Returns the point (in WCS) on a curve that is nearest to the specified point
(vlax-curve-getClosestPointTo curve-obj givenPnt [extend])
Arguments
The VLA-object to be measured.
A point (in WCS) for which to find the nearest point on the curve.
If specified and not nil, vlax-curve-getClosestPointTo extends the curve when searching for the nearest point.
Return Values
A 3D point list representing a point on the curve, if successful; otherwise nil.
Examples
Assume that the curve being measured is the arc in the following drawing:

Return the closest point on the arc to the coordinates 6.0, 0.5:
(vlax-curve-getClosestPointTo arcObj '(6.0 0.5 0.0)) (6.0 1.5 0.0)
Return the closest point on the arc to the coordinates 6.0, 0.5, after extending the arc:
(vlax-curve-getClosestPointTo arcObj '(6.0 0.5 0.0) T) (5.7092 0.681753 0.0)