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

[Andrew McNeil]

One more thing, the patch numbers will be different for incident and
exiting hemispheres.  one side uses left handed numbering the other uses
right handed numbering.  Energy that is transmitted specularly will have
the same incident and exiting patch number.

Andy

On Mon, Oct 22, 2012 at 9:45 AM, Andrew McNeil <amcneil at lbl.gov> wrote:

> Jia,
> This diagram: https://dl.dropbox.com/u/15562376/bin.jpg is wrong.
> You should look at klems_int.cal to determine what the patch numbers are.
>  My bad.
> Andy
>
> On Sat, Oct 20, 2012 at 5:11 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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>>
>>
>
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