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GeometryEngineUnion Method (Geometry, Geometry)

The union operation constructs the set-theoretic union of the geometries in the input array.

Namespace:  Esri.ArcGISRuntime.Geometry
Assembly:  Esri.ArcGISRuntime (in Esri.ArcGISRuntime.dll) Version: 100.9.0
Syntax
public static Geometry Union(
	Geometry geometry1,
	Geometry geometry2
)

Parameters

geometry1
Type: Esri.ArcGISRuntime.GeometryGeometry
The first geometry to union with.
geometry2
Type: Esri.ArcGISRuntime.GeometryGeometry
The second geometry to union with.

Return Value

Type: Geometry
The unioned geometry.
Remarks

GeometryEngine.Union returns all parts of the two input geometries combined into a single geometry. This means that the order of the input parameters of the GeometryEngine.Intersection is irrelevant. In a theoretical variable format you can think of the GeometryEngine.Union equation like:
A (Union) B = C
B (Union) A = C

The following is a visual illustration of two polygon geometries and how the output result would be from the GeometryEngine.Union operation:

GeometryEngine.Union visual examples.

Examples

WPF

Example Name: SpatialOperations

Find the union, intersection, or difference of two geometries.

Code example screen shot.

C#
// Copyright 2018 Esri.
// 
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.
// You may obtain a copy of the License at: http://www.apache.org/licenses/LICENSE-2.0
// 
// Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific
// language governing permissions and limitations under the License.

using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI;
using System.Collections.Generic;
using System.Windows;

namespace ArcGISRuntime.WPF.Samples.SpatialOperations
{
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Perform spatial operations",
        category: "Geometry",
        description: "Find the union, intersection, or difference of two geometries.",
        instructions: "The sample provides an option to select a spatial operation. When an operation is selected, the resulting geometry is shown in red. The 'reset operation' button undoes the action and allow selecting a different operation.",
        tags: new[] { "analysis", "combine", "difference", "geometry", "intersection", "merge", "polygon", "union" })]
    public partial class SpatialOperations
    {
        // GraphicsOverlay to hold the polygon graphics.
        private GraphicsOverlay _polygonsOverlay;

        // Polygon graphics to run spatial operations on.
        private Graphic _graphicOne;
        private Graphic _graphicTwo;

        // Graphic to display the spatial operation result polygon.
        private Graphic _resultGraphic;

        public SpatialOperations()
        {
            InitializeComponent();

            // Create the map, set the initial extent, and add the polygon graphics.
            Initialize();
        }

        private void Initialize()
        {
            // Create the map with a gray canvas basemap and an initial location centered on London, UK.
            Map spatialOperationsMap = new Map(BasemapType.LightGrayCanvas, 51.5017, -0.12714, 15);

            // Add the map to the map view.
            MyMapView.Map = spatialOperationsMap;

            // Create and add two overlapping polygon graphics to operate on.
            CreatePolygonsOverlay();

            // Fill the combo box with some spatial operations to run on the polygon graphics.
            SpatialOperationComboBox.Items.Add("Difference");
            SpatialOperationComboBox.Items.Add("Intersection");
            SpatialOperationComboBox.Items.Add("Symmetric difference");
            SpatialOperationComboBox.Items.Add("Union");
        }

        // Handle the spatial operation selection by performing the operation and showing the result polygon.
        private void SpatialOperationComboBox_SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
        {
            // If an operation hasn't been selected, return.
            if (SpatialOperationComboBox.SelectedItem == null) { return; }

            // Remove any currently displayed result.
            _polygonsOverlay.Graphics.Remove(_resultGraphic);

            // Polygon geometry from the input graphics.
            Geometry polygonOne = _graphicOne.Geometry;
            Geometry polygonTwo = _graphicTwo.Geometry;

            // Result polygon for spatial operations.
            Geometry resultPolygon = null;

            // Run the selected spatial operation on the polygon graphics and get the result geometry.
            string operation = (string)SpatialOperationComboBox.SelectedItem;
            switch (operation)
            {
                case "Union":
                    resultPolygon = GeometryEngine.Union(polygonOne, polygonTwo);
                    break;
                case "Difference":
                    resultPolygon = GeometryEngine.Difference(polygonOne, polygonTwo);
                    break;
                case "Symmetric difference":
                    resultPolygon = GeometryEngine.SymmetricDifference(polygonOne, polygonTwo);
                    break;
                case "Intersection":
                    resultPolygon = GeometryEngine.Intersection(polygonOne, polygonTwo);
                    break;
            }

            // Create a black outline symbol to use for the result polygon.
            SimpleLineSymbol outlineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, System.Drawing.Color.Black, 1);

            // Create a solid red fill symbol for the result polygon graphic.
            SimpleFillSymbol resultSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle.Solid, System.Drawing.Color.Red, outlineSymbol);

            // Create the result polygon graphic and add it to the graphics overlay.
            _resultGraphic = new Graphic(resultPolygon, resultSymbol);
            _polygonsOverlay.Graphics.Add(_resultGraphic);
        }

        private void ResetOperationButton_Click(object sender, RoutedEventArgs e)
        {
            // Remove any currently displayed result.
            _polygonsOverlay.Graphics.Remove(_resultGraphic);

            // Clear the selected spatial operation.
            SpatialOperationComboBox.SelectedIndex = -1;
        }

        private void CreatePolygonsOverlay()
        {
            // Create a black outline symbol to use for the polygons.
            SimpleLineSymbol outlineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, System.Drawing.Color.Black, 1);

            // Create a point collection to define polygon vertices.
            PointCollection polygonVertices = new PointCollection(SpatialReferences.WebMercator)
            {
                new MapPoint(-13960, 6709400),
                new MapPoint(-14660, 6710000),
                new MapPoint(-13760, 6710730),
                new MapPoint(-13300, 6710500),
                new MapPoint(-13160, 6710100)
            };

            // Create a polygon graphic with a blue fill.
            SimpleFillSymbol fillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle.Vertical, System.Drawing.Color.Blue, outlineSymbol);
            Polygon polygonOne = new Polygon(polygonVertices);
            _graphicOne = new Graphic(polygonOne, fillSymbol);

            // Create a point collection to define outer polygon ring vertices.
            PointCollection outerRingVerticesCollection = new PointCollection(SpatialReferences.WebMercator)
            {
                new MapPoint(-13060, 6711030),
                new MapPoint(-12160, 6710730),
                new MapPoint(-13160, 6709700),
                new MapPoint(-14560, 6710730)
            };

            // Create a point collection to define inner polygon ring vertices ("donut hole").
            PointCollection innerRingVerticesCollection = new PointCollection(SpatialReferences.WebMercator)
            {
                new MapPoint(-13060, 6710910),
                new MapPoint(-14160, 6710630),
                new MapPoint(-13160, 6709900),
                new MapPoint(-12450, 6710660)
            };

            // Create a list to contain the inner and outer ring point collections.
            List<PointCollection> polygonParts = new List<PointCollection>
            {
                outerRingVerticesCollection,
                innerRingVerticesCollection
            };

            // Create a polygon graphic with a green fill.
            fillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle.Horizontal, System.Drawing.Color.Green, outlineSymbol);
            _graphicTwo = new Graphic(new Polygon(polygonParts), fillSymbol);

            // Create a graphics overlay in the map view to hold the polygons.
            _polygonsOverlay = new GraphicsOverlay();
            MyMapView.GraphicsOverlays.Add(_polygonsOverlay);

            // Add the polygons to the graphics overlay.
            _polygonsOverlay.Graphics.Add(_graphicOne);
            _polygonsOverlay.Graphics.Add(_graphicTwo);
        }
    }
}
XAML
<UserControl
    x:Class="ArcGISRuntime.WPF.Samples.SpatialOperations.SpatialOperations"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:esri="http://schemas.esri.com/arcgis/runtime/2013">
    <Grid>
        <esri:MapView x:Name="MyMapView" />
        <Border Style="{StaticResource BorderStyle}">
            <StackPanel>
                <TextBlock Margin="5" Text="Select a spatial operation:" />
                <ComboBox
                    x:Name="SpatialOperationComboBox"
                    Margin="5"
                    SelectionChanged="SpatialOperationComboBox_SelectionChanged" />
                <Button
                    x:Name="ResetOperationButton"
                    Margin="5"
                    Click="ResetOperationButton_Click"
                    Content="Reset operation" />
            </StackPanel>
        </Border>
    </Grid>
</UserControl>
See Also
Additional Examples
Hyperlink to ExampleDescription
SpatialOperationsFind the union, intersection, or difference of two geometries.