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ITopologicalOperator.Union Method (ArcObjects .NET 10.7 SDK)
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ITopologicalOperator.Union Method

Constructs the geometry that is the set-theoretic union of the input geometries.

[Visual Basic .NET]
Public Function Union ( _
    ByVal other As IGeometry _
) As IGeometry
public IGeometry Union (
    IGeometry other
  IGeometry* other

other is a parameter of type IGeometry*

Product Availability

Available with ArcGIS Engine, ArcGIS Desktop, and ArcGIS Server.


The Union of two Geometries of the same Dimension is a single Geometry corresponding to the combination of both Geometries such that anything within either of the original geometries is also part of the unioned geometry, but anything common to both geometries only exists once in the unioned geometry.


The Union is basically an OR between the input geometries.

ITopologicalOperator methods must be applied on high-level geometries only. High-Level geometries are point, multipoint, polyline and polygon. To use this method with low-level geometries such as segments (Line, Circular Arc, Elliptic Arc, B├ęzier Curve), paths or rings, they must be wrapped into high-level geometries types.

This method does not support GeometryBags.

Union Example


//The following code shows to wrap a line segment into a polyline in C#

//Assume a line (line1 as ILine) is already created

object obj = Type.Missing;

ISegmentCollection segCollection = new PolylineClass() as ISegmentCollection;

segCollection.AddSegment((ISegment)line1, ref obj, ref obj);

//Set the spatial reference on the new polyline

//The spatial reference is not transfered automatically from the segments

IGeometry geom = segCollection as IGeometry;

geom.SpatialReference = spatialRef;

//Can now be used with ITopologicalOperator methods


See Also

ITopologicalOperator Interface