[Radiance-general] Progress Report

[Rob Guglielmetti]

Well, I don't know that I'm as close as I'd like to be, but I am getting 
better results now, even with the denser shades.

In short, what I did was roll all the suggestions into a new set of 
simulations.  Specifically, I added:

render= -lw 1e-8 -av 0 0 0

... to my rif file, increased the ambient bounces to five, and 
normalized all my shade relfectances (20%).  Here's what I got:

Test20 (no shade)		82,356	249.82			
Test21 (10% shade)		82,350	30.89	10.00%	12.36%	24%
Test22 (05% shade)		82,343	16.32	5.00%	6.53%	31%
Test23 (01% shade)		82,346	1.38	1.00%	0.55%	-45%
Test24 (10% + 05% shades)	82,338	0.80	0.50%	0.32%	-36%
Test25 (10% + 01% shades)	82,354	0.35	0.10%	0.14%	40%
Test26 (01% + 01% shades)	82,348	0.01	0.01%	0.00%	-60%

Data is as follows:
Column 1 - Exterior horizontal diffuse illuminance (Lux)
Column 2 - Interior horizontal diffuse illuminance (Lux)
Column 3 - "expected" light reduction from test 20 (no shade)
Column 4 - actual light reduction from test 20 (no shade)
Column 5 - "error".  I'm certainly no statistician though, and maybe 
this value is being unfairly computed (COL4/COL3)-1.  (?)

As you can see, there is still some wild fluctuation, but not nearly as 
bad as the original tests.  I am confused as to why the accuracy of the 
10% and 05% shades has suffered; in earlier tests they were very close, 
04% and 08% "accurate" respectively.

OK, so then I tried Alex's trick of increasing the exterior illumination 
  by a factor of ten, in hopes that the higher light levels that would 
now result in the interior space would be more accurately evaluated:

(HDI x 10)
Test20 (no shade)		832,317	2,528.67			
Test21 (10% shade)		832,319	361.96	10.00%	14.31%	43%
Test22 (05% shade)		832,322	222.05	5.00%	8.78%	76%
Test23 (01% shade)		832,315	23.48	1.00%	0.93%	-7%
Test24 (10% + 05% shades)	832,297	17.45	0.50%	0.69%	38%
Test25 (10% + 01% shades)	832,314	2.98	0.10%	0.12%	18%
Test26 (01% + 01% shades)	832,304	0.37	0.01%	0.01%	46%

~8-/

Now my 05% shade is the least accurate of the lot!  I double checked the 
paramaters, and even re-ran the calc using five points in an array 
around the intitial calc point, but it averages to within .5 lux of this 
calc.  I did a rendering of the 05% shade too, everything looks OK.

Hmmm. Even at these higher light levels, the 01% + 01% shade seems 
suspect.  This combo had the greatest "swing" from the first simulation 
to the second (60% under-prediction to a 46% over prediction).

My co-worker & I have been thinking that maybe we should test the model 
with more transmissive shades, and simply apply a factor to those 
illuminance values to figure out what the shades should be, for this 
last gallery.  It feels a lot like giving up, but I'm not sure I want to 
trust these numbers based on this test.

Either way we go, this has been very educational and I thank everyone 
who contributed to this thread.

-- OK, seconds before I was to press send, Carsten Bauer sent me an 
email.  He's been doing some testing of his own with this model, with 
much better results.  It seems that if we set -lw to zero, and not a 
really-really low number, you get results that match the math.  The 
other big difference between his process and mine is that he's getting 
his values from a rendering (rpict) and I'm just rtracing values.  So 
perhaps there's the missing link(s).

Maybe I won't give up just yet...  Seems like there's just no way to 
know all there is to know about Radiance!

To be continued (?)

----

      Rob Guglielmetti

e. rpg@rumblestrip.org
w. www.rumblestrip.org