Spatial operations

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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.

How it works

  1. Create a GraphicsOverlay and add it to the MapView.
  2. Use PolygonBuilder to create two polygons.
  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

SpatialOperations.qmlSpatialOperations.cppSpatialOperations.h
                                                          
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// [WriteFile Name=SpatialOperations, Category=Geometry]
// [Legal]
// 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.
// [Legal]

import QtQuick 2.6
import QtQuick.Layouts 1.3
import QtQuick.Controls 2.2
import Esri.Samples 1.0

SpatialOperationsSample {
    id: rootRectangle
    clip: true
    width: 800
    height: 600

    // add a mapView component
    MapView {
        id: mapQuickView
        anchors.fill: parent
    }
    mapView: mapQuickView

    // Display a ComboBox with options for each operation
    ComboBox {
        id: comboBox
        anchors {
            left: parent.left
            top: parent.top
            margins: 10
        }
        property int modelWidth: 0
        width: modelWidth + leftPadding + rightPadding + indicator.width
        model: geometryOperations
        onCurrentIndexChanged: applyGeometryOperation(currentIndex);
        Component.onCompleted : {
            for (let i = 0; i < model.length; ++i) {
                metrics.text = model[i];
                modelWidth = Math.max(modelWidth, metrics.width);
            }
        }
        TextMetrics {
            id: metrics
            font: comboBox.font
        }
    }
}

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