;; | ----------------------------------------------------------------------------
;; | MI_InterP
;; | ----------------------------------------------------------------------------
;; | Function : Interpolate Z value between two points
;; | Auguments: 'pt'  - The 2D point at which Z is required
;; |            'pt1' - First point for interpolation
;; |            'pt2' - Second point for interpolation
;; | Return   : The interpolated 3D point
;; | Updated  : April 22, 1998
;; | e-mail   : rakesh.rao@4d-technologies.com 
;; | Web      : www.4d-technologies.com
;; | ----------------------------------------------------------------------------


(defun MI_InterP(pt pt1 pt2 / Z1 Z2 Z hlen1 hlen2)

(setq
	hlen1 (distance
				(list (car pt1) (cadr pt1) 0.0)
				(list (car pt2) (cadr pt2) 0.0)
			)
	hlen2 (distance
				(list (car pt) (cadr pt) 0.0)
				(list (car pt1) (cadr pt1) 0.0)
			)
	Z1 (caddr pt1)
	Z2 (caddr pt2)
)

(if (not (zerop hlen1))
	(setq Z (+ Z1 (/ (* hlen2 (- Z2 Z1)) hlen1)))
	(setq Z (* 0.5 (+ Z1 Z2)))
)

(list (car pt) (cadr pt) Z)
)