Display a viewshed

Learn how to perform and display a viewshed analysis in a 3D scene.

Viewshed analysis determines the visibility of terrain, buildings, and other 3D objects from an observer's location within a scene (using a specified field of view). The result indicates which areas are visible and which are obstructed when viewed from the observer's perspective.

In this tutorial, you will perform and display a viewshed analysis in a web scene. Your viewshed analysis will show visibility (visible or obstructed) and can be used to determine which hotspots in the Yosemite Valley are visible from a specified observer's perspective.

Prerequisites

Steps

Open the Xcode project

1. To start this tutorial, first complete the Display a web scene tutorial or download and unzip the solution.

2. Open the .xcodeproj file in Xcode.

3. If you downloaded the solution, get an access token and set the API key.

   More info

   An API Key gives your app access to secure resources used in this tutorial.

   1. Go to the Create an API key tutorial to obtain a new API key access token using your ArcGIS Location Platform or ArcGIS Online account. Ensure that the following privilege is enabled: Location services > Basemaps > Basemap styles service. Copy the access token as it will be used in the next step.

   2. In Xcode, in the Project Navigator, click MainApp.swift.

   3. In the Editor, set the ArcGISEnvironment.apiKey property on the ArcGISEnvironment with your access token.

      MainApp.swift

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          init() {
              ArcGISEnvironment.apiKey = APIKey("<#YOUR-ACCESS-TOKEN#>")
          }
      

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Get the web scene item ID

You can use ArcGIS tools to create and view web scenes. Use the Scene Viewer to identify the web scene item ID. This item ID will be used later in the tutorial.

1. Go to the Yosemite Valley Hotspots web scene in the Scene Viewer in ArcGIS Online. This web scene displays terrain and hotspots in the Yosemite Valley.
2. Make a note of the item ID at the end of the browser's URL. The item ID should be 7558ee942b2547019f66885c44d4f0b1.

Update the scene

1. In Xcode, in the Project Navigator, click ContentView.swift.

2. In the editor, modify the scene variable to create a Scene for the web scene. To do this, create a portal item providing the web scene's item ID and a Portal referencing ArcGIS Online.

   ContentView.swift

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       // The Yosemite Valley hotspots scene.
       @State private var scene: ArcGIS.Scene = {
   
           let portalItem = PortalItem(
               portal: .arcGISOnline(connection: .anonymous),
               id: Item.ID("7558ee942b2547019f66885c44d4f0b1")!
           )
   
           return Scene(item: portalItem)
       }()
   

Create a viewshed analysis

Visual analyses are used to help you make sense of complex 3D data contained by a scene. Use a LocationViewshed to perform and display a viewshed analysis using a 3D point to define the observer's location.

1. Create a private class named Model of type ObservableObject and an accompanying State Object reference in the ContentView struct. See the programming patterns page for more information on how to manage states.

   ContentView.swift

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   import SwiftUI
   import ArcGIS
   
   private class Model: ObservableObject {
   
   }
   
   struct ContentView: View {
   
       // An ObservableObject containing the scene, graphics overlay, and analysis overlay.
       @StateObject private var model = Model()
   
       // The Yosemite Valley hotspots scene.
       @State private var scene: ArcGIS.Scene = {
   
           let portalItem = PortalItem(
               portal: .arcGISOnline(connection: .anonymous),
               id: Item.ID("7558ee942b2547019f66885c44d4f0b1")!
           )
   
           return Scene(item: portalItem)
       }()
   

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2. Create an AnalysisOverlay named analysisOverlay to contain and display the viewshed analyses.

   More info

   An analysis overlay is a container for Analysis objects. It is used with a scene view to display visual analyses on a scene. You can add more than one analysis overlay to a scene view. Analysis overlays are displayed on top of all other layers and graphics overlays.

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   private class Model: ObservableObject {
   
       // The analysis overlay to be added to the scene.
       let analysisOverlay = AnalysisOverlay()
   
   }
   

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3. Create a private LocationViewshed named viewshed.

   More info

   The viewshed analysis is added to a scene view using an analysis overlay. An analysis overlay is a container for analyses. It can be used to display visual analyses in a scene view. You can add more than one analysis overlay and they are displayed on top of all other layers.

   ContentView.swift

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   private class Model: ObservableObject {
   
       // The analysis overlay to be added to the scene.
       let analysisOverlay = AnalysisOverlay()
   
       let viewshed: LocationViewshed
   
   }
   

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4. Create a Double variable named maxDistance to track the viewshed's maximum distance. Set the viewshed's maxDistance property to the model's maxDistance property in a didSet observer to update the maximum distance when needed.

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   private class Model: ObservableObject {
   
       // The analysis overlay to be added to the scene.
       let analysisOverlay = AnalysisOverlay()
   
       let viewshed: LocationViewshed
   
       var maxDistance: Double {
           didSet {
               viewshed.maxDistance = maxDistance
           }
       }
   
   }
   

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5. In init(), initialize all of the properties, make the viewshed not visible upon launch, and add the viewshed to the analysis overlay.

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   private class Model: ObservableObject {
   
       // The analysis overlay to be added to the scene.
       let analysisOverlay = AnalysisOverlay()
   
       let viewshed: LocationViewshed
   
       var maxDistance: Double {
           didSet {
               viewshed.maxDistance = maxDistance
           }
       }
   
       init() {
           self.viewshed = LocationViewshed(
               location: Point(latitude: 0, longitude: 0),
               heading: 0,
               pitch: 90,
               horizontalAngle: 360,
               verticalAngle: 180,
               minDistance: 10,
               maxDistance: 12_000
           )
           viewshed.isVisible = false
           analysisOverlay.addAnalysis(viewshed)
           maxDistance = viewshed.maxDistance!
       }
   
   }
   

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6. Define a private method named setViewshedLocation(point:) that receives a point as a parameter. This method is used to set the location of the viewshed and make it visible, if it is not visible already.

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       func setViewshedLocation(point: Point) {
           viewshed.location = point
           if !viewshed.isVisible {
               viewshed.isVisible = true
           }
       }
   
   }
   

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7. Define a private method named hideViewshed(). This method is used to hide the viewshed.

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       func setViewshedLocation(point: Point) {
           viewshed.location = point
           if !viewshed.isVisible {
               viewshed.isVisible = true
           }
       }
   
       func hideViewshed() {
           viewshed.isVisible = false
       }
   
   }
   

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Display the viewshed analysis with touch events

Touch events determine where to place the observer for the viewshed analysis. A user will long-press and drag to reveal and move the observer's location.

1. The first step to displaying the analyses is to add the analysis overlay to the scene view. In the ContentView struct, modify the scene view to add the model's analysis overlay.

   ContentView.swift

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   struct ContentView: View {
   
       // An ObservableObject containing the scene, graphics overlay, and analysis overlay.
       @StateObject private var model = Model()
   
       // The Yosemite Valley hotspots scene.
       @State private var scene: ArcGIS.Scene = {
   
           let portalItem = PortalItem(
               portal: .arcGISOnline(connection: .anonymous),
               id: Item.ID("7558ee942b2547019f66885c44d4f0b1")!
           )
   
           return Scene(item: portalItem)
       }()
   
       var body: some View {
   
           SceneView(scene: scene, analysisOverlays: [model.analysisOverlay])
   
       }
   
   }

2. To add or move the viewshed analysis upon long press and drag, add the onLongPressGesture(perform:) method to the SceneView. In the closure, call the previously created setViewshedLocation(point:) method, passing in the scenePoint.

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       var body: some View {
   
           SceneView(scene: scene, analysisOverlays: [model.analysisOverlay])
   
               .onLongPressGesture { _, scenePoint in
                   guard let scenePoint = scenePoint else { return }
                   model.setViewshedLocation(point: scenePoint)
               }
   
       }
   

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Add a UI to control the viewshed analysis

To control the viewshed analysis, some UI elements are required.

1. Add a toolbar to the bottom of the scene view.

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   Add line.Add line.Add line.Add line.Add line.

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       var body: some View {
   
           SceneView(scene: scene, analysisOverlays: [model.analysisOverlay])
   
               .onLongPressGesture { _, scenePoint in
                   guard let scenePoint = scenePoint else { return }
                   model.setViewshedLocation(point: scenePoint)
               }
   
               .toolbar {
                   ToolbarItemGroup(placement: .bottomBar) {
   
                   }
               }
   
       }
   

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2. Add a Slider named slider to the toolbar with the model's maxDistance property as its value and 10...12_000 as the range. The slider changes the viewshed's maximum distance by expanding or contracting the size of the observer's field of view. The maximumValue and minimumValue properties define the range of values the user can select to calculate the viewshed. You set an action on the slider using a selector for a method that will be added in a later step.

   ContentView.swift

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               .toolbar {
                   ToolbarItemGroup(placement: .bottomBar) {
   
                       Slider(value: $model.maxDistance, in: 10...12_000)
                           .frame(width: 300)
   
                   }
               }
   

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3. Lastly, create a toolbar and add a "Clear" button to reset the analysis overlay. The "Clear" button calls the previously created hideViewshed() method. This will allow users a fresh start to make more analyses.

   ContentView.swift

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               .toolbar {
                   ToolbarItemGroup(placement: .bottomBar) {
   
                       Slider(value: $model.maxDistance, in: 10...12_000)
                           .frame(width: 300)
   
                       Spacer()
                       Button("Clear") {
                           // Resets the line of sight.
                           model.hideViewshed()
                       }
   
                   }
               }
   

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Run the app

Press Command + R to run the app.

You should see a scene of hotspots in the Yosemite Valley. Long-press and drag to display and move a viewshed analysis to explore the visibility of terrain from various locations.

What's next?

Learn how to use additional API features, ArcGIS location services, and ArcGIS tools in these tutorials:

• Display a line of sight