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ArcGIS Runtime SDK for .NET

Perform spatial operations

This code sample is available for these platforms:
View Sample on GitHub

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

Image of perform spatial operations

Use case

The different spatial operations (union, difference, symmetric difference, and intersection) can be used for a variety of spatial analyses. For example, government authorities may use the intersect operation to determine whether a proposed road cuts through a restricted piece of land such as a nature reserve or a private property. When these operations are chained together, they become even more powerful. An analysis of food deserts within an urban area might begin by union-ing service areas of grocery stores, farmer's markets, and food co-ops. Taking the difference between this single geometry of all services areas and that of a polygon delineating a neighborhood would reveal the areas within that neighborhood where access to healthy, whole foods may not exist.

How to use the sample

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.

How it works

  1. Create a GraphicsOverlay and add it to the MapView.
  2. Define a PointCollection of each Geometry.
  3. Add the overlapping polygons to the graphics overlay.
  4. Perform spatial relationships between the polygons by using the appropriate operation:
    • GeometryEngine.Union(geometry1, geometry2) - This method returns the two geometries united together as one geometry.
    • GeometryEngine.Difference(geometry1, geometry2) - This method returns any part of Geometry2 that does not intersect Geometry1.
    • GeometryEngine.SymmetricDifference(geometry1, geometry2) - This method returns any part of Geometry1 or Geometry2 which do not intersect.
    • GeometryEngine.Intersection(geometry1, geometry2) - This method returns the intersection of Geometry1 and Geometry2.
  5. Use the geometry that is returned from the method call to create a new Graphic and add it to the graphics overlay for it to be displayed.

Relevant API

  • Geometry
  • GeometryEngine
  • GeometryEngine.Difference
  • GeometryEngine.Intersection
  • GeometryEngine.SymmetricDifference
  • GeometryEngine.Union
  • Graphic
  • GraphicsOverlay

Tags

analysis, combine, difference, geometry, intersection, merge, polygon, union

Sample Code

<UserControl 
    x:Class="ArcGISRuntime.UWP.Samples.SpatialOperations.SpatialOperations"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:esriUI="using:Esri.ArcGISRuntime.UI.Controls">
    <Grid>
        <esriUI:MapView x:Name="MyMapView" />
        <Border Background="White" BorderBrush="Black" BorderThickness="1"
                HorizontalAlignment="Center" VerticalAlignment="Top"
                Margin="30" Padding="10" Width="275">
            <StackPanel>
                <TextBlock Text="Select a spatial operation:"/>
                <ComboBox x:Name="SpatialOperationComboBox" 
                          Margin="0,5"
                          SelectionChanged="SpatialOperationComboBox_SelectionChanged" Width="253"/>
                <Button x:Name="ResetOperationButton"
                        Content="Reset operation"
                        Click="ResetOperationButton_Click" Width="253"/>
            </StackPanel>
        </Border>
    </Grid>
</UserControl>
// 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 Windows.UI.Xaml;

namespace ArcGISRuntime.UWP.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, Windows.UI.Xaml.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);
        }
    }
}