Polyline

How to know if the polyline is a circle or other figure.

I would like to detect polylines in a circle.

Thank you.

Removed ...

Do you mean that you wish to detect whether a polyline has the visual appearance of a circle?

yes Lee

Thank you

Not sure if you are looking for polylines with only the vertex on a circle, or polylines exactly like a circle (with bulges).

For the last hypothesis:

(defun is_circle (e / i o c1 c2 p1 p2)
 (setq i (vlax-curve-getendparam e)
       o T)
 (while (and (> i 0) o)
   (setq p1 (vlax-curve-getpointatparam e i)
         p2 (vlax-curve-getpointatparam e (setq i (1- i)))
         c1 (mapcar
              (if (minusp (vla-getbulge (vlax-ename->vla-object e) i)) '- '+)
              p2 (vlax-curve-getsecondderiv e i)
            )
         )
   (or
     (equal p1 p2 1e-
     (if (not c2) (setq c2 c1))
     (setq o (equal c1 c2 1e-)
     )
   )
 o
 )

(defun c:test ( / e)
 (if
   (setq e (ssget ":E:S" '((0 . "LWPOLYLINE"))))
   (if
     (is_circle (ssname e 0))
     (alert "Selected object lies on a CIRCLE")
     (alert "Not a circle")
     )
   )
 (princ)
 )

Very good Stefan

Here is a crude & unimaginative method:

(defun polycircle-p ( ent / _circle-p _vertexdata )

   (defun _vertexdata ( enx )
       (if (setq enx (member (assoc 10 enx) enx))
           (cons
               (list
                   (cdr (assoc 10 enx))
                   (cdr (assoc 42 enx))
               )
               (_vertexdata (cdr enx))
           )
       )
   )
   (defun _circle-p ( lst cn1 rd1 / ang cn2 rd2 )
       (or (not (cdr lst))
           (and
               (or (equal (caar lst) (caadr lst) 1e-
                   (and
                       (not (equal 0.0 (cadar lst) 1e-)
                       (setq ang (* 2 (atan (cadar lst)))
                             rd2 (/ (distance (caar lst) (caadr lst)) 2 (sin ang))
                             cn2 (polar (caar lst) (+ (- (/ pi 2) ang) (angle (caar lst) (caadr lst))) rd2)
                       )
                       (or (null cn1)
                           (and (equal cn1 cn2 1e- (equal rd1 rd2 1e-)
                       )
                       (_circle-p (cdr lst) cn2 rd2)
                   )
               )
           )
       )
   )
   (and
       (setq enx (entget ent))
       (= "LWPOLYLINE" (cdr (assoc 0 enx)))
       (= 1 (logand 1 (cdr (assoc 70 enx))))
       (cdr (setq lst (_vertexdata enx)))
       (_circle-p (cons (last lst) lst) nil nil)
   )
)

http://forums.autodesk.com/t5/visual-lisp-autolisp-and-general/circle-to-polyline-circular-polyline-to-circle/m-p/5520233#M330236

CirclePolylineSwap.lsp [command names: C2P & P2C] by Kent Cooper, last edited 25 February 2015

Updated one is post #27

Guessing when you find them you may want to change them to circles.

Thank you very much to all