Spatial relationships

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Determine spatial relationships between two geometries.

Image of spatial relationships

Use case

In case of a natural disaster, emergency services can represent the affected areas using polygons. By determining the spatial relationships between these and any other existing features such as populated areas, infrastructure, or natural resources, it is possible to quickly determine which of the existing features might be affected or is in further danger, helping to assess risk and define further action.

How to use the sample

Select one of the three graphics. The tree view will list the relationships the selected graphic has to the other graphic geometries.

How it works

  1. Get the geometry from two different graphics. In this example the geometry of the selected graphic is compared to the geometry of each unselected graphic.
  2. Use the methods in GeometryEngine to check the relationship between the geometries, e.g. contains, disjoint, intersects, etc. If the method returns true, the relationship exists.

Relevant API

  • Geometry
  • GeometryEngine
  • GeometryEngine.Contains
  • GeometryEngine.Crosses
  • GeometryEngine.Disjoint
  • GeometryEngine.Intersects
  • GeometryEngine.Overlaps
  • GeometryEngine.Touches
  • GeometryEngine.Within
  • GeometryType
  • Graphic
  • Point
  • Polygon
  • Polyline

Tags

geometries, relationship, spatial analysis

Sample Code

SpatialRelationships.cs
                                                                                                                                                                                                                                                
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// 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 System;
using Android.App;
using Android.OS;
using Android.Views;
using Android.Widget;
using Esri.ArcGISRuntime.Data;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI;
using Esri.ArcGISRuntime.UI.Controls;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;

namespace ArcGISRuntime.Samples.SpatialRelationships
{
    [Activity (ConfigurationChanges=Android.Content.PM.ConfigChanges.Orientation | Android.Content.PM.ConfigChanges.ScreenSize)]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Spatial relationships",
        category: "Geometry",
        description: "Determine spatial relationships between two geometries.",
        instructions: "Select one of the three graphics. The tree view will list the relationships the selected graphic has to the other graphic geometries.",
        tags: new[] { "geometries", "relationship", "spatial analysis" })]
    public class SpatialRelationships : Activity
    {
        private TextView _resultTextView;
        private MapView _myMapView;

        // References to the graphics and graphics overlay
        private GraphicsOverlay _graphicsOverlay;

        private Graphic _polygonGraphic;
        private Graphic _polylineGraphic;
        private Graphic _pointGraphic;

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            Title = "Spatial relationships";

            CreateLayout();
            Initialize();
        }

        private void Initialize()
        {
            // Configure the basemap
            _myMapView.Map = new Map(BasemapStyle.ArcGISTopographic);

            // Create the graphics overlay
            _graphicsOverlay = new GraphicsOverlay();

            // Add the overlay to the MapView
            _myMapView.GraphicsOverlays.Add(_graphicsOverlay);

            // Update the selection color
            _myMapView.SelectionProperties.Color = Color.Yellow;

            // Create the point collection that defines the polygon
            PointCollection polygonPoints = new PointCollection(SpatialReferences.WebMercator)
            {
                new MapPoint(-5991501.677830, 5599295.131468),
                new MapPoint(-6928550.398185, 2087936.739807),
                new MapPoint(-3149463.800709, 1840803.011362),
                new MapPoint(-1563689.043184, 3714900.452072),
                new MapPoint(-3180355.516764, 5619889.608838)
            };

            // Create the polygon
            Polygon polygonGeometry = new Polygon(polygonPoints);

            // Define the symbology of the polygon
            SimpleLineSymbol polygonOutlineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, System.Drawing.Color.Green, 2);
            SimpleFillSymbol polygonFillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle.ForwardDiagonal, System.Drawing.Color.Green, polygonOutlineSymbol);

            // Create the polygon graphic and add it to the graphics overlay
            _polygonGraphic = new Graphic(polygonGeometry, polygonFillSymbol);
            _graphicsOverlay.Graphics.Add(_polygonGraphic);

            // Create the point collection that defines the polyline
            PointCollection polylinePoints = new PointCollection(SpatialReferences.WebMercator)
            {
                new MapPoint(-4354240.726880, -609939.795721),
                new MapPoint(-3427489.245210, 2139422.933233),
                new MapPoint(-2109442.693501, 4301843.057130),
                new MapPoint(-1810822.771630, 7205664.366363)
            };

            // Create the polyline
            Polyline polylineGeometry = new Polyline(polylinePoints);

            // Create the polyline graphic and add it to the graphics overlay
            _polylineGraphic = new Graphic(polylineGeometry, new SimpleLineSymbol(SimpleLineSymbolStyle.Dash, System.Drawing.Color.Red, 4));
            _graphicsOverlay.Graphics.Add(_polylineGraphic);

            // Create the point geometry that defines the point graphic
            MapPoint pointGeometry = new MapPoint(-4487263.495911, 3699176.480377, SpatialReferences.WebMercator);

            // Define the symbology for the point
            SimpleMarkerSymbol locationMarker = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle.Circle, System.Drawing.Color.Blue, 10);

            // Create the point graphic and add it to the graphics overlay
            _pointGraphic = new Graphic(pointGeometry, locationMarker);
            _graphicsOverlay.Graphics.Add(_pointGraphic);

            // Listen for taps; the spatial relationships will be updated in the handler
            _myMapView.GeoViewTapped += myMapView_GeoViewTapped;

            // Set the viewpoint to center on the point
            _myMapView.SetViewpointGeometryAsync(GeometryEngine.Union(polygonGeometry, polylineGeometry), 50);
        }

        private async void myMapView_GeoViewTapped(object sender, GeoViewInputEventArgs e)
        {
            // Identify the tapped graphics
            IdentifyGraphicsOverlayResult result = null;

            try
            {
                result = await _myMapView.IdentifyGraphicsOverlayAsync(_graphicsOverlay, e.Position, 1, false);
            }
            catch (Exception ex)
            {
                new AlertDialog.Builder(this).SetMessage(ex.ToString()).SetTitle("Error").Show();
            }

            // Return if there are no results
            if (result == null || result.Graphics.Count < 1)
            {
                return;
            }

            // Get the first identified graphic
            Graphic identifiedGraphic = result.Graphics.First();

            // Clear any existing selection, then select the tapped graphic
            _graphicsOverlay.ClearSelection();
            identifiedGraphic.IsSelected = true;

            // Get the selected graphic's geometry
            Geometry selectedGeometry = identifiedGraphic.Geometry;

            // Perform the calculation and show the results
            _resultTextView.Text = GetOutputText(selectedGeometry);
        }

        private string GetOutputText(Geometry selectedGeometry)
        {
            string output = $"Selected: {selectedGeometry.GeometryType}\n";

            // Get the relationships
            List<SpatialRelationship> polygonRelationships = GetSpatialRelationships(selectedGeometry, _polygonGraphic.Geometry);
            List<SpatialRelationship> polylineRelationships = GetSpatialRelationships(selectedGeometry, _polylineGraphic.Geometry);
            List<SpatialRelationship> pointRelationships = GetSpatialRelationships(selectedGeometry, _pointGraphic.Geometry);

            // Add the point relationships to the output
            if (selectedGeometry.GeometryType != GeometryType.Point)
            {
                output += "    Relationship(s) with Point:\n";
                foreach (SpatialRelationship relationship in pointRelationships)
                {
                    output += $"        {relationship}\n";
                }
            }
            // Add the polygon relationships to the output
            if (selectedGeometry.GeometryType != GeometryType.Polygon)
            {
                output += "    Relationship(s) with Polygon:\n";
                foreach (SpatialRelationship relationship in polygonRelationships)
                {
                    output += $"        {relationship}\n";
                }
            }
            // Add the polyline relationships to the output
            if (selectedGeometry.GeometryType != GeometryType.Polyline)
            {
                output += "    Relationship(s) with Polyline:\n";
                foreach (SpatialRelationship relationship in polylineRelationships)
                {
                    output += $"        {relationship}\n";
                }
            }

            return output.TrimEnd('\n');
        }

        /// <summary>
        /// Returns a list of spatial relationships between two geometries
        /// </summary>
        /// <param name="a">The 'a' in "a contains b"</param>
        /// <param name="b">The 'b' in "a contains b"</param>
        /// <returns>A list of spatial relationships that are true for a and b.</returns>
        private static List<SpatialRelationship> GetSpatialRelationships(Geometry a, Geometry b)
        {
            List<SpatialRelationship> relationships = new List<SpatialRelationship>();
            if (GeometryEngine.Crosses(a, b)) { relationships.Add(SpatialRelationship.Crosses); }
            if (GeometryEngine.Contains(a, b)) { relationships.Add(SpatialRelationship.Contains); }
            if (GeometryEngine.Disjoint(a, b)) { relationships.Add(SpatialRelationship.Disjoint); }
            if (GeometryEngine.Intersects(a, b)) { relationships.Add(SpatialRelationship.Intersects); }
            if (GeometryEngine.Overlaps(a, b)) { relationships.Add(SpatialRelationship.Overlaps); }
            if (GeometryEngine.Touches(a, b)) { relationships.Add(SpatialRelationship.Touches); }
            if (GeometryEngine.Within(a, b)) { relationships.Add(SpatialRelationship.Within); }
            return relationships;
        }

        private void CreateLayout()
        {
            // Create a new vertical layout for the app
            LinearLayout layout = new LinearLayout(this) { Orientation = Orientation.Vertical };

            // Create a help label for the sample.
            TextView helpLabel = new TextView(this) { Gravity = GravityFlags.Center };
            helpLabel.Text = "Tap a graphic to select it. The display will update to show the relationships with the other graphics.";

            // Create a Textview for the results.
            _resultTextView = new TextView(this);
            _resultTextView.SetMinLines(7);

            //Add the labels to the layout.
            layout.AddView(helpLabel);
            layout.AddView(_resultTextView);
            _myMapView = new MapView(this);
            layout.AddView(_myMapView);

            // Show the layout in the app.
            SetContentView(layout);
        }
    }
}

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