The Surface Parameters option creates a curve that follows the parametric path of a selected spline surface.
Isocurve Methods
Select from three methods to create the curve.
Direction on Surface
Select two points to indicate the isoparametric curve used to define the new curve.
Point on Edges
Select a location on the surface edge to create a curve passing through that location, normal to the edge. You can select any UV parameters, that is, any surface location, but it will automatically use the nearest edge (minimum parametrical distance) from the selected location. You can alternatively select an existing point on the edge. A green line will be displayed to indicate the normal direction from the selected edge.
By Parameter
Select either the U or V direction and the parameter value between 0 and 1 to create an isoparametric curve.
Note: If the UV boundary curve data is corrupted, then the following error message may appear: "No active isocurve segments found for this parameter." Use the Geometry > Repair Geometry > Build Topology function to resolve any gaps in the boundary curves.