[Radiance-general] Illuminance calculation on a virtual surface?

[Jim Estes]

Rob Guglielmetti wrote:
> Hi Greg, Hi John,
> 
> Greg Ward wrote:
> 
>> No good.  Trans gets ignored by the rpict -i option.  Just use pfilt 
>> to scale the illuminance map if it's not big enough.  (John M's 
>> suggestion -- he's sitting next to me in Leicester.)

Thanks, that should get me there. Also thanks to Raphael for pointing out
the obvious that I missed in the rtrace man page for computing an image
(using the "-fac -x and -y" options, so far it is generating bad picture
files, but I'm on the right track).

> vwrays -x XRES -y YRES -vf viewfile -fd | rtrace -h -fd -opn octree \
> | rtrace -fdc -I render_options -x XRES -y YRES octree > illum_picture.pic
> 
> Greg, does this look familiar?  A little ditty from a year or so ago? 
> You sent me this tip when I asked you how to get illuminance on a 
> building's curtain wall.  The first rtrace computes the intersection 
> point (which is fast) and the second rtrace does the illuminance 
> calculation.  Cool, yes?  Yes.
> 
> Now, given this little tip, could he use trans as I described?

Thanks. That looks promising. My next step was to create a finer grid for
input to rtrace anyway. If this technique works not only would it do that
but hopefully (maybe) render the image much faster also. It might take a
little while but if I come up with anything interesting I'll report back.

Jim Estes