SOS!如何判断多边形是否是自交的？

cadfqd

如何判断多边形是否是自交的？比如对顶角三角形的多边形；顶点走回头路的多边形等都属于自交的情况。怎样用lisp来快速的找出这样的多边形来并指出具体的自交位置？还望各位老师指点迷津．谢谢！

alin

Here is a routine from NG Autodesk, for closed LWPOLYLINE, you can use it. If it is not closed, close it first.

The error message, here is "Automation Error. Invalid input", might be different in Chinese version. You got to modify it.

;;f:pline_intersects returns T if given a self-intersecting lwpolyline

;;

(defun f:pline_intersects (en / sa rg)

(setq sa (vlax-make-safearray vlax-vbObject '(0 . 0))

sa (vlax-make-variant

(vlax-safearray-fill sa (list (f:enx en))))

) ;setq

(if (vl-catch-all-error-p

(setq rg (vl-catch-all-apply

'vla-addregion

(list (fx:active_space) sa))))

(if (wcmatch (vl-catch-all-error-message rg) "Automation Error. Invalid input")

;"*UNGÜLTIGE*")

T)

(vla-Delete

(car (vlax-safearray->list (vlax-variant-value rg))))

)

)

(defun fx:active_space ()

(if (zerop (getvar "TILEMODE"))

(vla-get-PaperSpace (fx:doc))

(vla-get-ModelSpace (fx:doc))

)

)

(defun f:enx (en)

(if (= (type en) 'ENAME)

(vlax-ename->vla-object en)

en

)

)

(defun fx:doc() (vla-get-activedocument (vlax-get-acad-object)))

龙龙仔

用intersectwith method 找(自身)交点,看顶点数与交点来判定是否自交(注意交点不包含首尾点)

无痕

楼上正解

alin

龙龙仔发表于2004-11-17 12:39:00用intersectwith method 找(自身)交点,看顶点数与交点来判定是否自交(注意交点不包含首尾点)

I'd like to know your completed answer.

龙龙仔

找(自身)交点= 求交点时选择同一条线试试

alin

问题是有时顶点重合

aeo000000

龙龙仔发表于2004-11-17 12:39:00用intersectwith method 找(自身)交点,看顶点数与交点来判定是否自交(注意交点不包含首尾点)

自相交，不一定有交点的（按楼主的意思，是走了回头路) 如果是回头的话，应该是去掉某一定义点，面积不会变。（以前想了很久的问题，答案不很全面，不过有些问题还是可以解决的)