0 and -lw 1e-4 limits the number of paths to roughly 100,000 per point, which should run pretty quickly while maintaining accuracy.
> 
> Best,
> -Greg
> 
>