Rendering falsecolor on glass with vwrays

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

The first rtrace computes the intersection point (which is fast) and the second rtrace does the illuminance
calculation. Cool, yes? Yes.