Extract the surface isocurves coincident with a given locus. The isocurves will be limited to the interior of trimmed surfaces.

Input parameters:

1. Sf → Surface for isocurve extraction in the U and V directions.
2. Lc → Surface locus.

Output parameters:

1. Cu → Curve through the locus in the surface U direction.
2. Cv → Curve through the locus in the surface V direction.