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")
(setq
disttemp
(getdist
(strcat
"\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
*distmax*
(cond
(disttemp); user entered number or picked distance
(T *distmax*); otherwise, user hit Enter - keep value
); end cond & *distmax*
cidtemp
(getangle
(strcat
"\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
*cidmax*
(cond
(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")
(setq
arctemp
(getkword
(strcat
"\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
*arcstr*
(cond
(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: ")
(cond
((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:
(progn
(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
(setq
front ; list of "front end" [pre-vertices] entries, minus entity names & handle
(vl-remove-if
'(lambda (x)
(member (car x) '(-1 330 5 10 40 41 42 210))
); end lambda
pldata
); end removal & front
10to42 ; list of all code 10, 40, 41, 42 entries only
(vl-remove-if-not
'(lambda (x)
(member (car x) '(10 40 41 42))
); end lambda
pldata
); 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")
(progn
(setq bulges ; find any bulge factors
(vl-remove-if-not
'(lambda (x)
(and
(= (car x) 42)
(/= (cdr x) 0.0)
); end and
); end lambda
10to42
); 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
(setq
verts ; sub-group list: separate list of four entries for each vertex
(cons
(list
(nth (- (* vinc 4) 4) 10to42)
(nth (- (* vinc 4) 3) 10to42)
(nth (- (* vinc 4) 2) 10to42)
(nth (1- (* vinc 4)) 10to42)
); end list
verts
); 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
(if
(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
(setq
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
(if
(or
(equal ang1 ang2 0.0001); collinear, ignoring distance
(and
(<= (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
*cidmax*
); 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
(setq
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
(progn
(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)
(princ)
); end defun - PLD
(prompt "\nType PLD to put PolyLines on a Diet.")
```