Create a line from a point to the perpendicular projection of that point onto a curve.

Input parameters:

1. Pt → Line start point.
2. Cr → Curve for perpendicular constraint.
3. Lc → Optional cue for perpendicular location.

Output parameters:

1. Ln → Line perpendicular to and coincident with the curve.
2. Lc → Curve locus at perpendicular line end point.