[Radiance-general] cross check with rcontrib -V+ -I

[Mario Geiger]

Hi

I did a simple test to know if I understood correctly what "rcontrib -V+
-I" computes.

I created a scene with a light, the shape of a ring of radius *r*.
void light windowglow 0 0 3 1 1 1
windowglow ring window_0
0 0 8
0 0 0
0 1 0
0 *r*

oconv scene.rad > scene.oct

And I run the following command :
echo 0 *y* 0   0 -1 0 | rcontrib -V+ -I -st 0.15 -dj 0.7 -ds 0.15 -dt 0.05
-dc 0.5 -dr 3 -dp 512 -ab 2 -ad 4096 -ar 128 -aa 0.15 -av 0 0 0 -as 1024
-lw 1e-9 -m windowglow -n 4 scene.oct

By hand I computed that the resulting coefficient to transform the constant
radiance of the source (1 W/m2/sr) to the irradiance at the point (looking
towards the source) should be *pi * sin(a).^2* where *a = atan(r/y)*

So I do a variation of the angle *a*. I keep *y* constant (10m) and I get
this results for 2000 points.

What is wrong with the simulation or my calculus ? Why do the points spread
out at large angle ? Why do  the coefficients becomes small at very large
angle ? Does the source follow the Lambert's cosine law ?

Thanks in advance,

Sorry for my english,

Mario Geiger
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