Convex hull

Create convex hull from points


// 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:
// 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.

using Android.App;
using Android.OS;
using Android.Widget;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI;
using Esri.ArcGISRuntime.UI.Controls;
using System;
using System.Collections.Generic;

namespace ArcGISRuntime.Samples.ConvexHull
        "Convex hull",
        "This sample demonstrates how to use the GeometryEngine.ConvexHull operation to generate a polygon that encloses a series of user-tapped map points.",
        "Tap on the map in several places, then click the 'Convex Hull' button.",
        "Analysis", "ConvexHull", "GeometryEngine")]
    public class ConvexHull : Activity
        // Create and hold reference to the used MapView.
        private MapView _myMapView = new MapView();

        // Graphics overlay to display the hull.
        private GraphicsOverlay _graphicsOverlay;

        // List of geometry values (MapPoints in this case) that will be used by the GeometryEngine.ConvexHull operation.
        private List<Geometry> _inputPointsList = new List<Geometry>();

        // List of geometry values (MapPoints in this case) that will be used by the GeometryEngine.ConvexHull operation.
        private PointCollection _inputPointCollection = new PointCollection(SpatialReferences.WebMercator);

        // Create a Button to create a convex hull.
        private Button _convexHullButton;

        // Create a Button to create a convex hull.
        private Button _resetButton;

        protected override void OnCreate(Bundle bundle)
            Title = "Convex hull";

            // Create the UI, setup the control references and execute initialization.

        private void Initialize()
            // Create a map with a topographic basemap.
            Map theMap = new Map(Basemap.CreateTopographic());

            // Assign the map to the MapView.
            _myMapView.Map = theMap;

            // Create an overlay to hold the lines of the hull.
            _graphicsOverlay = new GraphicsOverlay();

            // Add the created graphics overlay to the MapView.

            // Wire up the MapView's GeoViewTapped event handler.
            _myMapView.GeoViewTapped += MyMapView_GeoViewTapped;

        private void MyMapView_GeoViewTapped(object sender, GeoViewInputEventArgs e)
                // Create a map point (in the WebMercator projected coordinate system) from the GUI screen coordinate.
                MapPoint userTappedMapPoint = _myMapView.ScreenToLocation(e.Position);

                // Add the map point to the list that will be used by the GeometryEngine.ConvexHull operation.

                // Check if there are at least three points.
                if (_inputPointCollection.Count > 2)
                    // Enable the button for creating hulls.
                    _convexHullButton.Enabled = true;

                // Create a simple marker symbol to display where the user tapped/clicked on the map. The marker symbol
                // will be a solid, red circle.
                SimpleMarkerSymbol userTappedSimpleMarkerSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle.Circle, System.Drawing.Color.Red, 10);

                // Create a new graphic for the spot where the user clicked on the map using the simple marker symbol.
                Graphic userTappedGraphic = new Graphic(userTappedMapPoint, new Dictionary<string, object>() { { "Type", "Point" } }, userTappedSimpleMarkerSymbol) { ZIndex = 0 };

                // Set the Z index for the user tapped graphic so that it appears above the convex hull graphic(s) added later.
                userTappedGraphic.ZIndex = 1;

                // Add the user tapped/clicked map point graphic to the graphic overlay.
            catch (System.Exception ex)
                // Display an error message if there is a problem adding user tapped graphics.
                AlertDialog.Builder alertBuilder = new AlertDialog.Builder(this);
                alertBuilder.SetTitle("Can't add user tapped graphic");

        private void ConvexHullButton_Click(object sender, EventArgs e)
                // Create a multi-point geometry from the user tapped input map points.
                Multipoint inputMultipoint = new Multipoint(_inputPointCollection);

                // Get the returned result from the convex hull operation.
                Geometry convexHullGeometry = GeometryEngine.ConvexHull(inputMultipoint);

                // Create a simple line symbol for the outline of the convex hull graphic(s).
                SimpleLineSymbol convexHullSimpleLineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, System.Drawing.Color.Blue, 4);

                // Create the simple fill symbol for the convex hull graphic(s) - comprised of a fill style, fill
                // color and outline. It will be a hollow (i.e.. see-through) polygon graphic with a thick red outline.
                SimpleFillSymbol convexHullSimpleFillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle.Null, System.Drawing.Color.Red,

                // Create the graphic for the convex hull - comprised of a polygon shape and fill symbol.
                Graphic convexHullGraphic = new Graphic(convexHullGeometry, new Dictionary<string, object>() { { "Type", "Hull" } }, convexHullSimpleFillSymbol) { ZIndex = 1 };

                // Remove any existing convex hull graphics from the overlay.
                foreach (Graphic g in new List<Graphic>(_graphicsOverlay.Graphics))
                    if ((string)g.Attributes["Type"] == "Hull")
                // Add the convex hull graphic to the graphics overlay.

                // Disable the button after has been used.
                _convexHullButton.Enabled = false;
            catch (System.Exception ex)
                // Display an error message if there is a problem generating convex hull operation.
                var alertBuilder = new AlertDialog.Builder(this);
                alertBuilder.SetTitle("There was a problem generating the convex hull.");

        private void ResetButton_Click(object sender, EventArgs e)
            // Clear the existing points and graphics.

            // Disable the convex hull button.
            _convexHullButton.Enabled = false;

        private void CreateLayout()
            // Create a new vertical layout for the app.
            LinearLayout layout = new LinearLayout(this) { Orientation = Orientation.Vertical };

            // Create a TextView for instructions.
            TextView sampleInstructionsTextView = new TextView(this);
            sampleInstructionsTextView.Text = "Tap on the map in several places, then click the 'Convex Hull' button.";

            // Create a Button to create the convex hull.
            _convexHullButton = new Button(this);
            _convexHullButton.Text = "Convex Hull";
            _convexHullButton.Click += ConvexHullButton_Click;
            _convexHullButton.Enabled = false;

            // Create a Button to reset the convex hull.
            _resetButton = new Button(this);
            _resetButton.Text = "Reset";
            _resetButton.Click += ResetButton_Click;

            // Add the map view to the layout.

            // Show the layout in the app.

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