[求助]：已知仅有一段ARC的lwpolyline求圆心坐标？

nuance

怎样通过两端点坐标和弓弦比求圆心坐标？

hbshyjch

(defun c:12 ()
  (setvar "cmdecho" 0)
  (setq en (entsel "选取圆弧"))
  (setq en_data (entget (car en)))  ;提取群码
  (setq t1_list (cdr (assoc 10 en_data))) ;取得中点坐标  
  (princ "\n圆心坐标")
  (princ t1_list)
  (princ)
)
(princ "版本1.0 请键入12运行命令,该命令用于查询圆弧中心.")

不好意思没有弄清你的意思
看下面的帖子
http://www.mjtd.com/BBS/dispbbs. ... ID=42235&page=1

Underway

Ref link:
http://www.faqs.org/faqs/CAD/autolisp-faq/part2/section-6.html

;;; converts a bulged segment (bulge pt1 pt2) of a polyline
  ;;;   to a circle (ctr rad), the start- and endpoints are known
  ;;;   therefore the angles too: (angle ctr pt1)(angle ctr pt2)
  ;;; returns nil on a straight segment!
  ;;; (bugfixed version. Thanks to Sergei Komarov)
  (defun SEG2CIR (seg / bulge p1 p2 cot x y rad dummy)
    (if (zerop (car seg))  ;straight line => invalid circle
      nil
      (setq bulge (car seg) p1 (cadr seg) p2 (caddr seg)
        cot (* 0.5 (- (/ 1.0 bulge) bulge))
        x (/ (- (+ (car  p1) (car  p2))
                (* (- (cadr p2) (cadr p1)) cot)) 2.0)
        y (/ (+ (+ (cadr p1) (cadr p2))
                (* (- (car  p2) (car  p1)) cot)) 2.0)
        rad (distance (list (car p1) (cadr p1)) (list x y))
        dummy (list (list x y) rad))))   ; return this, I hate progn's