[Radiance-general] an invisible glow

[alex summerfield]

Hi

Does anyone have any suggestions for the following:

Under the current definition for glow

        mod glow id
        0
        0
        4 red green blue maxrad

if maxrad is a negative value, then the glow is visible on a surface but
does not participate in scene illumination.

I would like to generate a surface with a glow that does the opposite - from
the viewpoint invisible or assigned to another texture but as a glow it
still contributes to the indirect illuminance (in the same way that an illum
does with the direct calculation).

Is there a way to do this in general (with mixfunc?) so that a surface
appears from the viewpoint as one material, but as far as the lighting
calculation is concerned is another? Or more to the point how can i test if
the ray being traced is a view ray or not?

To explain an example situation - suppose there is a complicated existing
building that is simplest to represent with an image mapped onto its facade
(and that only appears correct when viewed from the viewpoint), but in terms
of its lighting contribution on the site in general is more accurately
described in some other way.

Any help is greatly appreciated.

Many thanks too to Peter, Greg, and the other regulars for their efforts in
revitalising the Radiance group.

cheers
alex

*******************************************************
A. J. Summerfield                 alex@arch.usyd.edu.au
Faculty of Architecture, University of Sydney
*******************************************************
Outside of a dog, a book is man's best friend.
Inside a dog, it's too dark to read.       Groucho Marx
*******************************************************