Geodesic operations

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Calculate a geodesic path between two points and measure its distance.

Image of geodesic operations

Use case

A geodesic distance provides an accurate, real-world distance between two points. Visualizing flight paths between cities is a common example of a geodesic operation since the flight path between two airports takes into account the curvature of the earth, rather than following the planar path between those points, which appears as a straight line on a projected map.

How to use the sample

Click anywhere on the map. A line graphic will display the geodesic line between the two points. In addition, text that indicates the geodesic distance between the two points will be updated. Click elsewhere and a new line will be created.

How it works

  1. A Point is created in New York City and displayed as a Graphic.
  2. When a click occurs on the MapView, a new Point is obtained from the mouse click. This Point is added as a Graphic.
  3. A Polyline is created with the two Point objects.
  4. GeometryEngine.DensifyGeodetic is called from the Polyline object, and the returned Geometry is stored as pathGeometry.
  5. GeometryEngine.LengthGeodetic is called from pathGeometry, and the returned number is displayed on the screen.

Relevant API

  • GeometryEngine.DensifyGeodetic
  • GeometryEngine.LengthGeodetic

About the data

The Imagery basemap provides the global context for the displayed geodesic line.

Tags

densify, distance, geodesic, geodetic

Sample Code

GeodesicOperations.xaml.csGeodesicOperations.xaml.csGeodesicOperations.xaml
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// 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.

using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI;
using Esri.ArcGISRuntime.UI.Controls;

namespace ArcGIS.WPF.Samples.GeodesicOperations
{
    [ArcGIS.Samples.Shared.Attributes.Sample(
        name: "Geodesic operations",
        category: "Geometry",
        description: "Calculate a geodesic path between two points and measure its distance.",
        instructions: "Click anywhere on the map. A line graphic will display the geodesic line between the two points. In addition, text that indicates the geodesic distance between the two points will be updated. Click elsewhere and a new line will be created.",
        tags: new[] { "densify", "distance", "geodesic", "geodetic" })]
    public partial class GeodesicOperations
    {
        // Hold references to the graphics.
        private Graphic _startLocationGraphic;
        private Graphic _endLocationGraphic;
        private Graphic _pathGraphic;

        public GeodesicOperations()
        {
            InitializeComponent();

            // Create the map, set the initial extent, and add the original point graphic.
            Initialize();
        }

        private void Initialize()
        {
            MyMapView.Map = new Map(BasemapStyle.ArcGISImageryStandard);

            // Create the graphics overlay and add it to the map view.
            GraphicsOverlay graphicsOverlay = new GraphicsOverlay();
            MyMapView.GraphicsOverlays.Add(graphicsOverlay);

            // Add a graphic at JFK to serve as the origin.
            MapPoint start = new MapPoint(-73.7781, 40.6413, SpatialReferences.Wgs84);
            SimpleMarkerSymbol startMarker = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle.Circle, System.Drawing.Color.Blue, 10);
            _startLocationGraphic = new Graphic(start, startMarker);

            // Create the graphic for the destination.
            _endLocationGraphic = new Graphic
            {
                Symbol = startMarker
            };

            // Create the graphic for the path.
            _pathGraphic = new Graphic
            {
                Symbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Dash, System.Drawing.Color.Blue, 5)
            };

            // Add the graphics to the overlay.
            graphicsOverlay.Graphics.Add(_startLocationGraphic);
            graphicsOverlay.Graphics.Add(_endLocationGraphic);
            graphicsOverlay.Graphics.Add(_pathGraphic);

            // Update end location when the user taps.
            MyMapView.GeoViewTapped += MyMapViewOnGeoViewTapped;
        }

        private void MyMapViewOnGeoViewTapped(object sender, GeoViewInputEventArgs geoViewInputEventArgs)
        {
            // Get the tapped point, projected to WGS84.
            MapPoint destination = (MapPoint)geoViewInputEventArgs.Location.Project(SpatialReferences.Wgs84);

            // Update the destination graphic.
            _endLocationGraphic.Geometry = destination;

            // Get the points that define the route polyline.
            PointCollection polylinePoints = new PointCollection(SpatialReferences.Wgs84)
            {
                (MapPoint)_startLocationGraphic.Geometry,
                destination
            };

            // Create the polyline for the two points.
            Polyline routeLine = new Polyline(polylinePoints);

            // Densify the polyline to show the geodesic curve.
            Geometry pathGeometry = routeLine.DensifyGeodetic(1, LinearUnits.Kilometers, GeodeticCurveType.Geodesic);

            // Apply the curved line to the path graphic.
            _pathGraphic.Geometry = pathGeometry;

            // Calculate and show the distance.
            double distance = pathGeometry.LengthGeodetic(LinearUnits.Kilometers, GeodeticCurveType.Geodesic);
            ResultsLabel.Text = string.Format("{0} kilometers", (int)distance);
        }
    }
}

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