[Radiance-general] lighting fixtures data

[Greg Ward]

Hi Will,

I don't really have time here to offer a complete tutorial on  
Radiance .cal files.  There's Chapter 4 of RwR and some useful  
information in <http://radsite.lbl.gov/radiance/refer/filefmts.pdf>.

Your results are actually OK.  If you reduce the exposure, you'll see  
that your source pattern is coming through.  The odd streaks at the  
edges are due to the fact that you have no cut-off in your fixture,  
but the distribution data is not quite zero at the edges.  Radiance  
is extrapolating the distribution function, which is a bad idea in  
this case.

-Greg

> From: william reynolds <william.reynolds at oriel.ox.ac.uk>
> Date: March 6, 2006 7:01:41 AM PST
>
> greg
> thanks for the suggestion for the mapping.
> i'm afraid i dont quite understand it though!
>
> i've put a rendering up at http://users.ox.ac.uk/~orie1226/rad/  
> again. its called lantern_2.2.pic (or .jpg) using your suggestions  
> for the .cal file. it seems to go a bit strange though, making a  
> sort of star pattern!
>
> the idea seems right - that the brightness of a ray is dependant on  
> the angle to the normal of the source (rather than on the point it  
> leaves the source from, as i originally had), but i'm lost with the  
> idea of a square picture covering 20 degrees! what does this mean?

It covers 20 degrees horizontally and vertically, and proportionally  
more than 20 degrees diagonally.

> please could you also explin the bit of code you gave? particularly  
> the divisor, and why there is an offset. also, what does the DEGREE  
> word do? i guess its a constant - perhaps to convert deg -> radians?

Actually, it's radiance -> degrees.

> thanks very much
> will
>