Returns the length of the curve's segment between the curve's start point and the specified point
Supported Platforms: Windows only
(vlax-curve-getDistAtPoint curve-obj point)
Type: VLA-object
The object to be measured.
Type: List
A 3D point list (in WCS) on curve-obj.
Type: Real or nil
A number if successful; otherwise nil.
Set OSNAP to tangent and select the point where the line is tangent to the curve:
(setq selPt (getpoint)) (4.91438 6.04738 0.0)
Determine the distance from the start of the curve to the selected point:
(vlax-curve-getDistAtPoint splineObj selpt) 5.17769