Nearest vertex

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

screenshot

Use case

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.

How to use the sample

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 yellow 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.

How it works

  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.

Relevant API

  • GeometryEngine
  • ProximityResult

Tags

analysis, coordinate, geometry, nearest, proximity, vertex

Sample Code

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]

import QtQuick 2.6
import QtQuick.Controls 2.4
import Esri.ArcGISRuntime 100.11

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

    MapView {
        id: mapView
        anchors.fill: parent

        GraphicsOverlay {
            id: graphicsOverlay
        }

        Graphic {
            id: polygonGraphic
            SimpleFillSymbol {
                style: Enums.SimpleFillSymbolStyleForwardDiagonal
                color: "lime"
                SimpleLineSymbol {
                    style: Enums.SimpleLineSymbolStyleSolid
                    color: "lime"
                    width: 2.0
                }
            }
        }

        PolygonBuilder {
            id: polygonBuilder
            SpatialReference { wkid: 3857 }
        }

        Graphic {
            id:  clickedPointGraphic
            SimpleMarkerSymbol {
                style: Enums.SimpleMarkerSymbolStyleX
                color: "yellow"
                size: 15
            }
        }

        Graphic {
            id: nearestVertexGraphic
            SimpleMarkerSymbol {
                style: Enums.SimpleMarkerSymbolStyleCircle
                color: "blue"
                size: 15
            }
        }

        Graphic {
            id: nearestCoordinateGraphic
            SimpleMarkerSymbol {
                style: Enums.SimpleMarkerSymbolStyleDiamond
                color: "red"
                size: 10
            }
        }

        Component.onCompleted: {
            // create polygon in middle of Atlantic Ocean
            polygonBuilder.addPointXY(-5991501.677830, 5599295.131468);
            polygonBuilder.addPointXY(-6928550.398185, 2087936.739807);
            polygonBuilder.addPointXY(-3149463.800709, 1840803.011362);
            polygonBuilder.addPointXY(-1563689.043184, 3714900.452072);
            polygonBuilder.addPointXY(-3180355.516764, 5619889.608838);
            polygonGraphic.geometry = polygonBuilder.geometry;

            // append graphics to overlay
            graphicsOverlay.graphics.append(polygonGraphic);
            graphicsOverlay.graphics.append(clickedPointGraphic);
            graphicsOverlay.graphics.append(nearestVertexGraphic);
            graphicsOverlay.graphics.append(nearestCoordinateGraphic);
        }

        Map {
            Basemap {
                initStyle: Enums.BasemapStyleArcGISTopographic
            }

            ViewpointCenter {
                Point {
                    x: -4487263.495911
                    y: 3699176.480377
                    SpatialReference {wkid: 3857}
                }
                targetScale: 50000000
            }
        }
    }

    MouseArea {
        anchors.fill: parent
        onClicked: {
            const clickedPoint = mapView.screenToLocation(mouseX, mouseY);
            // normalizing the geometry before performing geometric operations
            const normalizedPoint = GeometryEngine.normalizeCentralMeridian(clickedPoint);
            clickedPointGraphic.geometry = normalizedPoint;

            const nearestVertexPoint = GeometryEngine.nearestVertex(polygonBuilder.geometry, normalizedPoint);
            nearestVertexGraphic.geometry = nearestVertexPoint.coordinate;

            const nearestCoordinateResult = GeometryEngine.nearestCoordinate(polygonBuilder.geometry, normalizedPoint);
            nearestCoordinateGraphic.geometry = nearestCoordinateResult.coordinate;

            distancesLabel.text = `Vertex distance: ${(nearestVertexPoint.distance/1000.0).toFixed()} km
Coordinate distance: ${(nearestCoordinateResult.distance/1000.0).toFixed()} km` ;
        }
    }

    // create box to display label with distances to nearest vertex and coordinate
    Rectangle
    {
        id: labelRectangle
        width: childrenRect.width
        height: childrenRect.height
        anchors {
            top: parent.top
            left: parent.left
        }
        visible: true
        color: "white"
        border.color: "black"
        border.width: 2
        Label {
            id: distancesLabel
            font.pointSize: 14
            padding: 5
            text: "Vertex Distance: 0 km\nCoordinate distance: 0 km"
        }
    }
}

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