[Radiance-general] Angular selectivity of blinds

[Greg Ward]

It means that the .cal file assumes the surface is aligned in the x-y 
plane.  Assuming you want a vertical grid and your z-axis is up, adding 
the following transform to the string arguments would rotate the 
material so that your surface was instead in the x-z plane:

	-rx -90

Since we use a right-handed coordinate system in Radiance, and positive 
angles correspond to counter-clockwise rotations looking down the 
selected axis, this rotates the positive y direction in the original 
orientation so it is now in the positive z direction.  Since this 
material is symmetric front-to-back, it actually didn't matter in this 
case which direction we rotated it.

If you want the surface in the y-z plane instead,  you would use:

	-ry -90

This rotates the positive x-axis into the positive z direction.  Just 
to be clear, your BRTDfunc would look like so:

void BRTDfunc grating
12
         0       0       0
         spectrans spectrans spectrans
         0       0       0
         grating.cal -ry -90
0
13
         rrefl grefl brefl
         rtrns gtrns btrns
         rrefl grefl brefl
         A10 A11 A12 A13

You just add a couple of arguments to the string arg count, and tack 
them on the end.

I hope this helps.
-Greg

> From: Richard Clibborn <furry at ihug.com.au>
> Date: February 15, 2005 10:07:55 PM PST
>
> Greg,
>
> Thanks for that.  I'm just a little unsure about the orientation of
> this "aligned with x-y plane" in the header .. is this absolute (ie. 
> the
> project x-y plane) or does it automatically align with the surface it 
> is being
> applied to.  Sorry if this is a stupid question, it's just I have had 
> trouble
> before simulating fritting with mixfunc and different surface 
> orientations.
>
> Cheer,
> Richard.