[Radiance-general] Query regarding rcontrib

[Axel Jacobs]

Hi Don,

> Two things:
> 1 - You should use the same material for the sky and ground so that the
> ground reflected component is included in patch 0. I typically use a single
> 360 degree source to encompass by sky and ground.

I completely agree with Andy. Put this in your white_sky.sky:
void glow sky_glow
0
0
4  1 1 1  0

sky_glow source sky
0
0
4  0 0 1  360

> 2 - Your zip file didn't include test_Model1.opt, used by the rcontrib
> command, but make sure that -ab is 2 or greater to
> get inter-reflected contribution from the sky on a ceiling illuminance
> sensor (if -ab isn't sepcified in the opt file rcontrib defaults to -ab 1).

@Andy
The file names are all messed up by Windows. It's test_Model2.opt that 
you're looking for. -ab is actually set to 5.

@Don,
you're overwriting rcontrib's default for -lr:
$ rcontrib -defaults
...
-lr -10     # limit reflection (Russian roulette)
...

Your setting it to -lr 8
Note the difference between positive and negative integers. I have to 
admit that this is one of the more obscure options that I don't tend to 
temper with. See man rpict. I ran your model with the -lr 8 removed from 
the opt file. Completely different outcome.

Also, your -ad is not very high. Unless you nudge it up a lot, there is 
no point in using 4 Reinhart subdivisions of the Tregenza patches. An 
-ad of 4096 is decent for a normal rtrace daylight simulation. For 
rcontrib, it should be much higher.

I don't know how you post-process the irradiance vector, since this 
script(?) is not included in the Zip file. However, you're calling 
rcontrib with the -V+ option. This gives you the *absolute* contribution 
from the sky patches, ie the irradiance at the sensor points.

One tends to use -V- here to get the daylight coefficients, ie the 
*relative* contribution from the sky patches. Once they have been 
calculated, the DC are multiplied with the sky vector to get actual 
irradiance values.

Regards

Axel