Compute an isovist by casting sample rays radially around a plane.

Input parameters:

1. Pl → Plane encoding the location and orientation of the observer.
2. Cn → Number of isovist rays.
3. Rd → Optional maximum sampling radius. If omitted, the largest meaningful radius is picked and all hit-less rays are omitted from the outputs.
4. Ob → Ray obstacles. May incluce curves, planes, surfaces, and meshes.
5. Md → Ray casting accuracy. Accurate uses exact surface intersections; Fast meshes surfaces and breps for speed.
   • 0 → Accurate
   • 1 → Fast

Output parameters:

1. Pt → Point where each sample ray stops, either at an obstacle hit or at the horizon.
2. Ry → Ray vector from the origin to each sample point.
3. Ds → Distance from the origin to each sample point.
4. Ix → Index of the obstacle hit by each ray, or -1 if no obstacle was hit.