Nice find!
I was going to say to reverse the polyline and check the paramatpoint again, but the code you found seems to work great.

Thanks.

Yes, your code helps if I want to find the intersection point(s). Note: I also have that code and use it often for other purposes but my questions is how can I find its stations/distance from the beginning of polyline. My Task: I need to mark the stations on a profile and my code will only provide the shortest station only.

Here is some code to get a list of intersections.
These are the locations you need to add the extra number.
Hope it's helpful!

Code - Auto/Visual Lisp: [Select]

1. ;|
2. ; Get Intersections - dexus
3. ; Returns a list of intersecting points in a polyline
4. ; @Param poly Ename or vla-object of polyline
5. ; @Returns List of intersecting points
6. |;
7. (defun getIntersections (poly / cords)
8.   (if
9.     (and
10.       (setq poly ; Get (list ename vla-object) of selected object
11.         (cond
12.            ((= (type poly) 'vla-object) (list (vlax-vla-object->ename poly) poly))
13.            ((= (type poly) 'ename) (list poly (vlax-ename->vla-object poly)))
14.         )
15.       )
16.       (vl-position (cdr (assoc 0 (entget (car poly)))) '("POLYLINE" "LWPOLYLINE"))
17.       (setq cords (getcoords (car poly)))
18.     )
19.     (vl-remove-if ; Return list of intersections
20.       (function (lambda (i) (vl-member-if (function (lambda (cord) (equal cord i 1e-9))) cords))) ; Remove coordinates (vertices)
21.       (LM:group-n (gc:VariantToLispData (vla-intersectwith (cadr poly) (cadr poly) acExtendNone)) 3) ; Get all intersections
22.     )
23.   )
24. )
25.  
26. ;; CAB 08/25/06 - revised 07.25.07
27. ;; get pline vertex list for any
28. (defun getcoords (ent / endp idx pt result)
29.   (setq idx 0
30.         endp (vlax-curve-getEndParam ent))
31.   (while (< (setq idx (1+ idx)) endp)
32.     (setq pt (vlax-curve-getpointatparam ent idx)
33.           result (cons pt result))
34.   )
35.   (reverse (cons (vlax-curve-getendpoint ent) result))
36. )
37.  
38. ;; gc:VariantToLispData - gile
39. ;; Converts a variant or a safearray into an AutoLISP data
40. ;; input var = variant or safearray
41. (defun gc:VariantToLispData (var)
42.   (cond
43.     ((= (type var) 'variant)
44.       (gc:VariantToLispData (vlax-variant-value var)))
45.     ((= (type var) 'safearray)
46.       (if (< -1 (vlax-safearray-get-u-bound var 1))
47.         (mapcar 'gc:VariantToLispData (vlax-safearray->list var))
48.       )
49.     )
50.     (t var)
51.   )
52. )
53.  
54. ;; Group by Number  -  Lee Mac
55. ;; Groups a list 'l' into a list of lists, each of length 'n'
56. (defun LM:group-n ( l n / r )
57.     (if l
58.         (cons
59.             (reverse (repeat n (setq r (cons (car l) r) l (cdr l)) r))
60.             (LM:group-n l n)
61.         )
62.     )
63. )

If an alignment is a self intersecting polyline, how can I get the 2 stations number at the point of intersection?
Picture bellow will give a better explanation.

Note: My code will only get the first station number:

(defun c:Foo ()

  (vl-load-com)
  (setq obj (vlax-ename->vla-object (car (entsel "\n. Select an alignment:"))))
  (while (setq pt  (getpoint "\n. Select point at Alignment: \n"))
    (setq ptis  (vlax-curve-getClosestPointTo obj (vlax-curve-getClosestPointTo obj pt T) T))
    (setq stais (vlax-curve-getDistAtPoint obj ptis))
    (princ (strcat "\n. STA = " (rtos stais 2 3)))
   );end of while
   (princ)
)


...

Verry intresting topic.

I took some code from it to build my own solution to add multiple breaklines:

SelectionSet res = getSelectionSet();
if (res != null)
{
    PromptKeywordOptions pKeyOpts = new PromptKeywordOptions("");
    pKeyOpts.Message = "\nEnter the type of breakline to create: ";
    pKeyOpts.Keywords.Add("Standard");
    pKeyOpts.Keywords.Add("Non-Destructive");
    pKeyOpts.Keywords.Add("Proximity");
    pKeyOpts.Keywords.Default = "Standard";
    pKeyOpts.AllowNone = true;
    PromptResult pKeyRes = editor.GetKeywords(pKeyOpts);
    ObjectId[] lines;

    try
    {
        switch (pKeyRes.StringResult)
        {
            case "Non-Destructive":

                // Step through the objects in the selection set
                foreach (ObjectId acSSObj in res.GetObjectIds())
                {
                    lines = new ObjectId[] { acSSObj };
                    oSurface.BreaklinesDefinition.AddNonDestructiveBreaklines(new ObjectIdCollection(lines), 1);
                }
                break;
            case "Proximity":

                // Step through the objects in the selection set
                foreach (ObjectId acSSObj in res.GetObjectIds())
                {
                    lines = new ObjectId[] { acSSObj };
                    oSurface.BreaklinesDefinition.AddProximityBreaklines(new ObjectIdCollection(lines), 1);
                }
                break;
            case "Standard":
            default:
                // Step through the objects in the selection set
                foreach (ObjectId acSSObj in res.GetObjectIds())
                {
                    lines = new ObjectId[] { acSSObj };
                    //oSurface.BreaklinesDefinition.AddStandardBreaklines(new ObjectIdCollection(lines), 10, 5, 5, 0);
                    oSurface.BreaklinesDefinition.AddStandardBreaklines(new ObjectIdCollection(lines), 0.01, 2, 5, 0);
                }
                break;
        }
    }

    catch (System.Exception e)
    {
        editor.WriteMessage("Operation failed: {0}", e.Message);
    }

    // commit the transaction
    ts.Commit();
}public SelectionSet getSelectionSet()
{
    //CivilDocument doc = Autodesk.Civil.ApplicationServices.CivilApplication.ActiveDocument;
    Editor ed = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument.Editor;

    // Request for objects to be selected in the drawing area
    PromptSelectionResult acSSPrompt = ed.GetSelection();

    // If the prompt status is OK, objects were selected
    if (acSSPrompt.Status == PromptStatus.OK)
    {
        SelectionSet acSSet = acSSPrompt.Value;
        return acSSet;

    }
    return null;
}

Efficiency test, 510 entities, including 505 duplicate entities

Hash table efficiency far exceeds overkill

 

===============================

Command: tt
Select objects: Specify opposite corner: 510 found

Select objects:

===============================

Command: (tt1)

CPU:(1x)Intel(R) Xeon(R) E3-1575M v5 @ 3.00GHz 4Cores  / Memory:64G / OS: WIN10 professional workstation version
Benchmarking ......
Current settings: Tolerance=0.000001, Ignore=None, Optimize polylines=Yes, Combine partial overlap=Yes, Combine end-to-end=Yes
505 duplicate(s) deleted
0 overlapping object(s) or segment(s) deleted. done for 16 iterations. Sorted from fastest.
Statement                    Increment  Time(ms)  Normalize  Relative
-------------------------------------------------------------------------------
(xdrx-entity-removeduplic...)       16      1078         1078     28.07 <fastest>
(COMMAND ._-overkill SS  )          1       1891      30256       1.00 <slowest>
-------------------------------------------------------------------------------