[Radiance-general] Questions about local coordinate systems
Peter Apian-Bennewitz
[email protected]
Thu, 27 Sep 2001 10:29:11 +0200
--------------0A8C9707367113C067557EF7
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
[email protected] wrote:
> Hi!
>
> I am using the transdata material for incorporating BTDF's in
> Radiance. In this context, I have to convert cartesian coordinates in
> polar coordinates.
> For a surface (i.e. rectangle) the normal is determined by the right-
> hand rule. So far - so good. Unfortunately, I am not sure how the
> local coordinate system for the rectangle is defined?! How are the x-
> axis, y-axis and z-axis are oriented? The source ray direction
> (x,y,z) and the transmitted ray direction (Dx,Dy,Dz) are referring to
> this local coordinate system, aren't they?
no- All coordinates refer to world coordinates. Radiance doesn't
support a local coordinate attached to the primitive. If you want one,
you have a calculate it manually using the surface normal and a
reference axis and do some vector crosspoducts.
Other programs (e.g. Rayshade) supply a default local coordinate system,
I guess Greg hasn't build one into it since it's not clear what
'default'
means: For one large polygon it *might* seem obvious, for a tesselated
surface it would be not.
-Peter
>
>
> Could anybody give a hint to solve my problems?
>
> Best regards,
>
> Frank
>
> _______________________________________________
> Radiance-general mailing list
> [email protected]
> http://www.radiance-online.org/mailman/listinfo/radiance-general
--
pab-opto, Freiburg, Germany, www.pab-opto.de
--------------0A8C9707367113C067557EF7
Content-Type: text/html; charset=us-ascii
Content-Transfer-Encoding: 7bit
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
[email protected] wrote:
<blockquote TYPE=CITE>Hi!
<p>I am using the transdata material for incorporating BTDF's in
<br>Radiance. In this context, I have to convert cartesian coordinates
in
<br>polar coordinates.
<br>For a surface (i.e. rectangle) the normal is determined by the right-
<br>hand rule. So far - so good. Unfortunately, I am not sure how the
<br>local coordinate system for the rectangle is defined?! How are the
x-
<br>axis, y-axis and z-axis are oriented? The source ray direction
<br>(x,y,z) and the transmitted ray direction (Dx,Dy,Dz) are referring
to
<br>this local coordinate system, aren't they?</blockquote>
no- All coordinates refer to world coordinates. Radiance doesn't
<br>support a local coordinate attached to the primitive. If you want one,
<br>you have a calculate it manually using the surface normal and a
<br>reference axis and do some vector crosspoducts.
<br>Other programs (e.g. Rayshade) supply a default local coordinate system,
<br>I guess Greg hasn't build one into it since it's not clear what
'default'
<br>means: For one large polygon it *might* seem obvious, for a tesselated
<br>surface it would be not.
<p>-Peter
<blockquote TYPE=CITE>
<p>Could anybody give a hint to solve my problems?
<p>Best regards,
<p>Frank
<p>_______________________________________________
<br>Radiance-general mailing list
<br>[email protected]
<br><a href="http://www.radiance-online.org/mailman/listinfo/radiance-general">http://www.radiance-online.org/mailman/listinfo/radiance-general</a></blockquote>
<pre>--
pab-opto, Freiburg, Germany, www.pab-opto.de</pre>
</html>
--------------0A8C9707367113C067557EF7--