I have a polyline (lines only) which has about 500 points in it. I would like to reduce the number of points in it. How can I do it in AutoCAD? (or may be some other application)?

P.S. Polylines were made of splines converted into set of lines. But the level of detail is too high I want to decrease it.

6 Answers 6


This LISP script does the job. Create an LSP file and add it to AutoCAD, then use PLD command to run it.

;;;  PLDIET.lsp [command name: PLD]
;;;  To put lightweight PolyLines on a DIET (remove excess vertices); usually
;;;    used for contours with too many too-closely-spaced vertices.
;;;  Concept from PVD routine [posted on AutoCAD Customization Discussion
;;;    Group by oompa_l, July 2009] by Brian Hailey, added to by CAB, and
;;;    WEED and WEED2 routines by Skyler Mills at Cadalyst CAD Tips [older
;;;    routines for "heavy" Polylines that won't work on newer lightweight ones];
;;;    simplified in entity data list processing, and enhanced in other ways [error
;;;    handling, default values, join collinear segments beyond max. distance,
;;;    limit to current space/tab, account for change in direction across 0 degrees,
;;;    option to keep or eliminate arc segments] by Kent Cooper, August 2009.
(defun C:PLD
  (/ *error* cmde disttemp cidtemp arctemp plinc plsel pldata
  ucschanged front 10to42 vinc verts vert1 vert2 vert3)
  (defun *error* (errmsg)
    (if (not (wcmatch errmsg "Function cancelled,quit / exit abort"))
      (princ (strcat "\nError: " errmsg))
    ); end if
    (if ucschanged (command "_.ucs" "_prev"))
      ; ^ i.e. don't go back unless routine reached UCS change but didn't change back
    (command "_.undo" "_end")
    (setvar 'cmdecho cmde)
  ); end defun - *error*
  (setq cmde (getvar 'cmdecho))
  (setvar 'cmdecho 0)
  (command "_.undo" "_begin")
          "\nMaximum distance between non-collinear vertices to straighten"
          (if *distmax* (strcat " <" (rtos *distmax* 2 2) ">") ""); default only if not first use
          ": "
        ); end strcat
      ); end getdist & disttemp
        (disttemp); user entered number or picked distance
        (T *distmax*); otherwise, user hit Enter - keep value
      ); end cond & *distmax*
          "\nMaximum change in direction to straighten"
          (strcat ; offer prior choice if not first use; otherwise 15 degrees
            " <"
            (if *cidmax* (angtos *cidmax*) (angtos (/ pi 12)))
          ); end strcat
          ": "
        ); end strcat
      ); end getdist & cidtemp
        (cidtemp); user entered number or picked angle
        (*cidmax*); Enter with prior value set - use that
        (T (/ pi 12)); otherwise [Enter on first use] - 15 degrees
      ); end cond & *cidmax*
    plinc 0 ; incrementer through selection set of Polylines
  ); end setq
  (initget "Retain Straighten")
          "\nRetain or Straighten arc segments [R/S] <"
          (if *arcstr* (substr *arcstr* 1 1) "S"); at first use, S default; otherwise, prior choice
          ">: "
        ); end strcat
      ); end getkword
        (arctemp); if User typed something, use it
        (*arcstr*); if Enter and there's a prior choice, keep that
        (T "Straighten"); otherwise [Enter on first use], Straighten
      ); end cond & *arcstr*
  ); end setq
  (prompt "\nSelect LWPolylines to put on a diet, or press Enter to select all: ")
    ((setq plsel (ssget '((0 . "LWPOLYLINE"))))); user-selected Polylines
    ((setq plsel (ssget "X" (list '(0 . "LWPOLYLINE") (cons 410 (getvar 'ctab))))))
      ; all Polylines [in current space/tab only]
  ); end cond
  (repeat (sslength plsel)
    (setq pldata (entget (ssname plsel plinc)))
    (if (/= (cdr (last pldata)) (trans '(0 0 1) 1 0)); extr. direction not parallel current CS
        ; for correct angle & distance calculations [projected onto current construction
        ; plane], since 10-code entries for LWPolylines are only 2D points:
        (command "_.ucs" "_new" "_object" (ssname plsel plinc)) ; set UCS to match object
        (setq ucschanged T) ; marker for *error* to reset UCS if routine doesn't
      ); end progn
    ); end if
      front ; list of "front end" [pre-vertices] entries, minus entity names & handle
          '(lambda (x)
            (member (car x) '(-1 330 5 10 40 41 42 210))
          ); end lambda
        ); end removal & front
      10to42 ; list of all code 10, 40, 41, 42 entries only
          '(lambda (x)
            (member (car x) '(10 40 41 42))
          ); end lambda
        ); end removal & 10to42
      vinc (/ (length 10to42) 4); incrementer for vertices within each Polyline
      verts nil ; eliminate from previous Polyline [if any]
    ); end setq
    (if (= *arcstr* "Straighten")
        (setq bulges ; find any bulge factors
            '(lambda (x)
                (= (car x) 42)
                (/= (cdr x) 0.0)
              ); end and
            ); end lambda
          ); end removal & bulges
        ); end setq
        (foreach x bulges (setq 10to42 (subst '(42 . 0.0) x 10to42)))
          ; straighten all arc segments to line segments
      ); end progn
    ); end if
    (repeat vinc
        verts ; sub-group list: separate list of four entries for each vertex
              (nth (- (* vinc 4) 4) 10to42)
              (nth (- (* vinc 4) 3) 10to42)
              (nth (- (* vinc 4) 2) 10to42)
              (nth (1- (* vinc 4)) 10to42)
            ); end list
          ); end cons & verts
        vinc (1- vinc) ; will be 0 at end
      ); end setq
    ); end repeat
    (while (nth (+ vinc 2) verts); still at least 2 more vertices
        (or ; only possible if chose to Retain arc segments
          (/= (cdr (assoc 42 (nth vinc verts))) 0.0); next segment is arc
          (/= (cdr (assoc 42 (nth (1+ vinc) verts))) 0.0); following segment is arc
        ); end or
        (setq vinc (1+ vinc)); then - don't straighten from here; move to next
        (progn ; else - analyze from current vertex
            vert1 (cdar (nth vinc verts)) ; point-list location of current vertex
            vert2 (cdar (nth (1+ vinc) verts)); of next one
            vert3 (cdar (nth (+ vinc 2) verts)); of one after that
            ang1 (angle vert1 vert2)
            ang2 (angle vert2 vert3)
          ); end setq
              (equal ang1 ang2 0.0001); collinear, ignoring distance
                (<= (distance vert1 vert3) *distmax*)
                  ; straightens if direct distance from current vertex to two vertices later is
                  ; less than or equal to maximum; if preferred to compare distance along
                  ; Polyline through intermediate vertex, replace above line with this:
                  ; (<= (+ (distance vert1 vert2) (distance vert2 vert3)) *distmax*)
                  (if (> (abs (- ang1 ang2)) pi); if difference > 180 degrees
                    (+ (min ang1 ang2) (- (* pi 2) (max ang1 ang2)))
                      ; then - compensate for change in direction crossing 0 degrees
                    (abs (- ang1 ang2)); else - size of difference
                  ); end if
                ); end <=
              ); end and
            ); end or
            (setq verts (vl-remove (nth (1+ vinc) verts) verts))
              ; then - remove next vertext, stay at current vertex for next comparison
            (setq vinc (1+ vinc)); else - leave next vertex, move to it as new base
          ); end if - distance & change in direction analysis
        ); end progn - line segments
      ); end if - arc segment check
    ); end while - working through vertices
      front (subst (cons 90 (length verts)) (assoc 90 front) front)
        ; update quantity of vertices for front end
      10to42 nil ; clear original set
    ); end setq
    (foreach x verts (setq 10to42 (append 10to42 x)))
      ; un-group four-list vertex sub-lists back to one list of all 10, 40, 41, 42 entries
    (setq pldata (append front 10to42 (list (last pldata))))
      ; put front end, vertex entries and extrusion direction back together
    (entmake pldata)
    (entdel (ssname plsel plinc)); remove original
    (setq plinc (1+ plinc)); go on to next Polyline
    (if ucschanged
        (command "_.ucs" "_prev")
        (setq ucschanged nil) ; eliminate UCS reset in *error* since routine did it already
      ); end progn
    ); end if - UCS reset
  ); end repeat - stepping through set of Polylines
  (command "_.undo" "_end")
  (setvar 'cmdecho cmde)
); end defun - PLD
(prompt "\nType PLD to put PolyLines on a Diet.")
  • Works on the Mac version too. Thanks
    – hmedia1
    Aug 18, 2020 at 2:07

I wrote a utility call Reduce that does this. It is a compiled Autolisp fas file, which is run like a normal lsp file. You can download it here https://www.theswamp.org/index.php?topic=27724.0.

  • 1
    That link requires registration.
    – DavidPostill
    Apr 19, 2016 at 22:57
  • That link is worth the registration, it works brilliantly.
    – CAD bloke
    Sep 20, 2017 at 23:35

The lisp routine may be the best deal for you, but I use the overkill command to remove points from polylines (when the command is active, go to settings). It is an express tool that is usually used to remove duplicate lines but it works to optimize polylines. The one thing you need to be careful of is when your polyline has a width. Overkill will usually kill widths.



  • 1
    OVERKILL remove only overlapped segments on polylines. It reduces the number of points only in this case.
    – Maxence
    May 11, 2011 at 10:17

I have had this problem to and I usually just explode the polyline, then do an overkill and then join the remaining lines. I have 2014 LT so lisp routines wouldn't work for me. It was the only way that I could do it.


If you have rhino, "SimplifyCrv" works pretty well. Not sure how it functions, but I had a similar problem, and this command was able to lower the number of control points in a polyline beyond commands that come loaded with autoCAD.


Please see image here:

enter image description here

This is a very good utility for PLine to reduce file size. But in above case, if 2 green points was deleted, the PLine become sharp (not tangent). Please consider about it.


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