Compute an isovist by casting sample rays spherically around a location.

Input parameters:

1. Pl → Sampling plane and origin. For a hemisphere the plane is the horizon and rays are cast above it.
2. Cn → Number of sample rays.
3. Rd → Sample radius.
4. Ob → Obstacles to sample against (curves, planes, surfaces, breps and meshes are supported).
5. Dm → Whether to sample the upper hemisphere or the full sphere of directions.
   • 0 → Hemisphere
   • 1 → Sphere
6. 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 intersection 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.