[Radiance-general] possible inconsistency of bin numbers between BSDF and kelms_int.cal

[Jia Hu]

Sorry to keep bothering you...  Just add some additional information. I
search "transmission back" and "transmission front" in the code and find
"Transmission Front" is more likely used according to the code.  The
following two code snippets from bsdf_m.c and bsdf.c shows "Transmission
Front" data will be loaded or preferred ?

Another issue,  I remember Greg mention that even if only "Transmission
Front" is present, the BSDF library in Radiance can still computer
Transmission matrix. But my simple test case (download
here<https://dl.dropbox.com/u/15562376/test_10_21.zip>)
did not show that.  If you change "Transmission Back" in the .xml file to
"Transmission Front". The results will be zero.


*//  ray/src/common/bsdf_m.c*
/*
 * Remember that front and back are reversed from WINDOW 6 orientations
 * *Favor their "Front" (incoming light) since that's more often valid*
 */
 tfront = !strcasecmp(sdata, "Transmission Back");
if (!strcasecmp(sdata, "Transmission Front") ||
 tfront & (sd->tf == NULL)) {
if (sd->tf != NULL)
SDfreeSpectralDF(sd->tf);
 if ((sd->tf = SDnewSpectralDF(1)) == NULL)
return RC_MEMERR;
df = sd->tf;

*// ray/src/common/bsdf.c*

for (wld = ezxml_child(wtl, "WavelengthData");
wld != NULL; wld = wld->next) {
 if (strcasecmp(ezxml_txt(ezxml_child(wld,"Wavelength")),
"Visible"))
 continue;
for (wdb = ezxml_child(wld, "WavelengthDataBlock");
 wdb != NULL; wdb = wdb->next)
if (!strcasecmp(ezxml_txt(ezxml_child(wdb,
 "WavelengthDataDirection")),
*"Transmission Front"))*
 break;
if (wdb != NULL) { */* load front BTDF */*
 load_bsdf_data(dp, wdb);
break; /* ignore the rest */
 }
}

Thanks,

Jia

On Sat, Oct 20, 2012 at 4:01 PM, Jia Hu <hujia06 at gmail.com> wrote:

> Hi all:
>
> In the Klems_init.cal file, for south window (using kbinS), the Klems
> coordinate is defined as:
>
> z+: pointing to inside (that is, (0,1, 0)  )
> x+: pointing to West ( that is (-1, 0, 0) )
> y+: pointing to Up (0,0,1)
>
> This coordinate is consistent with the Klems coordinate system used in
> WINDOW 6 (see this: https://dl.dropbox.com/u/15562376/coordinate.jpg). In
> the figure, Klems coordinate system defines: x or xr points to (-1, 0, 0)
> and  y or yr points to (0, 0, 1).
>
> However, if using this command to calculate view matrix:
>
> $ rtcontrib < test.pts -f klems_int.cal -bn Nkbins -b *kbinS* -bn Nkbins
> -m window_mat -I+ -ab 3 -ad 2000 -lw 1e-4 interior.oct > south.vmx
>
> where, kbinS defines z axis in the Klems coordinate system as (0 1 0),
> that is, pointing to room interior.
>
> Thus, the bin number calculated by Klems_init.cal is actually based on z
> hemisphere <https://dl.dropbox.com/u/15562376/coordinate.jpg> (the
> hemisphere protrudes towards room). the bin number corresponds with
> "Transmittance Front" in BSDF xml file. For example, ray direction (-1, -1,
> 0) (backward, ray travels from inside to outside room) hits the bin 58<https://dl.dropbox.com/u/15562376/bin.jpg>
> defined in z hemisphere because the hemisphere protrudes towards (0 1 0).
>  But ray direction (-1 -1 0) hits bin 46<https://dl.dropbox.com/u/15562376/bin.jpg> defined in
> z reverse (i.e., zr) coordinate because the hemisphere protrudes towards (0
> -1 0) (towards outside).
>
> When calculating Daylighting Matrix, it still uses Klems_init.cal and
> kbinS, that is, z hemisphere coordinate system, therefore, Radiance seems
> needing to use "Transmission Front", which is defined in z hemisphere.  But
> currently Radiance uses "Transmission Back" (from inside to outside), which
> defined in zr hemisphere,
>
> So, should we need to
>
>  (a) use "*kbinN*" (defining z axis of Klems coordinate towards (0 -1 0)
> )  and "Transmission Back" for south window,  or
>   (b) use "Transmission Front" and *kbinS*?
>
>  I am very confused about this. Does anyone know the possible reasons?
>
> Thank you !
>
> Jia
>
>
> On Sat, Oct 20, 2012 at 8:11 AM, Jia Hu <hujia06 at gmail.com> wrote:
>
>> Hi all:
>>
>> I have a question about the bin number.
>>
>> To calculate view matrix:  (south-facing window)
>> $ rtcontrib < test.pts -f klems_int.cal -bn Nkbins -b kbinS -bn Nkbins -m
>> window_mat -I+ -ab 3 -ad 2000 -lw 1e-4 interior.oct > south.vmx
>>
>> kbinS uses the (0, 1, 0) as normal (pointing to inside room).
>>
>> For a ray direction (-1, -1, 0), using klems_int.cal to calculate the bin
>> number, the bin number is about #57 (I did it manually).
>>
>> Klems_int.cal (download Klems_init.cal<https://dl.dropbox.com/u/15562376/klems_int.cal>)
>> seems use "z" hemisphere (see this figure:
>> https://dl.dropbox.com/u/15562376/coordinate.jpg). From the figure, we
>> can see "z" hemisphere points to the room (that is, the hemisphere is
>> located in the room) "zr" (z reverse) hemisphere is towards outside (the
>> hemisphere is outside the room).
>>
>> The possible inconsistency is:
>>
>> (1) Klems_int.cal uses "z" hemisphere to calculate the bin number, for
>> example,  for ray direction (-1, -1, 0), the bin number is #57 for "z"
>> hemisphere coordinate. (see this figure:
>> https://dl.dropbox.com/u/15562376/bin.jpg)
>>
>> (2) The "Transmission Back" data in the BSDF .XML is used in the three
>> phase DC method (see Greg's explanation<http://permalink.gmane.org/gmane.comp.graphics.radiance.general/2729>),
>> and thus the calculation is based on "zr" (z reverse) hemisphere , for ray
>> direction (-1, -1, 0), the bin number is about #69 according to the "z
>> reverse" hemisphere coordinate (see this figure:
>> https://dl.dropbox.com/u/15562376/bin.jpg).
>>
>> So my questions are:
>>
>> (a) Given the ray direction, which hemisphere ( "z" or "zr" ) does
>>  "Klems_init.cal" use?
>>
>> (b) whether the bin numbers (for the same ray direction) between
>> "Klems_int.cal" and BSDF .xml  are inconsistent or not?
>>
>> (c) if they are using different bin numbers, how to handle ViewMatrix *
>> BSDF in the calculation?
>>
>> Thank you in advance,
>>
>> Jia
>>
>
>
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