Don’t know if this needed a new topic as I touched this section of the cookbook in an old post concerning a different issue https://discourse.radiance-online.org/t/illuminance-values-contour-lines-on-a-working-plane/5167?u=danka
However, this is the procedure used:
$ vwrays -x 400 -y 400 -vf horizontal.vf
| rcalc -e '$1=$1;$2=$2;$3=.4;$4=$4;$5=$5;$6=1
| rtrace -fac -w -I -ov
vwrays -d -vf outside.vf \ -x 400 -y 400room.oct > wp_illu.hdr
I am not sure how in the Radiance cookbook the working plane is decided. Is the z coordinate of the camera (vp) the sets the height of the working plane, right? So vwrays would calculate all the values concerning the virtual horizontal plane that includes the vp. Would this be correct?