确定3点的时针方向

marting

1. ;; Clockwise-p  -  Lee Mac
   
2. ;; Returns T if p1,p2,p3 are clockwise oriented
   
3. 
   
4. (defun LM:clockwise-p ( p1 p2 p3 )
   
5.     (<  (* (- (car  p2) (car  p1)) (- (cadr p3) (cadr p1)))
   
6.         (* (- (cadr p2) (cadr p1)) (- (car  p3) (car  p1)))
   
7.     )
   
8. )
   

;; Clockwise-p  -  Lee Mac<br /> ;; Returns T if p1,p2,p3 are clockwise oriented<br /> <br /> (defun LM:clockwise-p ( p1 p2 p3 )<br />     (<  (* (- (car  p2) (car  p1)) (- (cadr p3) (cadr p1)))<br />         (* (- (cadr p2) (cadr p1)) (- (car  p3) (car  p1)))<br />     )<br /> )<br />