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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.

screenshot

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(
        "Spatial operations",
        "Geometry",
        "Demonstrates how to use the GeometryEngine to perform geometry operations between overlapping polygons in a GraphicsOverlay.",
        "The sample provides a drop down on the top, where you can select a geometry operation. When you choose a geometry operation, the application performs this operation between the overlapping polygons and applies the result to the geometries.")]
    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);
        }
    }
}