;; | ----------------------------------------------------------------------------
;; | GE_PerpPt
;; | ----------------------------------------------------------------------------
;; | Function : Locate the perpendicular drop point from a point pp to any line
;; |            segment defined by two other points pt1 and pt2
;; | Argument : [pp]  - Point to drop from
;; |            [p1] - First Point of line segment
;; |            [p2] - Second Point of line segment
;; | Return   : The drop point on the line segment
;; | e-mail   : rakesh.rao@4d-technologies.com
;; | Web      : www.4d-technologies.com
;; | ----------------------------------------------------------------------------


(defun GE_PerpPt( pp p1 p2 / x y x1 x2 x3 x4 y1 y2 y3 y4 m p4)

(setq
	x (car pp)
	y (cadr pp)
	x1 (car p1)
	y1 (cadr p1)
	x2 (car p2)
	y2 (cadr p2)
)

(cond
	((equal x1 x2 0.0000001)		; Vertical line
		(setq
			x4 x1
			y4 y
			p4 (list x4 y4 0.0)
		)
	)
	((equal y1 y2 0.0000001)		; Horizontal line
		(setq
			x4 x
			y4 y1
			p4 (list x4 y4 0.0)
		)
	)
	(T
		(setq
			m (/ (- y2 y1) (- x2 x1))		; gradient p1- p2
			x4 (/ (+ (/ x m) (+ y (- (* m x1) y1))) (+ (/ 1 m) m))
			y4 (+ y1 (* m (- x4 x1)))
			p4 (list x4 y4 0.0)
		)
	)
)
p4
)