Convex hull | ArcGIS Maps SDK for Qt

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Sample viewer app

Create a convex hull for a given set of points. The convex hull is a polygon with shortest perimeter that encloses a set of points. As a visual analogy, consider a set of points as nails in a board. The convex hull of the points would be like a rubber band stretched around the outermost nails.

Use case

A convex hull can be useful in collision detection. For example, when charting the position of two yacht fleets (with each vessel represented by a point), if their convex hulls have been precomputed, it is efficient to first check if their convex hulls intersect before computing their proximity point-by-point.

How to use the sample

Tap on the map to add points. Click “Convex hull” button to generate the convex hull of those points. Click the “Reset” button to start over.

How it works

Create an input geometry such as a Multipoint object.
Use GeometryEngine::convexHull(inputGeometry)to create a new Geometry object representing the convex hull of the input points. The returned geometry will either be a Point, Polyline, or Polygon based on the number of input points.

Relevant API

Geometry
GeometryEngine

Sample Code

ConvexHull.cpp

ConvexHull.h

ConvexHull.qml

main.cpp

main.qml

// [WriteFile Name=ConvexHull, Category=Geometry]
// [Legal]
// Copyright 2020 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

// sample headers
#include "ConvexHull.h"

// ArcGIS Maps SDK headers
#include "Error.h"
#include "Geometry.h"
#include "GeometryEngine.h"
#include "GeometryTypes.h"
#include "Graphic.h"
#include "GraphicListModel.h"
#include "GraphicsOverlay.h"
#include "GraphicsOverlayListModel.h"
#include "Map.h"
#include "MapQuickView.h"
#include "MapTypes.h"
#include "MultipointBuilder.h"
#include "Point.h"
#include "PointCollection.h"
#include "SimpleFillSymbol.h"
#include "SimpleLineSymbol.h"
#include "SimpleMarkerSymbol.h"
#include "SpatialReference.h"
#include "SymbolTypes.h"

using namespace Esri::ArcGISRuntime;

ConvexHull::ConvexHull(QObject* parent /* = nullptr */):
  QObject(parent),
  m_map(new Map(BasemapStyle::ArcGISTopographic, this))
{
  setupGraphics();
}

ConvexHull::~ConvexHull() = default;

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

MapQuickView* ConvexHull::mapView() const
{
  return m_mapView;
}

void ConvexHull::displayConvexHull()
{
  if (m_inputsGraphic->geometry().isEmpty())
    return;

  // normalizing the geometry before performing geometric operations
  const Geometry normalizedPoints = GeometryEngine::normalizeCentralMeridian(m_inputsGraphic->geometry());
  const Geometry convexHull = GeometryEngine::convexHull(normalizedPoints);

  // change the symbol based on the returned geometry type
  if (convexHull.geometryType() == GeometryType::Point)
  {
    m_convexHullGraphic->setSymbol(m_markerSymbol);
  }
  else if (convexHull.geometryType() == GeometryType::Polyline)
  {
    m_convexHullGraphic->setSymbol(m_lineSymbol);
  }
  else if (convexHull.geometryType() == GeometryType::Polygon)
  {
    m_convexHullGraphic->setSymbol(m_fillSymbol);
  }
  else
  {
    qWarning("Not a valid geometry.");
  }

  m_convexHullGraphic->setGeometry(convexHull);
}

void ConvexHull::clearGraphics()
{
  if (m_multipointBuilder)
    m_multipointBuilder->points()->removeAll();
  if (m_inputsGraphic)
    m_inputsGraphic->setGeometry(Geometry());
  if (m_convexHullGraphic)
    m_convexHullGraphic->setGeometry(Geometry());
}

void ConvexHull::setupGraphics()
{
  // graphics overlay to show clicked points and convex hull
  m_graphicsOverlay = new GraphicsOverlay(this);

  // create a graphic to show clicked points
  m_markerSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Circle, Qt::red, 10, this);
  m_inputsGraphic = new Graphic(this);
  m_inputsGraphic->setSymbol(m_markerSymbol);
  m_graphicsOverlay->graphics()->append(m_inputsGraphic);

  // create a graphic to display the convex hull
  m_convexHullGraphic = new Graphic(this);
  m_graphicsOverlay->graphics()->append(m_convexHullGraphic);

  // create a graphic to show the convex hull
  m_lineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle::Solid, Qt::blue, 3, this);
  m_fillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle::Null, Qt::transparent, m_lineSymbol, this);
}

void ConvexHull::getInputs()
{
  // show clicked points on MapView
  connect(m_mapView, &MapQuickView::mouseClicked, this, [this](QMouseEvent& e)
  {
    e.accept();

    const Point clickedPoint = m_mapView->screenToLocation(e.position().x(), e.position().y());
    m_multipointBuilder->points()->addPoint(clickedPoint);
    m_inputsGraphic->setGeometry(m_multipointBuilder->toGeometry());
  });
}

// Set the view (created in QML)
void ConvexHull::setMapView(MapQuickView* mapView)
{
  if (!mapView || mapView == m_mapView)
    return;

  m_mapView = mapView;
  m_mapView->setMap(m_map);

  // wait for map to load before creating multipoint builder
  connect(m_map, &Map::doneLoading, this, [this](const Error& e){
    if (!e.isEmpty())
    {
      qDebug() << e.message() << e.additionalMessage();
      return;
    }

    if (m_map->loadStatus() == LoadStatus::FailedToLoad)
    {
      qWarning( "Failed to load map.");
      return;
    }

    m_multipointBuilder = new MultipointBuilder(m_map->spatialReference(), this);
  });

  getInputs();

  m_mapView->graphicsOverlays()->append(m_graphicsOverlay);
  emit mapViewChanged();
}

// [WriteFile Name=ConvexHull, Category=Geometry]
// [Legal]
// Copyright 2020 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]

#ifndef CONVEXHULL_H
#define CONVEXHULL_H

// Qt headers
#include <QList>
#include <QObject>

namespace Esri::ArcGISRuntime
{
class Graphic;
class GraphicsOverlay;
class Map;
class MapQuickView;
class MultipointBuilder;
class SimpleFillSymbol;
class SimpleLineSymbol;
class SimpleMarkerSymbol;
}

Q_MOC_INCLUDE("MapQuickView.h")

class ConvexHull : public QObject
{
  Q_OBJECT

  Q_PROPERTY(Esri::ArcGISRuntime::MapQuickView* mapView READ mapView WRITE setMapView NOTIFY mapViewChanged)

public:
  explicit ConvexHull(QObject* parent = nullptr);
  ~ConvexHull();

  static void init();

  Q_INVOKABLE void displayConvexHull();
  Q_INVOKABLE void clearGraphics();

signals:
  void mapViewChanged();

private:
  Esri::ArcGISRuntime::MapQuickView* mapView() const;
  void setMapView(Esri::ArcGISRuntime::MapQuickView* mapView);

  void setupGraphics();
  void getInputs();

  Esri::ArcGISRuntime::Map* m_map = nullptr;
  Esri::ArcGISRuntime::MapQuickView* m_mapView = nullptr;

  Esri::ArcGISRuntime::Graphic* m_inputsGraphic = nullptr;
  Esri::ArcGISRuntime::Graphic* m_convexHullGraphic = nullptr;
  Esri::ArcGISRuntime::GraphicsOverlay* m_graphicsOverlay = nullptr;
  Esri::ArcGISRuntime::SimpleFillSymbol* m_fillSymbol = nullptr;
  Esri::ArcGISRuntime::SimpleLineSymbol* m_lineSymbol = nullptr;
  Esri::ArcGISRuntime::SimpleMarkerSymbol* m_markerSymbol = nullptr;
  Esri::ArcGISRuntime::MultipointBuilder* m_multipointBuilder = nullptr;
};

#endif // CONVEXHULL_H

// [WriteFile Name=ConvexHull, Category=Geometry]
// [Legal]
// Copyright 2020 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
import QtQuick.Controls
import Esri.Samples
import QtQuick.Layouts

Item {

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

        Component.onCompleted: {
            // Set the focus on MapView to initially enable keyboard navigation
            forceActiveFocus();
        }

        RowLayout {
            anchors {
                left: parent.left
                top: parent.top
            }

            Button {
                Layout.fillWidth: true
                Layout.fillHeight: true
                text: "Convex hull"
                onClicked: {
                    model.displayConvexHull();
                }
            }

            Button {
                Layout.fillWidth: true
                Layout.fillHeight: true
                text: "Reset"
                onClicked: {
                    model.clearGraphics();
                }
            }
        }
    }

    // Declare the C++ instance which creates the map etc. and supply the view
    ConvexHullSample {
        id: model
        mapView: view
    }
}

// [Legal]
// Copyright 2020 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]

// sample headers
#include "ConvexHull.h"

// ArcGIS Maps SDK headers
#include "ArcGISRuntimeEnvironment.h"

// Qt headers
#include <QDir>
#include <QGuiApplication>
#include <QQmlApplicationEngine>

// Platform specific headers
#ifdef Q_OS_WIN
#include <Windows.h>
#endif

int main(int argc, char *argv[])
{
  Esri::ArcGISRuntime::ArcGISRuntimeEnvironment::setUseLegacyAuthentication(false);
  QGuiApplication app(argc, argv);
  app.setApplicationName(QString("ConvexHull"));

  // Use of ArcGIS location services, such as basemap styles, geocoding, and routing services,
  // requires an access token. For more information see
  // https://links.esri.com/arcgis-runtime-security-auth.

  // The following methods grant an access token:

  // 1. User authentication: Grants a temporary access token associated with a user's ArcGIS account.
  // To generate a token, a user logs in to the app with an ArcGIS account that is part of an
  // organization in ArcGIS Online or ArcGIS Enterprise.

  // 2. API key authentication: Get a long-lived access token that gives your application access to
  // ArcGIS location services. Go to the tutorial at https://links.esri.com/create-an-api-key.
  // Copy the API Key access token.

  const QString accessToken = QString("");

  if (accessToken.isEmpty())
  {
      qWarning() << "Use of ArcGIS location services, such as the basemap styles service, requires" <<
                    "you to authenticate with an ArcGIS account or set the API Key property.";
  }
  else
  {
      Esri::ArcGISRuntime::ArcGISRuntimeEnvironment::setApiKey(accessToken);
  }

  // Initialize the sample
  ConvexHull::init();

  // Initialize application view
  QQmlApplicationEngine engine;
  // Add the import Path
  engine.addImportPath(QDir(QCoreApplication::applicationDirPath()).filePath("qml"));

#ifdef ARCGIS_RUNTIME_IMPORT_PATH_2
  engine.addImportPath(ARCGIS_RUNTIME_IMPORT_PATH_2);
#endif

  // Set the source
  engine.load(QUrl("qrc:/Samples/Geometry/ConvexHull/main.qml"));

  return app.exec();
}

// Copyright 2020 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.

import QtQuick.Controls
import Esri.Samples

ApplicationWindow {
    visible: true
    width: 800
    height: 600

    ConvexHull {
        anchors.fill: parent
    }
}

Use case

How to use the sample

How it works

Relevant API

Tags

Sample Code