Create a circle whose radius lies within the curved space of a sphere's outer surface.

Input parameters:

1. Sp → Constraining sphere.
2. XY → Circle centre as a longitude angle in spherical coordinates.
3. Z → Circle centre as a latitude angle in spherical coordinates.
4. Rd → Radius of circle as measured within the sphere outer surface.

Output parameters:

1. Ci → Circle coincident with the sphere surface.