Compute a single isovist sample by casting one ray into a collection of obstacles.

Input parameters:

1. Sm → Sampling ray. Its start is the origin and its direction the cast direction.
2. Rd → Sample radius.
3. Ob → Obstacles to sample against (curves, planes, surfaces, breps and meshes are supported).
4. 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 the sample ray stops, either at an intersection or at the horizon.
2. Ry → Ray vector from the origin to the sample point.
3. Ds → Distance from the origin to the sample point.
4. Ix → Index of the obstacle hit, or -1 if no obstacle was hit.