how to split a polyline at its self intersection points
Hi,
Yes, GetSplitCurves() could be useful as it can split the polyline, however you have to provide the additional logic that will be able to turn the polyline you attached into 3 closed loop polylines. Depending on which vertex is the start/end point of the polyline you'll get different results.
Another thing that might be useful for you to know is that there is a boundary tracing function available since AutoCAD 2011. In AutoCAD 2011 only in the ARX API (I think), but in 2012 it is also available under Editor.TraceBoundary(). If you specify a point that fals inside a loop then it will give you the poly loop around that point. In previous versions you could use the -BOUNDARY command instead.
In both cases though first you'd probably have to figure out the intersection points. So you would need to iterate through each segment of the poly and try to intersect it with all the other segments. Depending on the return value of Polyline.GetSegmentType() you would need to call either GetLineSegmentAt or GetArcSegmentAt. These segments then provide an IntersectWith function that you can use.
I hope this helps.
Cheers,
Adam Nagy
Autodesk Developer Network
Adam Nagy
Autodesk Platform Services
Simplified version, not tested for special types of intersections.
After splitting Create Region is added to show results.
[CommandMethod("SPAI")]
public static void SplitPolylineAtIntersection()
{
Document doc = null;
Database db = null;
Editor ed = null;
try
{
doc = AcadApp.DocumentManager.MdiActiveDocument;
if (doc == null)
throw new System.Exception("No MdiActiveDocument");
db = doc.Database;
ed = doc.Editor;
var plPeo = new PromptEntityOptions("Select Poly");
var per = ed.GetEntity(plPeo);
if (per.Status != PromptStatus.OK)
return;
var plId = per.ObjectId;
using (Transaction tr = db.TransactionManager.StartTransaction())
{
var ms = (BlockTableRecord)tr.GetObject(SymbolUtilityServices.GetBlockModelSpaceId(db), OpenMode.ForWrite);
var pl = tr.GetObject(plId, OpenMode.ForRead) as Polyline;
var plSegs = new DBObjectCollection();
pl.Explode(plSegs);
//Test each Poly Segment for intersection with the other segments.
//These segments will be splitted at the intersections and tested again
int i = -1;
while (++i < plSegs.Count)
{
var segi = plSegs[i] as Curve;
if (segi == null) continue;
int j = -1;
while (++j < plSegs.Count)
{
if (j == i) continue;
var segj = plSegs[j] as Curve;
if (segj == null) continue;
//Test Segment[i] against Segment[j]
Point3dCollection intsPnts = new Point3dCollection();
segi.IntersectWith(segj, Intersect.OnBothOperands, intsPnts, IntPtr.Zero, IntPtr.Zero);
if (intsPnts.Count > 0)
{
var splCurves = segi.GetSplitCurves(intsPnts);
if (splCurves.Count > 1) //don't add curves splitted at the start or end
{
foreach (DBObject splCurve in splCurves)
{
plSegs.Add(splCurve);
//for testing purposes add segments to database
ms.AppendEntity((Entity)splCurve);
tr.AddNewlyCreatedDBObject(splCurve, true);
}
plSegs[i] = null;
break; //exit while j, next i
}
}
}
}
pl.UpgradeOpen();
pl.Erase();
//for testing purposes add remaning segments to database
// add the not splitted segments to the Database
foreach (DBObject plseg in plSegs)
{
if (plseg == null) continue;
if (plseg.ObjectId.IsNull)
{
ms.AppendEntity((Entity)plseg);
tr.AddNewlyCreatedDBObject(plseg, true);
}
}
//Create regions from splitted segments
// then create closed polylines from these regions
var regions=Region.CreateFromCurves(plSegs);
//for testing purposes add regions to database
foreach (DBObject region in regions)
{
ms.AppendEntity((Entity)region);
tr.AddNewlyCreatedDBObject(region, true);
}
tr.Commit();
}
}
catch (System.Exception ex)
{
if (ed != null)
ed.WriteMessage("\n Error in SplitPolylineAtIntersection: {0}", ex.Message);
}
}
