[求助]如何画出圆弧的两个切线

linshiyin2 · 发表于 2010-5-29 18:26:00

已知一个多段线的圆弧，如何画出切线部分？（蓝色的两条直线），请高人给出lisp，多谢

技术工作室 · 发表于 2023-10-3 19:33:29

正是我想要的，赞一个

linshiyin2 · 发表于 2010-5-29 18:46:00

给点帮助

;;;
;;;选择并计算曲线参数函数DimSelqx
;;;返回值:曲线参数(alfa[弧度] R[mm])
;;;
(defun DimSelqx( / wh ss ssLen i alfa R Ename vdata N p1 p2 bulge alfai XL Ri)

(setq wh 1 ss nil)
(while (and (= wh 1) (setq ss (ssget '((0 . "LWPOLYLINE")))) )
     (setq ssLen (sslength ss))
     (setq i 0 wh 0 R 0 alfa 0)
     (while (and (= wh 0) (< i ssLen))
        (setq Ename (ssname ss i))
        (setq vdata (entget Ename))
        (setq N (length vdata))
        (setq p1 (cdr (nth (- N 9) vdata))       ;第一个顶点
              p2 (cdr (nth (- N 5) vdata)))      ;第二个顶点
        (setq bulge (cdr (nth (- N 6) vdata)))   ;第一个顶点凸度
        (if (/= bulge 0)
           (progn (setq alfai (* 4 (atan (abs bulge)))
                        XL (distance p1 p2)
                        Ri (ccfix (/ (/ XL 2) (sin (/ alfai 2))) 0))
                   (if (and (/= R Ri) (/= i 0))
                      (progn (redraw Ename 3)
                             (alert "曲线半径不同，请重新选择!")
                             (redraw Ename 4)
                             (setq wh 1)
                      )
                      (setq alfa (+ alfai alfa)   R Ri)
                   )
           )
           (progn (redraw Ename 3)
                  (alert "虚显的巷道是直线，请重新选择!")
                  (redraw Ename 4)
                  (setq wh 1)
           )
        )
        (setq i (1+ i))
     )
)
(if (not ss) (exit) )
(setq ss nil)

(list alfa R)

);End DimSelqx

linshiyin2 · 发表于 2010-5-31 08:47:00

沉的好快，自己顶顶，有哪位大侠给指点一下啊

sailorcwx · 发表于 2010-5-31 15:48:00

求出圆心，然后求出圆心和切点的角度，然后。。。。。出来了吧

linshiyin2 · 发表于 2010-5-31 16:31:00

楼上的，我不会做啊，能给个lisp吗

xianaihua · 发表于 2010-5-31 18:02:00

我这有一个程序，你可试试

;虚拟交点的绘制
(defun C:XNJD (/ p1 p2 p3 p4 p5)
(setvar "cmdecho" 0)
(setq p1 (entsel "\n选取一段圆弧: "))
(if p1
(progn (setq p0 (entget (car p1)))
(setq p1 (cdr (assoc 0 p0)))
)
)
(if (/= p1 "ARC")
(prompt "\n选择的不是圆弧,请再试...")
)
(setq p1 (polar (cdr (assoc 10 p0))
(cdr (assoc 50 p0))
(cdr (assoc 40 p0))
)
p2 (polar (cdr (assoc 10 p0))
(cdr (assoc 51 p0))
(cdr (assoc 40 p0))
)
p3 (polar p1
(+ (/ pi 2) (cdr (assoc 50 p0)))
(cdr (assoc 40 p0))
)
p4 (polar p2
(+ (/ pi 2) (cdr (assoc 51 p0)))
(cdr (assoc 40 p0))
)
p5 (inters p1 p3 p2 p4 nil)
)
(if (not p5)
(prompt "\n没有交点...")
(progn
(if (> (distance p1 p5)
(* 2 (getvar "dimscale") (getvar "dimexo"))
)
(command
"_.line"
(polar p1
(angle p1 p5)
(* (getvar "dimexo") (getvar "dimscale"))
)
(polar p5
(angle p1 p5)
(* (getvar "dimexe") (getvar "dimscale"))
)
""
"_.line"
(polar p2
(angle p2 p5)
(* (getvar "dimexo") (getvar "dimscale"))
)
(polar p5
(angle p2 p5)
(* (getvar "dimexe") (getvar "dimscale"))
)
""
)
(command
"_.line"
(polar p1 (angle p1 p5) (* 0.5 (distance p1 p5)))
(polar p5
(angle p1 p5)
(* (getvar "dimexe") (getvar "dimscale"))
)
""
"_.line"
(polar p2 (angle p2 p5) (* 0.5 (distance p2 p5)))
(polar p5
(angle p2 p5)
(* (getvar "dimexe") (getvar "dimscale"))
)
""
)
)
)
)
(princ)
)

;虚拟交点的绘制
(defun C:XNJD (/ p1 p2 p3 p4 p5)
  (setvar "cmdecho" 0)
  (setq p1 (entsel "\n选取一段圆弧: "))
  (if p1
    (progn (setq p0 (entget (car p1)))
    (setq p1 (cdr (assoc 0 p0)))
    )
  )
  (if (/= p1 "ARC")
    (prompt "\n选择的不是圆弧,请再试...")
  )
  (setq p1 (polar (cdr (assoc 10 p0))
    (cdr (assoc 50 p0))
    (cdr (assoc 40 p0))
    )
 p2 (polar (cdr (assoc 10 p0))
    (cdr (assoc 51 p0))
    (cdr (assoc 40 p0))
    )
 p3 (polar p1
    (+ (/ pi 2) (cdr (assoc 50 p0)))
    (cdr (assoc 40 p0))
    )
 p4 (polar p2
    (+ (/ pi 2) (cdr (assoc 51 p0)))
    (cdr (assoc 40 p0))
    )
 p5 (inters p1 p3 p2 p4 nil)
  )
  (if (not p5)
    (prompt "\n没有交点...")
    (progn
      (if (> (distance p1 p5)
      (* 2 (getvar "dimscale") (getvar "dimexo"))
   )
 (command
   "_.line"
   (polar p1
   (angle p1 p5)
   (* (getvar "dimexo") (getvar "dimscale"))
   )
   (polar p5
   (angle p1 p5)
   (* (getvar "dimexe") (getvar "dimscale"))
   )
   ""
   "_.line"
   (polar p2
   (angle p2 p5)
   (* (getvar "dimexo") (getvar "dimscale"))
   )
   (polar p5
   (angle p2 p5)
   (* (getvar "dimexe") (getvar "dimscale"))
   )
   ""
 )
 (command
   "_.line"
   (polar p1 (angle p1 p5) (* 0.5 (distance p1 p5)))
   (polar p5
   (angle p1 p5)
   (* (getvar "dimexe") (getvar "dimscale"))
   )
   ""
   "_.line"
   (polar p2 (angle p2 p5) (* 0.5 (distance p2 p5)))
   (polar p5
   (angle p2 p5)
   (* (getvar "dimexe") (getvar "dimscale"))
   )
   ""
 )
      )
    )
  )
  (princ)
)

狂刀无痕 · 发表于 2010-6-1 00:23:00

一个偏门的方法：

(command "fillet" "r" 0. "p" 选pl线)

linshiyin2 · 发表于 2010-6-1 08:27:00

楼上的偏方倒是可以，但是，我要的是另外两条切线，用倒角的话会延长这两条线，而不是画两条新的切线，不过还是非常感谢你哦，这个思路也行，就是通过两条边画这个焦点切线

linshiyin2 · 发表于 2010-6-1 08:30:00

感谢xianaihua问题是你的针对是圆弧，我这个是多段线构成的圆弧，怎么样修改一下你的程序呢，还有你的程序实际使用时，圆弧下凸就会有多余的部分，p3点计算出错

wzs07 · 发表于 2010-6-1 08:52:00

以上的代码不错啊

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[基础] [求助]如何画出圆弧的两个切线

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