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ArcGIS Runtime SDK for .NET

Analyze viewshed (geoprocessing)

This code sample is available for these platforms:
View Sample on GitHub

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

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage
    x:Class="ArcGISRuntime.Samples.AnalyzeViewshed.AnalyzeViewshed"
    xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:esriUI="clr-namespace:Esri.ArcGISRuntime.Xamarin.Forms;assembly=Esri.ArcGISRuntime.Xamarin.Forms"
    xmlns:mapping="clr-namespace:Esri.ArcGISRuntime.Mapping;assembly=Esri.ArcGISRuntime">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="auto" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <Label
            Grid.Row="0"
            Margin="10,0,0,0"
            Text="Click a location on the map to perform the viewshed analysis." />
        <esriUI:MapView x:Name="MyMapView" Grid.Row="1" />
        <ActivityIndicator
            x:Name="MyActivityIndicator"
            Grid.Row="1"
            HorizontalOptions="CenterAndExpand"
            IsVisible="False"
            VerticalOptions="CenterAndExpand" />
    </Grid>
</ContentPage>
// Copyright 2016 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.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 System;
using System.Collections.Generic;
using System.Threading.Tasks;
using Xamarin.Forms;

namespace ArcGISRuntime.Samples.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 partial class AnalyzeViewshed : ContentPage
    {

        // Url for the geoprocessing service
        private const string _viewshedUrl =
            "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()
        {
            InitializeComponent();

            // Create the UI, setup the control references and execute initialization
            Initialize();
        }

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

            // Hook into the MapView tapped event
            MyMapView.GeoViewTapped += MyMapView_GeoViewTapped;

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

            // Assign the map to the MapView
            MyMapView.Map = myMap;
        }

        private async void MyMapView_GeoViewTapped(object sender, Esri.ArcGISRuntime.Xamarin.Forms.GeoViewInputEventArgs e)
        {
            // Indicate that the geoprocessing is running
            SetBusy();

            // 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 myInputGraphic = new Graphic(geometry);
            _inputOverlay.Graphics.Add(myInputGraphic);

            // 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)
            {
                await Application.Current.MainPage.DisplayAlert("Error", ex.ToString(), "OK");
            }
        }

        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 myViewshedTask = await GeoprocessingTask.CreateAsync(new Uri(_viewshedUrl));

            // Create a new feature collection table based upon point geometries using the current map view spatial reference
            FeatureCollectionTable myInputFeatures = 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 myInputFeature = myInputFeatures.CreateFeature();

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

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

            // Create the parameters that are passed to the used geoprocessing task
            GeoprocessingParameters myViewshedParameters =
                new GeoprocessingParameters(GeoprocessingExecutionType.SynchronousExecute)
                {

                    // Request the output features to use the same SpatialReference as the map view
                    OutputSpatialReference = MyMapView.SpatialReference
                };

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

            // Create the job that handles the communication between the application and the geoprocessing task
            GeoprocessingJob myViewshedJob = myViewshedTask.CreateJob(myViewshedParameters);

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

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

                // Add all the results as a graphics to the map
                IFeatureSet myViewshedAreas = myViewshedResultFeatures.Features;
                foreach (Feature myFeature in myViewshedAreas)
                {
                    _resultOverlay.Graphics.Add(new Graphic(myFeature.Geometry));
                }
            }
            catch (Exception ex)
            {
                // Display an error message if there is a problem
                if (myViewshedJob.Status == JobStatus.Failed && myViewshedJob.Error != null)
                {
                    await Application.Current.MainPage.DisplayAlert("Geoprocessing error", "Executing geoprocessing failed. " + myViewshedJob.Error.Message, "OK");
                }
                else
                {
                    await Application.Current.MainPage.DisplayAlert("Sample error", "An error occurred. " + ex.ToString(), "OK");
                }
            }
            finally
            {
                // Indicate that the geoprocessing is not running
                SetBusy(false);
            }
        }

        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 myInputRenderer = new SimpleRenderer()
            {
                Symbol = new SimpleMarkerSymbol()
                {
                    Size = 15,
                    Color = System.Drawing.Color.Red
                }
            };

            // Create overlay to where input graphic is shown
            _inputOverlay = new GraphicsOverlay()
            {
                Renderer = myInputRenderer
            };

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

            // Create overlay to where viewshed analysis graphic is shown
            _resultOverlay = new GraphicsOverlay()
            {
                Renderer = myResultRenderer
            };

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

        private void SetBusy(bool isBusy = true)
        {
            // This function toggles running of the 'progress' control feedback status to denote if 
            // the viewshed analysis is executing as a result of the user click on the map

            if (isBusy)
            {
                // Show busy activity indication
                MyActivityIndicator.IsVisible = true;
                MyActivityIndicator.IsRunning = true;
            }
            else
            {
                // Remove the busy activity indication
                MyActivityIndicator.IsRunning = false;
                MyActivityIndicator.IsVisible = false;

            }
        }
    }
}