How according to a point on the surface in the direction of length on the arc length point

Rhino Developer
1

How according to a point on the surface in the direction of length on the arc length point.
For example: in the V direction distance origin 10MM arc length on surface.

2

Extract an iso-curve on the surface at the point on the surface that runs in the V-direction. Then find the the length parameter for a length of 10 mm on that curve. Then use this parameter to evaluate the point on the iso curve.

In RhinoCommon you could use the Curve.LengthParameter method to find the desired parameter. http://4.rhino3d.com/5/rhinocommon/html/M_Rhino_Geometry_Curve_LengthParameter_1.htm