[Radiance-general] Illegal Power warning

[Greg Ward]

Hi Glen,

You need to pass the paramters given by BRTDfunc to its function  
calls explicitly.  The x, y, and z values are not defined globally.   
See the attached .cal file as a simple example of how this is done.

If your refllection color changes as a function of angle, you need to  
stick with the BRTDfunc type, as metfunc only offers a single color  
for highlights.  Keep in mind also that Radiance cannot calculate  
directional-diffuse components for anything other than highlights  
(i.e., light source reflections).  This is a limitation in Radiance's  
ability to sample BSDFs in general, and has been covered previously  
in numerous posts.

-Greg

-------------- next part --------------
A non-text attachment was scrubbed...
Name: tim1.cal
Type: application/octet-stream
Size: 692 bytes
Desc: not available
Url : http://radiance-online.org/pipermail/radiance-general/attachments/20071206/7def94d6/tim1.obj
-------------- next part --------------

> From: "G HARDING" <G.Harding1 at Bradford.ac.uk>
> Date: December 6, 2007 9:30:48 AM PST
>
> Hi Greg,
>
> I've attached the cal file.
> The file is for a particular measured surface (cardboard!), so it  
> doesn't
> use any input parameters.
>
> The idea behind the code is fairly simple (if executed rather  
> inelegantly!):
> Previous to the creation of this file, the reflectance of the  
> surface is
> measured over a range of angles, at several light source positions,  
> and a
> BRDF model (Lafortune) fitted to the data for each light position.
>
> The fitted parameters for the model at each light source position  
> are in the
> .cal file and it uses these (or interpolated values for intermediate
> angles), along with the light source and observation angles to  
> calculate the
> required reflectance via the model formulae.
>
> However, it doesn't work as I can't seem to get hold of the light  
> source
> vector, as mentioned in my previous email.
> Perhaps I'm going about this in completely the wrong way?
>
> I had considered using Metfunc rather than BRTDfunc (it would ne  
> nice to
> have the data in a separate file at least!), for which I've seen  
> examples
> which use the light source position data, but I need the colour to be
> specified by the data, not just the reflectance. I'm not sure if  
> this is
> possible with Metfunc?
>
> Many thanks for your time,
> Glen.
>
>
> -----Original Message-----
> From: Greg Ward [mailto:gward at lmi.net]
> Sent: 06 December 2007 16:43
>
> Hi Glen,
>
> I need a little more information -- can you send me your entire .cal
> file?
>
> Thanks,
> -Greg