[Radiance-general] rewrite BRDF as .cal file for plasfunc

[Katja Doerschner]

Hi Roland,
I just tried out your suggestion after getting funny results with the
DxDyDz as view direction. Your 'hack' works perfectly!!!!! Thanks a lot.

katja 

----- Original Message -----
From: Roland William Fleming <roland.fleming at tuebingen.mpg.de>
Date: Monday, July 18, 2005 11:44 am
Subject: Re: [Radiance-general] rewrite BRDF as .cal file for plasfunc

> 
> Hi Katja ---
> 
> Here's the hack I use.  Pass the viewpoint as arguments to the .cal 
> function.  Then view direction is just:
> 
> Vx = -(arg(1) - Px);
> Vy = -(arg(2) - Py);
> Vz = -(arg(3) - Pz);
> 
> where Px, Py and Pz are the Radiance predefined variable names for 
> the 
> ray intersection points.
> 
> Hope this helps,
> Roland
> 
> 
> On Jul 18, 2005, at 5:26 PM, Katja Doerschner wrote:
> 
> > I sent this message earlier - but I think it may have gotten 
> lost. I
> > apologize if you receive it twice!
> >
> > Hello,
> >
> > Has anyone an example of how to write a .cal function for plasfunc,
> > for a given BRDF?
> > Specifically, I am not sure which predefined variables correspond to
> > the view direction vector.
> >
> > This is the BRDF I want to use in Radiance:
> > V(i,j,n,a)=(1/PI)*(a/(a+(i dot n)(j dot n))
> > :i is unit vector from the source direction, j is unit vector of 
> view> direction, n is surface normal, a some other parameter.
> >
> > I know the Radiance-predefined variable names for the source 
> direction> (x,y,z) and surface normal (Nx,Ny,Nz), but I am not sure 
> what to use
> > for the view direction.
> >
> > Can anyone help?
> > Thank you!
> > katja
> >
> >
> >
> >
> > _______________________________________________
> > Radiance-general mailing list
> > Radiance-general at radiance-online.org
> > http://www.radiance-online.org/mailman/listinfo/radiance-general
> >
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