[Radiance-general] rendering parameters

[John S. An]

I was wondering if I could get some input from the experienced Radiance 
users out there regarding rendering parameters.  I am currently 
rendering an extremely basic room (13.5'x13.5'x14') with one indirect 
light fixture.  However, accuracy is extremely important.  So I am in 
the process of running test runs to see what would be the optimal 
rendering parameters within the time limit I have.

I had been getting blotchy results, so I have been doubling the -ad 
parameter.  My most recent rendering parameters were:

-i -t 600 -dt 0.04 -dc 1 -ds 0.01 -dj 0.6 -dr 3 -dp 4096 -st 0.01 -sj 1 
-av 0 0 0 -aw 0 -ab 3 -ad 4096 -as 2048 -ar 256 -aE ../ambient_exclude 
-ms 2.7 -lr 12 -lw 0.0005 -aa 0.04 -af b_b_m.amb -ps 1 -pt 0.04 -x 512 
-y 512 -pa 0

I did an overture rendering at -x 64 -y 64 prior to creating the image 
at 512x512.

I am, still getting what I feel to be significant blotchiness.  The 
image can be seen at:
http:/homepage.mac.com/jsan

So, my questions are:
Are there any immediate red-flags you see in my rendering parameters 
that seem incorrect?
Do I simply need to keep increasing the -ad to get better results, or 
would lowering the -pt help both the visual and calculation accuracy?
If I pfilt the image with -x /2 -y /2, will that merge the values of 
the pixels enough to make the values at each pixel relatively accurate?

Just as background, this image took about 12 hours to render (with the 
overture calculations) using rpiece on a dual G5 Macintosh with 1.5 GB 
of RAM and a 2.24 P4 with 1 GB of RAM.  I have about 200 similar 
situations to run (more light fixtures, larger room, etc.)  So 
increasing the -ad to 8192 seems to be prohibitively expensive at this 
point.

Thanks.