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Convex hull

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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.

Image of convex hull

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

Click on the map to add points. Click the "Create Convex Hull" button to generate the convex hull of those points. Click the "Clear" button to start over.

How it works

  1. Create an input geometry such as a Multipoint object.
  2. 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

Tags

convex hull, geometry, spatial analysis

Sample Code

ConvexHullSample.java
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 /*  * 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.  */  package com.esri.samples.convex_hull;  import java.util.ArrayList; import java.util.List;  import javafx.application.Application; import javafx.geometry.Insets; import javafx.geometry.Point2D; import javafx.geometry.Pos; import javafx.scene.Scene; import javafx.scene.control.Button; import javafx.scene.input.MouseButton; import javafx.scene.layout.Background; import javafx.scene.layout.BackgroundFill; import javafx.scene.layout.CornerRadii; import javafx.scene.layout.StackPane; import javafx.scene.layout.VBox; import javafx.scene.paint.Color; import javafx.scene.paint.Paint; import javafx.stage.Stage;  import com.esri.arcgisruntime.ArcGISRuntimeEnvironment; import com.esri.arcgisruntime.geometry.Geometry; import com.esri.arcgisruntime.geometry.GeometryEngine; import com.esri.arcgisruntime.geometry.Multipoint; import com.esri.arcgisruntime.geometry.Point; import com.esri.arcgisruntime.geometry.PointCollection; import com.esri.arcgisruntime.mapping.ArcGISMap; import com.esri.arcgisruntime.mapping.BasemapStyle; import com.esri.arcgisruntime.mapping.view.Graphic; import com.esri.arcgisruntime.mapping.view.GraphicsOverlay; import com.esri.arcgisruntime.mapping.view.MapView; import com.esri.arcgisruntime.symbology.SimpleLineSymbol; import com.esri.arcgisruntime.symbology.SimpleMarkerSymbol;  public class ConvexHullSample extends Application {   private MapView mapView;   @Override  public void start(Stage stage) {   try {  // create stack pane and application scene  StackPane stackPane = new StackPane();  Scene scene = new Scene(stackPane);   // set title, size, and add scene to stage  stage.setTitle("Convex Hull Sample");  stage.setWidth(800);  stage.setHeight(700);  stage.setScene(scene);  stage.show();   // authentication with an API key or named user is required to access basemaps and other location services  String yourAPIKey = System.getProperty("apiKey");  ArcGISRuntimeEnvironment.setApiKey(yourAPIKey);   // create a map with the topographic basemap style  ArcGISMap map = new ArcGISMap(BasemapStyle.ARCGIS_TOPOGRAPHIC);   // create a map view and set the map to it  mapView = new MapView();  mapView.setMap(map);   // create a graphics overlay to show the input points and convex hull  var graphicsOverlay = new GraphicsOverlay();  mapView.getGraphicsOverlays().add(graphicsOverlay);   // create a graphic to show the points  var simpleMarkerSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbol.Style.CIRCLE, Color.RED, 10);  Graphic inputsGraphic = new Graphic();  inputsGraphic.setSymbol(simpleMarkerSymbol);  graphicsOverlay.getGraphics().add(inputsGraphic);   // create a graphic to show the convex hull as a blue outline  var simpleLineSymbol = new SimpleLineSymbol(SimpleLineSymbol.Style.SOLID, Color.BLUE, 3);  Graphic convexHullGraphic = new Graphic();  graphicsOverlay.getGraphics().add(convexHullGraphic);   // keep track of the points added by the user  List<Point> inputs = new ArrayList<>();   // create a button to create and show the convex hull  var convexHullButton = new Button("Create Convex Hull");  convexHullButton.setMaxWidth(130);  convexHullButton.setDisable(true);  convexHullButton.setOnAction(e -> {  convexHullButton.setDisable(true);  // change the symbol depending on the returned geometry type  Geometry convexHull = GeometryEngine.convexHull(inputsGraphic.getGeometry());  switch (convexHull.getGeometryType()) {  case POINT:  convexHullGraphic.setSymbol(simpleMarkerSymbol);  break;  case POLYLINE:  case POLYGON:  convexHullGraphic.setSymbol(simpleLineSymbol);  break;  }  convexHullGraphic.setGeometry(convexHull);  });   // create a button to clear all graphics  var clearButton = new Button("Clear");  clearButton.setMaxWidth(130);  clearButton.setDisable(true);  clearButton.setOnAction(e -> {  inputs.clear();  inputsGraphic.setGeometry(null);  convexHullGraphic.setGeometry(null);  convexHullButton.setDisable(true);  clearButton.setDisable(true);  });   var vBox = new VBox(6);  vBox.setPickOnBounds(false);  vBox.setBackground(new Background(new BackgroundFill(Paint.valueOf("rgba(0,0,0,0.3)"), CornerRadii.EMPTY, Insets.EMPTY)));  vBox.setPadding(new Insets(10.0));  vBox.setMaxSize(150, 50);  vBox.getStyleClass().add("panel-region");  vBox.getChildren().addAll(convexHullButton, clearButton);   // create a point from where the user clicked  mapView.setOnMouseClicked(e -> {  if (e.isStillSincePress() && e.getButton() == MouseButton.PRIMARY) {   Point2D point = new Point2D(e.getX(), e.getY());   // create a map point from a point  Point mapPoint = mapView.screenToLocation(point);   // the map point should be normalized to the central meridian when wrapping around a map, so its value stays within the coordinate system of the map view  Point normalizedMapPoint = (Point) GeometryEngine.normalizeCentralMeridian(mapPoint);   // add a point where the user clicks on the map  inputs.add(normalizedMapPoint);  // update the inputs graphic geometry  Multipoint inputsGeometry = new Multipoint(new PointCollection(inputs));  inputsGraphic.setGeometry(inputsGeometry);  // if a new point is added, enable the convex hull and clear buttons  if (inputs.size() > 0) {  convexHullButton.setDisable(false);  clearButton.setDisable(false);  }  }  });   // add the map view to the stack pane  stackPane.getChildren().addAll(mapView, vBox);  StackPane.setAlignment(vBox, Pos.TOP_LEFT);  StackPane.setMargin(vBox, new Insets(10, 0, 0, 10));  } catch (Exception e) {  // on any error, display the stack trace.  e.printStackTrace();  }  }   /**  * Stops and releases all resources used in application.  */  @Override  public void stop() {   if (mapView != null) {  mapView.dispose();  }  }   /**  * Opens and runs application.  *  * @param args arguments passed to this application  */  public static void main(String[] args) {   Application.launch(args);  }  }

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