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

[Andrew McNeil]

dctimestep originally used just the front transmission data, and if front
transmission data were missing the result was zero.  I think Greg has
recently made changes so that it can us back transmission too.  Try with
the HEAD.

Andy


On Sat, Oct 20, 2012 at 5:38 PM, Jia Hu <hujia06 at gmail.com> wrote:

> 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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