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

[Andrew McNeil]

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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