[Radiance-general] front and back transmission in BSDF

[Jia Hu]

Hello:

What is the definition of "front" and "back" transmission in the BSDF xml
file? I  test using BSDF files of Window 6 and genBSDF,  and find that it
uses "Transmission Back" to calculate radiance. "genBSDF +forward -backward
test.rad > test.xml" gave zero illuminance.  So "back"  denotes from
outside to inside (towards inside the room)?  that is, the incident ray
falls on the outside window surface?

However, the three-phase daylight coefficient method  tutorial mentions
that Radiance uses "front transmission" data. In addition, in source code:
bsdf.c, line 1343:

                    # line 1343
if (!strcasecmp(ezxml_txt(ezxml_child(wdb,
"WavelengthDataDirection")),
"Transmission Front"))
break;

It looks using "transmission front".

Which (front or back) transmission does Radiance use?

Thanks,

Jia
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