Topic: weed pline by angle

[mohobrien]

I have a pline that defines the boundary of a parcel. The pline is zero width and no special properties. I want to simplify the pline so that only major changes of direction, say more than 45° will be shown. All bends in the line are close to 90° so if I use 45 I should get what I want. I'm not interested in how far apart the vertices are. This little snippet is what I am using to weed the extra vertices. Most of the time it works, but sometimes it misses vetices to remove and sometimes removes what it shouldn't. I think it is a problem with my angle test. Any ideas? finalcoordlist is just that and newcoordlist is the unweeded list.

Code: [Select]

;;;            remove vertices if major change in direction
(setq finalcoordlist
       newcoordlist
      counter 0
)
(repeat (- (length newcoordlist) 2)
  (setq pt1 (nth counter newcoordlist))
  (setq pt2 (nth (+ counter 1) newcoordlist))
  (setq pt3 (nth (+ counter 2) newcoordlist))
  (if
    (< (abs (- (angle pt1 pt2) (angle pt2 pt3)))
       (* (/ 45.0 180.0) pi)
    )
     (setq finalcoordlist
    (vl-remove (nth (+ counter 1) newcoordlist)
       finalcoordlist
    )
   counter (1+ counter)
     )
     (setq counter (1+ counter))
  )
)


[DEVITG]

Hi , can you upload some dwg sample .?

[CAB]

Make use of the function vlax-curve-getFirstDeriv like this

Code: [Select]

(defun C:TEST ()
  (vl-load-com)
  (setq curve (car (entsel "\nSelect polyline: ")))
  (setq end_param (vlax-curve-getendparam curve))

  (setq par 0)
  (repeat (fix end_param)
    (print (angle '(0 0) (vlax-curve-getFirstDeriv curve par)))
    (setq par (1+ par))
  )

  (princ)
)

[DEVITG]

;;;Hi Cab I did a test with your lisp , an it give not the , say, included angle among two consecutive lines .
;;;This is so, because  the first derivative [ FD ] give the  tangent of a curve at that point,
;;or also it give the idea how the curve is growing or decaying at that point.
;;;When curve is a line ,  it give the  tangent at that point that in this case is the same as the line angle.
;;;Also in this case , I do not know if ACAD take the value for the ending line or starting line at a given parameter.
;;;I think that if we take  the  the FD at ( - param 0.1)  , and at (+  param 0.1) , it will give 2 angles , and from it,
;; we can get angle between the lines.Not so sure.
;;;I'm doing now some test .
;;;From it I knew that the FD at Param give the angle for the after the param 
 

[CAB]

DEVITG,
Try this code:

Code: [Select]

(defun C:TEST (/ curve end_param par MinAng LastAng RemoveLst)
  (vl-load-com)
  (setq curve (car (entsel "\nSelect polyline: ")))
  (setq end_param (vlax-curve-getendparam curve))

  (setq par 0
        MinAng (/ pi 4) ; 45 deg
        )
  (repeat (fix end_param)
    (cond
      ((null LastAng) ; get the ang of the first segment
       (setq LastAng (angle '(0 0) (vlax-curve-getFirstDeriv curve par))))
      ((< (abs (- LastAng
               (setq LastAng (angle '(0 0) (vlax-curve-getFirstDeriv curve par)))))
          MinAng)
       (setq RemoveLst (cons par RemoveLst))
               
       )
      )
    (setq par (1+ par))
  )
  (if RemoveLst ; need to remove these vertex
    (princ RempveLst)
  )

  (princ)
)

[DEVITG]

Hi Cab, please can you check it on this dwg .
I did it , and I got NIL

maybe I´m doing something wrong.

[CAB]

Yes, all those angles are greater than 45 degrees.

See attached drawing.

[DEVITG]

Hi Cab ,  I toke a bad concept ,
I thought it was internal angles  at  the polyline .
Now I got it, it  was deviation angle from the prior segment .
cause my poor English.
 


 

[CAB]

OK

[DEVITG]

Hi Cad , and how it can be get the "internal"  angle of a poly ?

[fixo]

Hi Cad , and how it can be get the "internal"  angle of a poly ?

Cad? Who is it?

[DEVITG]

Hi Cad , and how it can be get the "internal"  angle of a poly ?

Cad? Who is it?

 Sorry  , a typo error , because CAB know a lot of CAD , I had miss spelling or lapsus, or   Fehlleistung in german .