求点到一条直线的垂足点

Public Shared Function GetFootOfPerpendicular(pt As XYZ, begin As XYZ, [end] As XYZ) As XYZ
	Dim dx As Double = begin.X - [end].X
	Dim dy As Double = begin.Y - [end].Y
	If Math.Abs(dx) < 1E-08 AndAlso Math.Abs(dy) < 1E-08 Then
		Return begin
	End If
	Dim u As Double = (pt.X - begin.X) * (begin.X - [end].X) + (pt.Y - begin.Y) * (begin.Y - [end].Y)
	u = u / ((dx * dx) + (dy * dy))
	'retVal.X = begin.X + u* dx;
	'   retVal.Y = begin.Y + u* dy;

	Dim retVal As New XYZ(begin.X + u * dx, begin.Y + u * dy, XYZ.BasisZ.Z)
	Return retVal
End Function