Return the point whose distance from vertex 0 along the polyline is the
given fraction of the polyline's total length. Fractions less than zero
or greater than one are clamped. The return value is unit length. This
cost of this function is currently linear in the number of vertices.
The polyline must not be empty.
Return the point whose distance from vertex 0 along the polyline is the given fraction of the polyline's total length. Fractions less than zero or greater than one are clamped. The return value is unit length. This cost of this function is currently linear in the number of vertices. The polyline must not be empty.