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.cppSpatialOperations.cppSpatialOperations.hSpatialOperations.qml
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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]

#ifdef PCH_BUILD
#include "pch.hpp"
#endif // PCH_BUILD

#include "SpatialOperations.h"

#include "Map.h"
#include "MapQuickView.h"
#include "Basemap.h"
#include "Point.h"
#include "Part.h"
#include "PolygonBuilder.h"
#include "SimpleFillSymbol.h"
#include "SimpleLineSymbol.h"
#include "GeometryEngine.h"

using namespace Esri::ArcGISRuntime;

SpatialOperations::SpatialOperations(QQuickItem* parent /* = nullptr */):
  QQuickItem(parent),
  m_polygon1(Geometry()),
  m_polygon2(Geometry()),
  m_inputsOverlay (new GraphicsOverlay(this)),
  m_outputsOverlay (new GraphicsOverlay(this)),
  m_geometryOperations { QStringLiteral("None"),       QStringLiteral("Union")
                       , QStringLiteral("Difference"), QStringLiteral("Symmetric difference")
                       , QStringLiteral("Intersection") }
{

}

void SpatialOperations::init()
{
  // Register the map view for QML
  qmlRegisterType<MapQuickView>("Esri.Samples", 1, 0, "MapView");
  qmlRegisterType<SpatialOperations>("Esri.Samples", 1, 0, "SpatialOperationsSample");
}

void SpatialOperations::componentComplete()
{
  QQuickItem::componentComplete();

  m_map = new Map(BasemapStyle::ArcGISTopographic, this);
  m_mapView->setMap(m_map);

  addPolygons();
  m_mapView->graphicsOverlays()->append(m_inputsOverlay);
  m_mapView->graphicsOverlays()->append(m_outputsOverlay);
  m_map->setInitialViewpoint(Viewpoint(Point(-13453, 6710127, SpatialReference::webMercator()), 30000));
}
void SpatialOperations::addPolygons()
{
  // create blue polygon
  PolygonBuilder polygonBuilder1(SpatialReference::webMercator());
  polygonBuilder1.addPoint(-13960, 6709400);
  polygonBuilder1.addPoint(-14660, 6710000);
  polygonBuilder1.addPoint(-13760, 6710730);
  polygonBuilder1.addPoint(-13300, 6710500);
  polygonBuilder1.addPoint(-13160, 6710100);

  SimpleFillSymbol* fillSymbol1 = new SimpleFillSymbol(SimpleFillSymbolStyle::Solid, QColor("blue"), this);
  m_polygon1 = polygonBuilder1.toGeometry();
  m_inputsOverlay->graphics()->append(new Graphic(m_polygon1, fillSymbol1, this));

  // create green polygon
  // outer ring
  Part* outerRing = new Part(SpatialReference::webMercator(), this);
  outerRing->addPoint(-13060, 6711030);
  outerRing->addPoint(-12160, 6710730);
  outerRing->addPoint(-13160, 6709700);
  outerRing->addPoint(-14560, 6710730);
  outerRing->addPoint(-13060, 6711030);

  // inner ring
  Part* innerRing = new Part(SpatialReference::webMercator(), this);
  innerRing->addPoint(-13060, 6710910);
  innerRing->addPoint(-14160, 6710630);
  innerRing->addPoint(-13160, 6709900);
  innerRing->addPoint(-12450, 6710660);
  innerRing->addPoint(-13060, 6710910);

  PolygonBuilder polygonBuilder2(SpatialReference::webMercator());
  polygonBuilder2.parts()->addPart(outerRing);
  polygonBuilder2.parts()->addPart(innerRing);
  m_polygon2 = polygonBuilder2.toGeometry();
  SimpleFillSymbol* fillSymbol2 = new SimpleFillSymbol(SimpleFillSymbolStyle::Solid, QColor("green"), this);
  m_inputsOverlay->graphics()->append(new Graphic(m_polygon2, fillSymbol2, this));
}

MapQuickView* SpatialOperations::mapQuickView() const
{
  return m_mapView;
}

void SpatialOperations::setMapQuickView(MapQuickView* mapQuickView)
{
  m_mapView = mapQuickView;
  emit mapQuickViewChanged();
}

void SpatialOperations::applyGeometryOperation(int index)
{
  if (!m_map || m_map->loadStatus() != LoadStatus::Loaded)
    return;

  // Perform geometry calculations
  Geometry resultPolygon;
  switch (index) {
  case 1:
    resultPolygon = GeometryEngine::unionOf(m_polygon1, m_polygon2);
    break;
  case 2:
    resultPolygon = GeometryEngine::difference(m_polygon1, m_polygon2);
    break;
  case 3:
    resultPolygon = GeometryEngine::symmetricDifference(m_polygon1, m_polygon2);
    break;
  case 4:
    resultPolygon = GeometryEngine::intersection(m_polygon1, m_polygon2);
    break;
  case 0:
  default:
    break;
  }

  // Clear previous results
  m_outputsOverlay->graphics()->clear();
  if (resultPolygon.isEmpty())
    return;

  // Add the resulting polygon as a Graphic
  SimpleFillSymbol* fillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle::Solid, QColor("red"), this);
  Graphic* graphic = new Graphic(resultPolygon, fillSymbol, this);
  m_outputsOverlay->graphics()->append(graphic);
}

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