[GIS] How to find self-intersecting polylines using ArcObjects

arcobjectsgeometrytopology

If I have a polyline, how do I figure out whether it is self-intersecting? I tried to use ITopologicalOperator.IsSimple Property, but it always returns true.

Are there any ways of doing these kind of topological checks over individual geometries?

Best Answer

I think you can do with with the ITopologicalOperator2 interface:

dim pTopoLogicalOp as ITopologicalOperator2
Set pPolyline = pFeature.ShapeCopy
Set pTopoLogicalOp = pPolyline
Let pTopoLogicalOp.IsKnownSimple = False
If pTopoLogicalOp.IsSimple = False Then
   ' Polyline is self intersecting
End If

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[GIS] Deriving separate polylines from coded points using ArcObjects (Figure inside)

Not to be meant as a serious complete answer, but rather just an idea to toss around - I wonder if Thiessen polygons could perhaps be of any use in this case.

Points broken down into Thiessen polygons

Now, the trick is to find a reliable algorithm to identify those polygon boundary segments which form the centerline. Once you have the centerline, it is easy to decide on which side a point lies. Any ideas?

As a side note: I know this should be a comment, not an answer, but since you cannot post uploaded images in comments, I figured I'd dare to make an exception.

[GIS] Intersecting two polylines using ArcObjects

Use the return value of the Intersect method instead of the TopologicalOperator. Try the following instead (I use C#, not VB.NET, so hopefully this works. The casting business is really confusing):

Dim topoOp As ITopologicalOperator = TryCast(pTestPoly2, ITopologicalOperator)
Dim pOutPointCol As IPointCollection = TryCast(topoOp.Intersect(TryCast(pTestPoly1, IGeometry), ESRI.ArcGIS.Geometry.esriGeometryDimension.esriGeometry0Dimension), IPointCollection)

Best Answer

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[GIS] Deriving separate polylines from coded points using ArcObjects (Figure inside)

[GIS] Intersecting two polylines using ArcObjects

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