Analyze viewshed (geoprocessing)

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Calculate a viewshed using a geoprocessing service, in this case showing what parts of a landscape are visible from points on mountainous terrain.

Image of viewshed geoprocessing

Use case

A viewshed is used to highlight what is visible from a given point. A viewshed could be created to show what a hiker might be able to see from a given point at the top of a mountain. Equally, a viewshed could also be created from a point representing the maximum height of a proposed wind turbine to see from what areas the turbine would be visible.

How to use the sample

Tap the map to see all areas visible from that point within a 15km radius. Clicking on an elevated area will highlight a larger part of the surrounding landscape. It may take a few seconds for the task to run and send back the results.

How it works

  1. Create a GeoprocessingTask object with the URL set to a geoprocessing service endpoint.
  2. Create a FeatureCollectionTable object and add a new Feature object whose geometry is the viewshed's observer Point.
  3. Make a GeoprocessingParameters object passing in the observer point.
  4. Use the geoprocessing task to create a GeoprocessingJob object with the parameters.
  5. Start the job and wait for it to complete and return a GeoprocessingResult object.
  6. Get the resulting GeoprocessingFeatures object.
  7. Iterate through the viewshed features to use their geometry or display the geometry in a new Graphic object.

Relevant API

  • FeatureCollectionTable
  • GeoprocessingFeatures
  • GeoprocessingJob
  • GeoprocessingParameters
  • GeoprocessingResult
  • GeoprocessingTask

Tags

geoprocessing, heat map, heatmap, viewshed

Sample Code

AnalyzeViewshed.cs
                                                                                                                                                                                                                                                                     
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// Copyright 2017 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 System;
using System.Collections.Generic;
using System.Threading.Tasks;
using Esri.ArcGISRuntime.Data;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.Tasks;
using Esri.ArcGISRuntime.Tasks.Geoprocessing;
using Esri.ArcGISRuntime.UI;
using Esri.ArcGISRuntime.UI.Controls;
using Foundation;
using UIKit;

namespace ArcGISRuntime.Samples.AnalyzeViewshed
{
    [Register("AnalyzeViewshed")]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Analyze viewshed (geoprocessing)",
        category: "Geoprocessing",
        description: "Calculate a viewshed using a geoprocessing service, in this case showing what parts of a landscape are visible from points on mountainous terrain.",
        instructions: "Tap the map to see all areas visible from that point within a 15km radius. Clicking on an elevated area will highlight a larger part of the surrounding landscape. It may take a few seconds for the task to run and send back the results.",
        tags: new[] { "geoprocessing", "heat map", "heatmap", "viewshed" })]
    public class AnalyzeViewshed : UIViewController
    {
        // Hold references to UI controls.
        private MapView _myMapView;
        private UIActivityIndicatorView _activityIndicator;

        // URL for the geoprocessing service.
        private const string ViewshedServiceUrl = "https://sampleserver6.arcgisonline.com/arcgis/rest/services/Elevation/ESRI_Elevation_World/GPServer/Viewshed";

        // The graphics overlay to show where the user clicked in the map.
        private GraphicsOverlay _inputOverlay;

        // The graphics overlay to display the result of the viewshed analysis.
        private GraphicsOverlay _resultOverlay;

        public AnalyzeViewshed()
        {
            Title = "Viewshed (Geoprocessing)";
        }

        private void Initialize()
        {
            // Create and show a map with topographic basemap and an initial location.
            _myMapView.Map = new Map(BasemapType.Topographic, 45.3790902612337, 6.84905317262762, 13);

            // Create empty overlays for the user clicked location and the results of the viewshed analysis.
            CreateOverlays();
        }

        private async void MyMapView_GeoViewTapped(object sender, GeoViewInputEventArgs e)
        {
            // Show the loading indicator.
            _activityIndicator.StartAnimating();

            // Clear previous user click location and the viewshed geoprocessing task results.
            _inputOverlay.Graphics.Clear();
            _resultOverlay.Graphics.Clear();

            // Get the tapped point.
            MapPoint geometry = e.Location;

            // Create a marker graphic where the user clicked on the map and add it to the existing graphics overlay.
            Graphic inputGraphic = new Graphic(geometry);
            _inputOverlay.Graphics.Add(inputGraphic);

            // Normalize the geometry if wrap-around is enabled.
            //    This is necessary because of how wrapped-around map coordinates are handled by Runtime.
            //    Without this step, the task may fail because wrapped-around coordinates are out of bounds.
            if (_myMapView.IsWrapAroundEnabled)
            {
                geometry = (MapPoint) GeometryEngine.NormalizeCentralMeridian(geometry);
            }

            try
            {
                // Execute the geoprocessing task using the user click location.
                await CalculateViewshed(geometry);
            }
            catch (Exception ex)
            {
                new UIAlertView("Error", ex.ToString(), (IUIAlertViewDelegate) null, "OK", null).Show();
            }
            finally
            {
                _activityIndicator.StopAnimating();
            }
        }

        private async Task CalculateViewshed(MapPoint location)
        {
            // This function will define a new geoprocessing task that performs a custom viewshed analysis based upon a
            // user click on the map and then display the results back as a polygon fill graphics overlay. If there
            // is a problem with the execution of the geoprocessing task an error message will be displayed.

            // Create new geoprocessing task using the URL defined in the member variables section.
            GeoprocessingTask viewshedTask = await GeoprocessingTask.CreateAsync(new Uri(ViewshedServiceUrl));

            // Create a new feature collection table based upon point geometries using the current map view spatial reference.
            FeatureCollectionTable inputFeatures = new FeatureCollectionTable(new List<Field>(), GeometryType.Point, _myMapView.SpatialReference);

            // Create a new feature from the feature collection table. It will not have a coordinate location (x,y) yet.
            Feature inputFeature = inputFeatures.CreateFeature();

            // Assign a physical location to the new point feature based upon where the user clicked in the map view.
            inputFeature.Geometry = location;

            // Add the new feature with (x,y) location to the feature collection table.
            await inputFeatures.AddFeatureAsync(inputFeature);

            // Create the parameters that are passed to the used geoprocessing task.
            GeoprocessingParameters viewshedParameters = new GeoprocessingParameters(GeoprocessingExecutionType.SynchronousExecute)
            {
                OutputSpatialReference = _myMapView.SpatialReference
            };

            // Add an input location to the geoprocessing parameters.
            viewshedParameters.Inputs.Add("Input_Observation_Point", new GeoprocessingFeatures(inputFeatures));

            // Create the job that handles the communication between the application and the geoprocessing task.
            GeoprocessingJob viewshedJob = viewshedTask.CreateJob(viewshedParameters);

            try
            {
                // Execute analysis and wait for the results.
                GeoprocessingResult analysisResult = await viewshedJob.GetResultAsync();

                // Get the results from the outputs.
                GeoprocessingFeatures viewshedResultFeatures = (GeoprocessingFeatures) analysisResult.Outputs["Viewshed_Result"];

                // Add all the results as a graphics to the map.
                foreach (Feature feature in viewshedResultFeatures.Features)
                {
                    _resultOverlay.Graphics.Add(new Graphic(feature.Geometry));
                }
            }
            catch (Exception ex)
            {
                // Display an error message if there is a problem.
                if (viewshedJob.Status == JobStatus.Failed && viewshedJob.Error != null)
                {
                    // Report error
                    UIAlertController alert = UIAlertController.Create("Geoprocessing Error", viewshedJob.Error.Message, UIAlertControllerStyle.Alert);
                    alert.AddAction(UIAlertAction.Create("OK", UIAlertActionStyle.Default, null));
                    PresentViewController(alert, true, null);
                }
                else
                {
                    // Report error
                    UIAlertController alert = UIAlertController.Create("Sample Error", ex.ToString(), UIAlertControllerStyle.Alert);
                    alert.AddAction(UIAlertAction.Create("OK", UIAlertActionStyle.Default, null));
                    PresentViewController(alert, true, null);
                }
            }
        }

        private void CreateOverlays()
        {
            // This function will create the overlays that show the user clicked location and the results of the
            // viewshed analysis. Note: the overlays will not be populated with any graphics at this point

            // Create renderer for input graphic. Set the size and color properties for the simple renderer.
            SimpleRenderer inputRenderer = new SimpleRenderer
            {
                Symbol = new SimpleMarkerSymbol
                {
                    Size = 15,
                    Color = System.Drawing.Color.Red
                }
            };

            // Create overlay to show input graphic.
            _inputOverlay = new GraphicsOverlay
            {
                Renderer = inputRenderer
            };

            // Create fill renderer for output of the viewshed analysis. Set the color property of the simple renderer.
            SimpleRenderer resultRenderer = new SimpleRenderer
            {
                Symbol = new SimpleFillSymbol
                {
                    Color = System.Drawing.Color.FromArgb(100, 226, 119, 40)
                }
            };

            // Create overlay to show the result.
            _resultOverlay = new GraphicsOverlay
            {
                Renderer = resultRenderer
            };

            // Add the created overlays to the MapView.
            _myMapView.GraphicsOverlays.Add(_inputOverlay);
            _myMapView.GraphicsOverlays.Add(_resultOverlay);
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();
            Initialize();
        }

        public override void LoadView()
        {
            // Create the views.
            View = new UIView() { BackgroundColor = ApplicationTheme.BackgroundColor };

            _myMapView = new MapView();
            _myMapView.TranslatesAutoresizingMaskIntoConstraints = false;

            _activityIndicator = new UIActivityIndicatorView(UIActivityIndicatorViewStyle.WhiteLarge);
            _activityIndicator.TranslatesAutoresizingMaskIntoConstraints = false;
            _activityIndicator.HidesWhenStopped = true;
            _activityIndicator.BackgroundColor = UIColor.FromWhiteAlpha(0, .5f);

            // Add the views.
            View.AddSubviews(_myMapView, _activityIndicator);

            // Lay out the views.
            NSLayoutConstraint.ActivateConstraints(new[]
            {
                _myMapView.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                _myMapView.BottomAnchor.ConstraintEqualTo(View.BottomAnchor),
                _myMapView.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _myMapView.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                _activityIndicator.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                _activityIndicator.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _activityIndicator.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                _activityIndicator.BottomAnchor.ConstraintEqualTo(View.BottomAnchor)
            });
        }

        public override void ViewWillAppear(bool animated)
        {
            base.ViewWillAppear(animated);

            // Subscribe to events.
            _myMapView.GeoViewTapped += MyMapView_GeoViewTapped;
        }

        public override void ViewDidDisappear(bool animated)
        {
            base.ViewDidDisappear(animated);

            // Unsubscribe from events, per best practice.
            _myMapView.GeoViewTapped -= MyMapView_GeoViewTapped;
        }
    }
}

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