Unable to get Intersection point between two 3d polyline in Autocad visual lisp

[nagamalliv]

Hi,

Unable to get intersection point of 3dpolylines in Autocad visual lisp/ .NET.

[Alexander.Rivilis]

Maybe you show your code?

[nagamalliv]

(defun GetIntersectPoints
(sourName destName
/ sourObj destObj intPnts)
(setq sourObj (vlax-ename->vla-object sourName)
destObj (vlax-ename->vla-object destName)
intPnts (vlax-invoke-method sourObj 'intersectwith destObj acExtendThisentity)
);setq

(mapcar 'vlax-release-object (list sourObj destObj))
(setq intPnts (vlax-variant-value intPnts))
(if (/= (vlax-safearray-get-u-bound intPnts 1) -1)
(progn
(setq rawPoints (vlax-safearray->list intPnts)
coordInc 0
coordLen (length rawPoints)
intPnts '()
);setq

(while (< coordInc (- coordLen 2))
(setq intPnts (append intPnts (list (list (nth coordInc rawPoints) (nth (1+ coordInc) rawPoints))))
coordInc (+ coordInc 3)
);setq
);while

intPnts
);progn
nil
);if
);defun

[_gile]

Hi,

The LISP code you posted works if the polylines 3d (or whatever kind of curves) do intersect.

Are you sure the polyline 3d you use for testing are truely intersecting?

[nagamalliv]

In top view 3d polylines intersecting.

[_gile · Accepted solution]

IntersectWith method do not return projected intersections.

If you want to get projected intersections, you have to "project" the polyline 3d segment onto the XY plane (i.e. convert 3d points into 2d points) before looking for intersections.

Here's an AutoLISP example:

(defun GetProjectIntersection (sourceName destName /
                               ;; sub functions
                               getProjectVertices getProjectedSegments
                               ;; local variables
                               sourceSegments destSegments intersPoint intersPoints)

  (defun getVertices (poly3d / elst points)
    (setq elst (entget (entnext poly3d)))
    (while (= "VERTEX" (cdr (assoc 0 elst)))
      (setq points  (cons (cdr (assoc 10 elst)) points)
            elst (entget (entnext (cdr (assoc -1 elst))))
      )
    )
    (reverse points)
  )

  (defun getProjectedSegments (vertices)
    (mapcar
      '(lambda (p1 p2)
         (list (list (car p1) (cadr p1)) (list (car p2) (cadr p2)))
       )
      vertices
      (cdr vertices)
    )
  )

  (setq sourceSegments (getProjectedSegments (getVertices sourceName))
        destSegments   (getProjectedSegments (getVertices destName))
  )
  (foreach sourceSegment sourceSegments
    (foreach destSegment destSegments
      (if (setq intersPoint
                 (inters (car sourceSegment)
                         (cadr sourceSegment)
                         (car destSegment)
                         (cadr destSegment)
                 )
          )
        (setq intersPoints (cons intersPoint intersPoints))
      )
    )
  )
  (reverse intersPoints)
)

[nagamalliv]

Working,Thank you so much Gilles Chanteau.

[nagamalliv]

Now i have another problem with vlax-curve-getclosestpointto function not working for 3d polyline

[_gile · Accepted solution]

If vlax-curve-getclosestpointto function doen't work as you expect (IMO, it works as described in the documentation), you can have a look to vlax-curveGetClosestPointToProjection as it seems to me you need 2d behavior with a 3d entity.

PS: you should have posted in the LISP forum.