Topic: How to IntersectWith() for multiple selections

[nobody]

I don't know why I can't wrap my head around this but I need to find the intersections of multiple selected polylines crossing each other and get their coordinates.  Anyone have anything they'd be willing to share that might help? If not no biggy.  Thanks!

[ronjonp]

Here's a quick one .. does not include self intersecting polylines.

Code - Auto/Visual Lisp: [Select]

1. (defun _intersections (/ e out p ss x)
2.   (if (setq ss (ssget "_x" (list (cons 0 "*LINE,ARC,CIRCLE,ELLIPSE"))))
3.     (progn (setq ss (mapcar 'vlax-ename->vla-object (mapcar 'cadr (ssnamex ss))))
4.            (while (setq e (car ss))
5.              (if (setq p
6.                         (apply 'append
7.                                (vl-remove 'nil
8.                                           (mapcar '(lambda (x) (vlax-invoke e "intersectwith" x acextendnone))
9.                                                   (setq ss (cdr ss))
10.                                           )
11.                                )
12.                         )
13.                  )
14.                (while p (setq out (cons (list (car p) (cadr p) (caddr p)) out)) (setq p (cdddr p)))
15.              )
16.            )
17.     )
18.   )
19.   out
20. )
21. (_intersections)

[nobody]

If only i was using lisp  

[ronjonp]

If only i was using lisp

DOH! Wrong forum

[Jeff_M]

May be better ways of doing this, but it seems to have worked for me when needed.

Code - C#: [Select]

1.         [CommandMethod("PolyIntersect")]
2.         public void polyintersects()
3.         {
4.             Document doc = Application.DocumentManager.MdiActiveDocument;
5.             Editor ed  = doc.Editor;
6.             Database db = doc.Database;
7.             PromptSelectionOptions ssOpts = new PromptSelectionOptions();
8.             ssOpts.MessageForAdding = "Select polylines:";
9.             ssOpts.MessageForRemoval = "...Select polylines to remove from selection:";
10.             ssOpts.RejectObjectsOnLockedLayers = true;
11.             TypedValue[] tv = { new TypedValue(0, "LWPOLYLINE") };
12.             SelectionFilter filter = new SelectionFilter(tv);
13.             PromptSelectionResult ssRes = ed.GetSelection(ssOpts, filter);
14.             if (ssRes.Status != PromptStatus.OK)
15.                 return;
16.             using (Transaction tr = db.TransactionManager.StartTransaction())
17.             {
18.                 Point3dCollection interPoints = getintersectingpoints(ssRes.Value.GetObjectIds());
19.                 //do what you need with the points here
20.                 ed.WriteMessage("\nFound {0} instersections", interPoints.Count.ToString());
21.                 tr.Commit();
22.             }
23.         }
24.  
25.         private Point3dCollection getintersectingpoints(ObjectId[] idArray)
26.         {
27.             List<ObjectId> ids = idArray.ToList<ObjectId>();          
28.             List<ObjectId> idstocompare = idArray.ToList<ObjectId>();
29.             idstocompare.RemoveAt(0);
30.             Point3dCollection intersectpoints = new Point3dCollection();
31.             for (int i = 0; i < ids.Count - 1; i++)
32.             {
33.                 Polyline poly = (Polyline)ids[i].GetObject(OpenMode.ForRead);
34.                 foreach (ObjectId id in idstocompare)
35.                 {
36.                     Polyline poly2 = (Polyline)id.GetObject(OpenMode.ForRead);
37.                     Point3dCollection points = new Point3dCollection();
38.                     poly.IntersectWith(poly2, Intersect.ExtendArgument, points, new IntPtr(0), new IntPtr(0));
39.                     foreach (Point3d pt in points)
40.                     {
41.                         if (!intersectpoints.Contains(pt))
42.                             intersectpoints.Add(pt);
43.                     }
44.                 }
45.                 idstocompare.RemoveAt(0);
46.             }
47.             return intersectpoints;
48.         }
49.     }
50.  

[nobody]

Thank you jeff   /kowtow