CurveClosestPoint Method 
Name  Description  

ClosestPoint(Point3d, Double) 
Finds parameter of the point on a curve that is closest to testPoint.
If the maximumDistance parameter is > 0, then only points whose distance
to the given point is <= maximumDistance will be returned. Using a
positive value of maximumDistance can substantially speed up the search.
 
ClosestPoint(Point3d, Double, Double) 
Finds the parameter of the point on a curve that is closest to testPoint.
If the maximumDistance parameter is > 0, then only points whose distance
to the given point is <= maximumDistance will be returned. Using a
positive value of maximumDistance can substantially speed up the search.
