convert ellipse to polyline
You can try the following routine.
It defines 2 commands:
EL2PL to convert the selected ellipses and elliptcal arcs into polylines
PELL to draw on the fly a polyline which is an approximation of ellipse or elliptical arc
The generated polylines are similar to the ones generated by AutoCAD when PELLIPSE system variable is equal to 1.
;; EllipseToPolyline
;; Returns a polyline (vla-object) which is an approximation of the ellipse (or elliptical arc)
;;
;; Argument : an ellipse (vla-object)
(defun EllipseToPolyline (el / cl norm cen elv pt0 pt1 pt2 pt3 pt4 ac0
ac4 a04 a02 a24 bsc0 bsc2 bsc3 bsc4 plst blst spt spa
fspa srat ept epa fepa erat n
)
(vl-load-com)
(setq cl (= (ang<2pi (vla-get-StartAngle el))
(ang<2pi (vla-get-EndAngle el)))
norm (vlax-get el 'Normal)
cen (trans (vlax-get el 'Center) 0 norm)
elv (caddr cen)
cen (3dTo2dPt cen)
pt0 (mapcar '+ (trans (vlax-get el 'MajorAxis) 0 norm) cen)
ac0 (angle cen pt0)
pt4 (mapcar '+ cen (trans (vlax-get el 'MinorAxis) 0 norm))
pt2 (3dTo2dPt (trans (vlax-curve-getPointAtparam el (/ pi 4.)) 0 norm))
ac4 (angle cen pt4)
a04 (angle pt0 pt4)
a02 (angle pt0 pt2)
a24 (angle pt2 pt4)
bsc0 (/ (ang<2pi (- a02 ac4)) 2.)
bsc2 (/ (ang<2pi (- a04 a02)) 2.)
bsc3 (/ (ang<2pi (- a24 a04)) 2.)
bsc4 (/ (ang<2pi (- (+ ac0 pi) a24)) 2.)
pt1 (inters pt0
(polar pt0 (+ ac0 (/ pi 2.) bsc0) 1.)
pt2
(polar pt2 (+ a02 bsc2) 1.)
nil
)
pt3 (inters pt2
(polar pt2 (+ a04 bsc3) 1.)
pt4
(polar pt4 (+ a24 bsc4) 1.)
nil
)
plst (list pt4 pt3 pt2 pt1 pt0)
blst (mapcar '(lambda (b) (tan (/ b 2.)))
(list bsc4 bsc3 bsc2 bsc0)
)
)
(foreach b blst
(setq blst (cons b blst))
)
(foreach b blst
(setq blst (cons b blst))
)
(foreach p (cdr plst)
(setq ang (angle cen p)
plst (cons
(polar cen (+ ang (* 2 (- ac4 ang))) (distance cen p))
plst
)
)
)
(foreach p (cdr plst)
(setq ang (angle cen p)
plst (cons
(polar cen (+ ang (* 2 (- ac0 ang))) (distance cen p))
plst
)
)
)
(setq pl
(vlax-invoke
(vla-get-ModelSpace (vla-get-ActiveDocument (vlax-get-acad-object)))
'AddLightWeightPolyline
(apply 'append
(setq plst
(reverse (if cl
(cdr plst)
plst
)
)
)
)
)
)
(vlax-put pl 'Normal norm)
(vla-put-Elevation pl elv)
(mapcar '(lambda (i v) (vla-SetBulge pl i v))
'(0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16)
blst
)
(if cl
(vla-put-Closed pl :vlax-true)
(progn
(setq spt (vlax-curve-getClosestPointTo pl (vlax-get el 'Startpoint))
spa (vlax-curve-getParamAtPoint pl spt)
fspa (fix spa)
ept (vlax-curve-getClosestPointTo pl (vlax-get el 'Endpoint))
epa (vlax-curve-getParamAtPoint pl ept)
fepa (fix epa)
n 0
)
(cond
((equal spt (trans pt0 norm 0) 1e-9)
(if (= epa fepa)
(setq plst (sublist plst 0 (1+ fepa))
blst (sublist blst 0 (1+ fepa))
)
(setq erat (/ (- (vlax-curve-getDistAtParam pl epa)
(vlax-curve-getDistAtParam pl fepa)
)
(- (vlax-curve-getDistAtParam pl (rem (1+ fepa) 17))
(vlax-curve-getDistAtParam pl fepa)
)
)
plst (append (sublist plst 0 (1+ fepa))
(list (3dTo2dPt (trans ept 0 norm)))
)
blst (append (sublist blst 0 (1+ fepa))
(list (k*bulge (nth fepa blst) erat))
)
)
)
)
((equal ept (trans pt0 norm 0) 1e-9)
(if (= spa fspa)
(setq plst (sublist plst fspa nil)
blst (sublist blst fspa nil)
)
(setq srat (/ (- (vlax-curve-getDistAtParam pl (rem (1+ fspa) 17))
(vlax-curve-getDistAtParam pl spa)
)
(- (vlax-curve-getDistAtParam pl (rem (1+ fspa) 17))
(vlax-curve-getDistAtParam pl fspa)
)
)
plst (cons (3dTo2dPt (trans spt 0 norm))
(sublist plst (1+ fspa) nil)
)
blst (cons (k*bulge (nth fspa blst) srat)
(sublist blst (1+ fspa) nil)
)
)
)
)
(T
(setq srat (/ (- (vlax-curve-getDistAtParam pl (rem (1+ fspa) 17))
(vlax-curve-getDistAtParam pl spa)
)
(- (vlax-curve-getDistAtParam pl (rem (1+ fspa) 17))
(vlax-curve-getDistAtParam pl fspa)
)
)
erat (/ (- (vlax-curve-getDistAtParam pl epa)
(vlax-curve-getDistAtParam pl fepa)
)
(- (vlax-curve-getDistAtParam pl (rem (1+ fepa) 17))
(vlax-curve-getDistAtParam pl fepa)
)
)
)
(if (< epa spa)
(setq plst (append
(if (= spa fspa)
(sublist plst fspa nil)
(cons (3dTo2dPt (trans spt 0 norm))
(sublist plst (1+ fspa) nil)
)
)
(cdr (sublist plst 0 (1+ fepa)))
(if (/= epa fepa)
(list (3dTo2dPt (trans ept 0 norm)))
)
)
blst (append
(if (= spa fspa)
(sublist blst fspa nil)
(cons
(k*bulge (nth fspa blst) srat)
(sublist blst (1+ fspa) nil)
)
)
(sublist blst 0 fepa)
(if (= epa fepa)
(list (nth fepa blst))
(list (k*bulge (nth fepa blst) erat))
)
)
)
(setq plst (append
(if (= spa fspa)
(sublist plst fspa (1+ (- fepa fspa)))
(cons (3dTo2dPt (trans spt 0 norm))
(sublist plst (1+ fspa) (- fepa fspa))
)
)
(list (3dTo2dPt (trans ept 0 norm)))
)
blst (append
(if (= spa fspa)
(sublist blst fspa (- fepa fspa))
(cons
(k*bulge (nth fspa blst) srat)
(sublist blst (1+ fspa) (- fepa fspa))
)
)
(if (= epa fepa)
(list (nth fepa blst))
(list (k*bulge (nth fepa blst) erat))
)
)
)
)
)
)
(vlax-put pl 'Coordinates (apply 'append plst))
(foreach b blst
(vla-SetBulge pl n b)
(setq n (1+ n))
)
)
)
pl
)
;; Ang<2pi
;; Returns the angle expression betweem 0 and 2*pi
(defun ang<2pi (ang)
(if (and (<= 0 ang) (< ang (* 2 pi)))
ang
(ang<2pi (rem (+ ang (* 2 pi)) (* 2 pi)))
)
)
;; 3dTo2dPt
;; Returns the 2d point (x y) of a 3d point (x y z)
(defun 3dTo2dPt (pt) (list (car pt) (cadr pt)))
;; Tan
;; Returns the angle tangent
(defun tan (a) (/ (sin a) (cos a)))
;; SUBLIST
;; Returns a sub list
;;
;; Arguments
;; lst : a list
;; start : start index (first item = 0)
;; leng : the sub list length (number of items) or nil
(defun sublist (lst start leng / n r)
(if (or (not leng) (< (- (length lst) start) leng))
(setq leng (- (length lst) start))
)
(setq n (+ start leng))
(while (< start n)
(setq r (cons (nth (setq n (1- n)) lst) r))
)
)
;; K*BULGE
;; Returns the proportinal bulge to the référence bulge
;; Arguments :
;; b : the bulge
;; k : the proportion ratio (between angles or arcs length)
(defun k*bulge (b k / a)
(setq a (atan b))
(/ (sin (* k a)) (cos (* k a)))
)
;; EL2PL
;; Converts ellipses and elliptcal arcs into polylines
(defun c:el2pl (/ *error* fra acdoc ss)
(vl-load-com)
(defun *error* (msg)
(if (and (/= msg "Fonction annulée")
(/= msg "Function cancelled")
)
(princ (strcat (if (= "FRA" (getvar 'locale))
"\nErreur: "
"\Error: "
)
msg
)
)
)
(vla-endUndoMark acdoc)
(princ)
)
(setq acdoc (vla-get-ActiveDocument (vlax-get-acad-object)))
(if (ssget '((0 . "ELLIPSE")))
(progn
(vla-StartUndoMark acdoc)
(vlax-for e (setq ss (vla-get-ActiveSelectionSet acdoc))
(EllipseToPolyline e)
(vla-delete e)
)
(vla-delete ss)
(vla-EndUndoMark acdoc)
)
)
(princ)
)
;; PELL
;; Draws an ellipse or an elliptical arc approximation (polyline) on the fly
(defun c:pell (/ *error* ec pe old ent)
(vl-load-com)
(defun *error* (msg)
(if (and msg
(/= msg "Fonction annulée")
(/= msg "Function cancelled")
)
(princ (strcat (if (= "FRA" (getvar 'locale))
"\nErreur: "
"\Error: "
)
msg
)
)
)
(setvar 'cmdecho ec)
(setvar 'pellipse pe)
(princ)
)
(setq ec (getvar 'cmdecho)
pe (getvar 'pellipse)
old (entlast)
)
(setvar 'cmdecho 1)
(setvar 'pellipse 0)
(command "_.ellipse")
(while (/= 0 (getvar 'cmdactive))
(command pause)
)
(if (not (eq old (setq ent (entlast))))
(progn
(EllipseToPolyline (vlax-ename->vla-object ent))
(entdel ent)
)
)
(*error* nil)
)
Be aware that an Ellipse made with PELLIPSE = 1 has only 16 vertices, and is an approximation of a true elliptical shape. It may be plenty precise for your purposes, but if you need greater accuracy, you can do this:
Use ReverseDirection.lsp and its RD command, available >here<. It can reverse the direction of various things that AutoCAD's REVERSE command cannot, and in the case of an Ellipse, it does it by making a Spline running the other way [if you agree to that -- you will be asked whether to convert it]. It asks for a precision, and you can ask for any number of defining points you want. It offers 24 as the initial default, which is already of higher precision than AutoCAD's ellipse-approximating Polyline, but you can ask for thousands if you like. Then you can use SPLINEDIT to convert the resulting Spline to a Polyline if that's what you need, in which command you will also be asked for a precision.
@_gile wrote:
One advantage of the polyline approximation is that it only contains circular arcs.
Some CNC machines do not like ellipses, and generally hate splines.
That's why I suggested SPLINEDIT at the end, to convert it. That also results in an all-arc-segment Polyline, which can be to any desired higher degree of accuracy in tracing a true elliptical shape [again -- if needed, which it may not be for most people's purposes].
@MikeKovacik4928 wrote:
.... wipeouts work only with straight line segments....
If you're still interested [maybe not, in light of the latest Messages], there is a way to convert an Ellipse directly into a straight-line-segments-only Polyline, using a no-wobble application of the WPL command in WobblyPline.lsp -- check >this< out [it's even about that specific task, though applicable much more widely].
