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@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.vmxkbinS 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