Create a pipe with a constant radius around a curve.

Input parameters:

1. Rl → Rail curve at the centre of the pipe.
2. Rd → Radius of pipe.
3. Ft → Fit a single surface to the rail curve.
   •  True → Fitted
   • False → Segmented
4. Cp → Pipe cap shape.
   • 0 → None
   • 1 → Flat
   • 2 → Round

Output parameters:

1. Pi → Pipe surface around rail curve.