Find the union, intersection, or difference of two geometries.
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
- Create a
GraphicsOverlay
and add it to theMapView
. - Define a
PointCollection
of eachGeometry
. - Add the overlapping polygons to the graphics overlay.
- 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.
- 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
// 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 System.Collections.Generic;
using System.Drawing;
using ArcGISRuntime;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI;
using Esri.ArcGISRuntime.UI.Controls;
using Foundation;
using UIKit;
namespace ArcGISRuntimeXamarin.Samples.SpatialOperations
{
[Register("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 class SpatialOperations : UIViewController
{
// Hold references to UI controls.
private MapView _myMapView;
private UISegmentedControl _operationChoiceButton;
// 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()
{
Title = "Spatial operations";
}
private void Initialize()
{
// Create and show a map with a gray canvas basemap and an initial location centered on London, UK.
_myMapView.Map = new Map(BasemapStyle.ArcGISLightGray);
_myMapView.Map.InitialViewpoint = new Viewpoint(51.5017, -0.12714, 20000);
// Create and add two overlapping polygon graphics to operate on.
CreatePolygonsOverlay();
}
private void _operationChoiceButton_ValueChanged(object sender, EventArgs e)
{
// 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.
switch (((UISegmentedControl) sender).SelectedSegment)
{
case 0:
resultPolygon = GeometryEngine.Difference(polygonOne, polygonTwo);
break;
case 1:
resultPolygon = GeometryEngine.Intersection(polygonOne, polygonTwo);
break;
case 2:
resultPolygon = GeometryEngine.SymmetricDifference(polygonOne, polygonTwo);
break;
case 3:
resultPolygon = GeometryEngine.Union(polygonOne, polygonTwo);
break;
}
// Create a black outline symbol to use for the result polygon.
SimpleLineSymbol outlineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, Color.Black, 1);
// Create a solid red fill symbol for the result polygon graphic.
SimpleFillSymbol resultSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle.Solid, 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 CreatePolygonsOverlay()
{
// Create a black outline symbol to use for the polygons.
SimpleLineSymbol outlineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, 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, 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, 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);
}
public override void ViewDidLoad()
{
base.ViewDidLoad();
Initialize();
}
public override void LoadView()
{
// Create the views.
View = new UIView() { BackgroundColor = ApplicationTheme.BackgroundColor };
_myMapView = new MapView();
_myMapView.TranslatesAutoresizingMaskIntoConstraints = false;
_operationChoiceButton = new UISegmentedControl("Difference", "Intersection", "Symm. diff.", "Union")
{
BackgroundColor = ApplicationTheme.BackgroundColor,
TranslatesAutoresizingMaskIntoConstraints = false
};
// Clean up borders of segmented control - avoid corner pixels.
_operationChoiceButton.ClipsToBounds = true;
_operationChoiceButton.Layer.CornerRadius = 5;
// Add the views.
View.AddSubviews(_myMapView, _operationChoiceButton);
// Lay out views.
NSLayoutConstraint.ActivateConstraints(new[]
{
_myMapView.TopAnchor.ConstraintEqualTo(View.TopAnchor),
_myMapView.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
_myMapView.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
_myMapView.BottomAnchor.ConstraintEqualTo(View.BottomAnchor),
_operationChoiceButton.LeadingAnchor.ConstraintEqualTo(View.LayoutMarginsGuide.LeadingAnchor),
_operationChoiceButton.TrailingAnchor.ConstraintEqualTo(View.LayoutMarginsGuide.TrailingAnchor),
_operationChoiceButton.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor, 8)
});
}
public override void ViewWillAppear(bool animated)
{
base.ViewWillAppear(animated);
// Subscribe to events.
_operationChoiceButton.ValueChanged += _operationChoiceButton_ValueChanged;
}
public override void ViewDidDisappear(bool animated)
{
base.ViewDidDisappear(animated);
// Unsubscribe from events, per best practice.
_operationChoiceButton.ValueChanged -= _operationChoiceButton_ValueChanged;
}
}
}