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Nearest vertex | ArcGIS Maps SDK for Qt

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Find the closest vertex and coordinate of a geometry to a point.

Determine the shortest distance between a location and the boundary of an area. For example, developers can snap imprecise user clicks to a geometry if the click is within a certain distance of the geometry.

Click anywhere on the map. A yellow cross will show at that location. A blue circle will show the polygon's nearest vertex to the point that was clicked. A red diamond will appear at the coordinate on the geometry that is nearest to the point that was clicked. If clicked inside the geometry, the red and orange markers will overlap. The information box showing distance between the clicked point and the nearest vertex/coordinate will be updated with every new location clicked.

1. Get a Geometry and a Point to check the nearest vertex against.
2. Call GeometryEngine::nearestVertex(inputGeometry, point).
3. Use the returned ProximityResult to get the Point representing the polygon vertex, and to determine the distance between that vertex and the clicked point.
4. Call GeometryEngine::nearestCoordinate(inputGeometry, point).
5. Use the returned ProximityResult to get the Point representing the coordinate on the polygon, and to determine the distance between that coordinate and the clicked point.

• GeometryEngine
• ProximityResult

The value of ProximityResult::distance() is planar (Euclidean) distance. Planar distances are only accurate for geometries that have a defined projected coordinate system, which maintain the desired level of accuracy. The example polygon in this sample is defined in California State Plane Coordinate System - Zone 5 (WKID 2229), which maintains accuracy near Southern California. Accuracy declines outside the state plane zone.

analysis, coordinate, geometry, nearest, proximity, vertex

NearestVertex.cpp NearestVertex.cpp NearestVertex.h NearestVertex.qml

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// [WriteFile Name=NearestVertex, 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 "NearestVertex.h"

// ArcGIS Maps SDK headers
#include "Basemap.h"
#include "Envelope.h"
#include "FeatureLayer.h"
#include "GeometryEngine.h"
#include "Graphic.h"
#include "GraphicListModel.h"
#include "GraphicsOverlay.h"
#include "GraphicsOverlayListModel.h"
#include "LayerListModel.h"
#include "Map.h"
#include "MapQuickView.h"
#include "Point.h"
#include "PolygonBuilder.h"
#include "PortalItem.h"
#include "ProximityResult.h"
#include "SimpleFillSymbol.h"
#include "SimpleLineSymbol.h"
#include "SimpleMarkerSymbol.h"
#include "SpatialReference.h"
#include "SymbolTypes.h"

// Qt headers
#include <QFuture>

using namespace Esri::ArcGISRuntime;

namespace {
  const SpatialReference statePlaneCaliforniaZone5SpatialReference = SpatialReference(2229);
}

NearestVertex::NearestVertex(QObject* parent /* = nullptr */):
  QObject(parent)
{
  m_map = new Map(statePlaneCaliforniaZone5SpatialReference, this);

  PortalItem* portalItem = new PortalItem("8c2d6d7df8fa4142b0a1211c8dd66903", this);
  FeatureLayer* usStatesGeneralizedLayer = new FeatureLayer(portalItem, this);
  m_map->basemap()->baseLayers()->append(usStatesGeneralizedLayer);
}

NearestVertex::~NearestVertex() = default;

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

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

int NearestVertex::vertexDistance() const
{
  return m_vertexDistance;
}

int NearestVertex::coordinateDistance() const
{
  return m_coordinateDistance;
}

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

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

  // shows the polygon, clicked location, and nearest coordinate and vertex on polygon
  setupGraphics();

  // Set viewpoint to the polygon graphic
  m_mapView->setViewpointCenterAsync(m_mapView->graphicsOverlays()->first()->graphics()->first()->geometry().extent().center(), 8e6);

  emit mapViewChanged();
}

void NearestVertex::setupGraphics()
{
  // create a graphics overlay to show the polygon, clicked location, and nearest vertex
  GraphicsOverlay* graphicsOverlay = new GraphicsOverlay(this);

  // Construct a polygon from a point collection that uses the California zone 5 (ftUS) state plane coordinate system
  QList<Point> points = {
    Point(6627416.41469281, 1804532.53233782),
    Point(6669147.89779046, 2479145.16609522),
    Point(7265673.02678292, 2484254.50442408),
    Point(7676192.55880379, 2001458.66365744),
    Point(7175695.94143837, 1840722.34474458)
  };

  PolygonBuilder* polygonBuilder = new PolygonBuilder(statePlaneCaliforniaZone5SpatialReference, this);
  polygonBuilder->addPoints(points);
  SimpleLineSymbol* polygonOutlineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle::Solid, Qt::green, 2, this);
  SimpleFillSymbol* polygonFillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle::ForwardDiagonal, Qt::green, polygonOutlineSymbol, this);
  Graphic* polygonGraphic = new Graphic(polygonBuilder->toGeometry(), polygonFillSymbol, this);

  graphicsOverlay->graphics()->append(polygonGraphic);

  // create graphics for the clicked location, nearest coordinate, and nearest vertex markers
  SimpleMarkerSymbol* clickedLocationSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::X, Qt::yellow, 15, this);
  SimpleMarkerSymbol* nearestCoordinateSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Diamond, Qt::red, 10, this);
  SimpleMarkerSymbol* nearestVertexSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Circle, Qt::blue, 15, this);

  Graphic* clickedLocationGraphic = new Graphic(this);
  clickedLocationGraphic->setSymbol(clickedLocationSymbol);
  Graphic* nearestCoordinateGraphic = new Graphic(this);
  nearestCoordinateGraphic->setSymbol(nearestCoordinateSymbol);
  Graphic* nearestVertexGraphic = new Graphic(this);
  nearestVertexGraphic->setSymbol(nearestVertexSymbol);

  graphicsOverlay->graphics()->append(clickedLocationGraphic);
  graphicsOverlay->graphics()->append(nearestCoordinateGraphic);
  graphicsOverlay->graphics()->append(nearestVertexGraphic);

  // add graphic to clicked location
  connect(m_mapView, &MapQuickView::mouseClicked, this,
          [nearestVertexGraphic, nearestCoordinateGraphic, polygonBuilder, clickedLocationGraphic, this]
          (QMouseEvent& e)
  {
    const Point clickedLocation = m_mapView->screenToLocation(e.position().x(), e.position().y());
    // normalizing the geometry before performing geometric operations
    const Point normalizedPoint = geometry_cast<Point>(GeometryEngine::normalizeCentralMeridian(clickedLocation));

    clickedLocationGraphic->setGeometry(normalizedPoint);

    const ProximityResult nearestCoordinateResult = GeometryEngine::nearestCoordinate(polygonBuilder->toGeometry(), normalizedPoint);
    nearestCoordinateGraphic->setGeometry(nearestCoordinateResult.coordinate());

    const ProximityResult nearestVertexResult = GeometryEngine::nearestVertex(polygonBuilder->toGeometry(), normalizedPoint);
    nearestVertexGraphic->setGeometry(nearestVertexResult.coordinate());

    // get the distances to the nearest vertex and nearest coordinate, converted from feet to miles
    m_vertexDistance = nearestVertexResult.distance()/5280;
    m_coordinateDistance = nearestCoordinateResult.distance()/5280;

    e.accept();
    emit vertexDistanceCalculated();
    emit coordinateDistanceCalculated();
  });

  m_mapView->graphicsOverlays()->append(graphicsOverlay);
}

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