strange rfluxmtx behavior

Dear Radiance mailing list,

it seems to me that the following sentence of the rfluxmtx man page is not correct:
“Rays always emanate from the back side of the sender surface and arrive at the front side of receiver surfaces.”

Unfortunately, the direction of the receiver surface doesn’t seem to influence the result:

$ cat surface_0.rad

#@rfluxmtx h=u
surf_mat_0 polygon surface_0.5137
0
0
12
3.9 0 0
3.9 8.5 0
3.9 8.5 3.1
3.9 0 3.1

$ cat surface_0_turned.rad

#@rfluxmtx h=u
surf_mat_0 polygon surface_0.5137
0
0
12
3.9 0 0
3.9 0 3.1
3.9 8.5 3.1
3.9 8.5 0

$ cat surface_3.rad

#@rfluxmtx h=u
surf_mat_3 polygon surface_3.1540
0
0
12
0 8.5 0
0 8.5 3.1
3.9 8.5 3.1
3.9 8.5 0

$ cat room.mat

void plastic surf_mat_0
0
0
5 0.200 0.200 0.200 0 0

void plastic surf_mat_3
0
0
5 0.500 0.500 0.500 0 0

$ rfluxmtx -h surface_0.rad surface_3.rad -w room.mat
rcontrib: warning - no light sources found
9.740000e-02 9.740000e-02 9.740000e-02

$ rfluxmtx -h surface_3.rad surface_0.rad -w room.mat
rcontrib: warning - no light sources found
2.154000e-01 2.154000e-01 2.154000e-01

$ rfluxmtx -h surface_0_turned.rad surface_3.rad -w room.mat
rcontrib: warning - no light sources found
0.000000e+00 0.000000e+00 0.000000e+00

$ rfluxmtx -h surface_3.rad surface_0_turned.rad -w room.mat
rcontrib: warning - no light sources found
2.154000e-01 2.154000e-01 2.154000e-01

Has this behavior been chosen on purpose? What am I doing wrong? In my opinion, the two commands

$ rfluxmtx -h surface_3.rad surface_0.rad -w room.mat
$ rfluxmtx -h surface_3.rad surface_0_turned.rad -w room.mat

should have different results.

Thank you for your help!!
Regards,
Wendelin

By the way: thank you Greg for rfluxmtx! It simplifies the rcontrib procedure significantly.

···

Dr. Wendelin Sprenger
Division Thermal Systems and Buildings
Fraunhofer Institute for Solar Energy Systems ISE
Heidenhofstr. 2, 79110 Freiburg, Germany
Phone: +49 (0) 7 61/ 45 88-57 45
[email protected]
http://www.ise.fraunhofer.de

Hi Wendelin,

There should probably be a clarification in the man page regarding uniform sampling, which currently ignores the surface orientation. I don't know whether it would be better to document this in the man page or change the code so that back of uniform receivers do not accumulate energy. Is this important in your application?

Cheers,
-Greg

···

From: [email protected]
Date: January 29, 2015 8:10:05 AM PST

Dear Radiance mailing list,

it seems to me that the following sentence of the rfluxmtx man page is not correct:
"Rays always emanate from the back side of the sender surface and arrive at the front side of receiver surfaces."

Unfortunately, the direction of the receiver surface doesn't seem to influence the result:

$ cat surface_0.rad

#@rfluxmtx h=u
surf_mat_0 polygon surface_0.5137
0
0
12
                3.9 0 0
                3.9 8.5 0
                3.9 8.5 3.1
                3.9 0 3.1

$ cat surface_0_turned.rad

#@rfluxmtx h=u
surf_mat_0 polygon surface_0.5137
0
0
12
                3.9 0 0
                3.9 0 3.1
                3.9 8.5 3.1
                3.9 8.5 0

$ cat surface_3.rad

#@rfluxmtx h=u
surf_mat_3 polygon surface_3.1540
0
0
12
                  0 8.5 0
                  0 8.5 3.1
                3.9 8.5 3.1
                3.9 8.5 0

$ cat room.mat

void plastic surf_mat_0
0
0
5 0.200 0.200 0.200 0 0

void plastic surf_mat_3
0
0
5 0.500 0.500 0.500 0 0

$ rfluxmtx -h surface_0.rad surface_3.rad -w room.mat
rcontrib: warning - no light sources found
9.740000e-02 9.740000e-02 9.740000e-02

$ rfluxmtx -h surface_3.rad surface_0.rad -w room.mat
rcontrib: warning - no light sources found
2.154000e-01 2.154000e-01 2.154000e-01

$ rfluxmtx -h surface_0_turned.rad surface_3.rad -w room.mat
rcontrib: warning - no light sources found
0.000000e+00 0.000000e+00 0.000000e+00

$ rfluxmtx -h surface_3.rad surface_0_turned.rad -w room.mat
rcontrib: warning - no light sources found
2.154000e-01 2.154000e-01 2.154000e-01

Has this behavior been chosen on purpose? What am I doing wrong? In my opinion, the two commands

$ rfluxmtx -h surface_3.rad surface_0.rad -w room.mat
$ rfluxmtx -h surface_3.rad surface_0_turned.rad -w room.mat

should have different results.

Thank you for your help!!
Regards,
Wendelin

By the way: thank you Greg for rfluxmtx! It simplifies the rcontrib procedure significantly.

___________________________________
Dr. Wendelin Sprenger
Division Thermal Systems and Buildings
Fraunhofer Institute for Solar Energy Systems ISE
Heidenhofstr. 2, 79110 Freiburg, Germany
Phone: +49 (0) 7 61/ 45 88-57 45
[email protected]
http://www.ise.fraunhofer.de