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
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
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
Tags
convex hull, geometry, spatial analysis
Sample Code
ConvexHullSample.java
Use dark colors for code blocksCopy
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;
publicclassConvexHullSampleextendsApplication{
private MapView mapView;
@Overridepublicvoidstart(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 hullvar graphicsOverlay = new GraphicsOverlay();
mapView.getGraphicsOverlays().add(graphicsOverlay);
// create a graphic to show the pointsvar 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 outlinevar 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 hullvar 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 graphicsvar 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 buttonsif (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.
*/@Overridepublicvoidstop(){
if (mapView != null) {
mapView.dispose();
}
}
/**
* Opens and runs application.
*
* @param args arguments passed to this application
*/publicstaticvoidmain(String[] args){
Application.launch(args);
}
}