Display a line of sight

Learn how to perform and display a line of sight analysis in a 3D scene.

display a line of sight

A line of sight analysis is a type of visibility analysis that calculates visibility (visible or obstructed) between a designated observer and target. It calculates whether the target is visible to the observer based on the environment and renders a line indicating visibility on the map.

In this tutorial, you will perform and display a line of sight analysis in a web scene. Your line of sight analysis will show which targets (hot spots) are visible, based on the terrain, from specified observation points in the Yosemite Valley.

Prerequisites

The following are required for this tutorial:

  1. An ArcGIS account to access your API keys. If you don't have an account, sign up for free.
  2. Your system meets the system requirements.

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 project, set your API key.

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.

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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)
        }()
    

Set observer and target symbols

Your app will use graphics to depict the locations of the analyses observer and targets.

  1. Create a private class named Model of type ObservableObject. See the programming patterns page for more information on how to manage states.

  2. Create a GraphicsOverlay named graphicsOverlay and set some of its properties to display the observer and targets graphics.

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    private class Model: ObservableObject {
        // MARK: Graphics
    
        // The graphics overlay to add graphics to.
        let graphicsOverlay: GraphicsOverlay = {
            let graphicsOverlay = GraphicsOverlay()
            graphicsOverlay.sceneProperties.surfacePlacement = .absolute
            graphicsOverlay.sceneProperties.altitudeOffset = 5
            return graphicsOverlay
        }()
    
    
    
    }
    
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  3. Create a private Symbol named observerSymbol with a black fill color and white outline. Create another private symbol named targetSymbol with a white fill color and black outline. These symbols are used to depict the location of the line of sight analyses observer and target respectively. Both symbols will be used to make graphics when the locations are determined.

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    private class Model: ObservableObject {
        // MARK: Graphics
    
        // The graphics overlay to add graphics to.
        let graphicsOverlay: GraphicsOverlay = {
            let graphicsOverlay = GraphicsOverlay()
            graphicsOverlay.sceneProperties.surfacePlacement = .absolute
            graphicsOverlay.sceneProperties.altitudeOffset = 5
            return graphicsOverlay
        }()
    
        // The symbol to indicate the observer.
        private let observerSymbol: Symbol = {
            let symbol = SimpleMarkerSymbol(
                style: .circle,
                color: .black,
                size: 20
            )
            symbol.outline = SimpleLineSymbol(
                style: .solid,
                color: .white,
                width: 2
            )
            return symbol
        }()
    
        // The symbol to indicate the target.
        private var targetSymbol: Symbol = {
            let symbol = SimpleMarkerSymbol(
                style: .circle,
                color: .white,
                size: 20
            )
            symbol.outline = SimpleLineSymbol(
                style: .solid,
                color: .black,
                width: 2
            )
            return symbol
        }()
    
    
    
    }
    
    Expand

Create line of sight analyses

Visual analyses help you make sense of complex 3D data contained by a scene. Use a LocationLineOfSight to perform and display a line of sight analysis using observer and target locations.

  1. Create an AnalysisOverlay named analysisOverlay to contain and display the line of sight analyses.

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        // MARK: Analysis
        // The analysis overlay to be added to the scene.
        let analysisOverlay = AnalysisOverlay()
    
    
    Expand
  2. Create a private variable named observerLocation of type Point.

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        // MARK: Analysis
        // The analysis overlay to be added to the scene.
        let analysisOverlay = AnalysisOverlay()
    
        // The location of the observer.
        private var observerLocation: Point?
    
    
    Expand
  3. Define a private method named createLineOfSight(scenePoint:) that accepts a Point as a parameter. This method creates a LocationLineOfSight analysis, adds it to the scene view analysis overlay, and adds the observer and target graphics to the graphics overlay.

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        // MARK: Analysis
        // The analysis overlay to be added to the scene.
        let analysisOverlay = AnalysisOverlay()
    
        // The location of the observer.
        private var observerLocation: Point?
    
        // Creates the line of sight with the scene point.
        func createLineOfSight(scenePoint: Point) {
    
        }
    
    
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  4. If a line of sight analysis already exists, create a new line of sight analysis using the existing observerLocation and the point. Add the new analysis to the analysis overlay and create and add a target graphic.

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        // MARK: Analysis
        // The analysis overlay to be added to the scene.
        let analysisOverlay = AnalysisOverlay()
    
        // The location of the observer.
        private var observerLocation: Point?
    
        // Creates the line of sight with the scene point.
        func createLineOfSight(scenePoint: Point) {
    
            if let observerLocation {
                // Creates and set initial line of sight analysis with the tapped scene point.
                let lineOfSight = LocationLineOfSight(observerLocation: observerLocation, targetLocation: scenePoint)
                // Adds the line of sight to the analysis overlay.
                analysisOverlay.addAnalysis(lineOfSight)
                // Creates a target graphic and adds it to the graphics overlay.
                let targetGraphic = Graphic(geometry: scenePoint, symbol: targetSymbol)
                graphicsOverlay.addGraphic(targetGraphic)
            }
    
        }
    
    
    Expand
  5. If creating a new line of sight analysis, create a new LocationLineOfSight with the point as the observer and target location. The target location will get a new location upon a secondary tap by the user. Add the new analysis to the analysis overlay with addAnalysis(_:). Lastly, create a graphic for the observer using the observer symbol previously created.

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        // Creates the line of sight with the scene point.
        func createLineOfSight(scenePoint: Point) {
    
            if let observerLocation {
                // Creates and set initial line of sight analysis with the tapped scene point.
                let lineOfSight = LocationLineOfSight(observerLocation: observerLocation, targetLocation: scenePoint)
                // Adds the line of sight to the analysis overlay.
                analysisOverlay.addAnalysis(lineOfSight)
                // Creates a target graphic and adds it to the graphics overlay.
                let targetGraphic = Graphic(geometry: scenePoint, symbol: targetSymbol)
                graphicsOverlay.addGraphic(targetGraphic)
            }
    
            else {
                // Updates the observer location.
                observerLocation = scenePoint
                // Adds the observer graphic to the graphics overlay.
                let observerGraphic = Graphic(geometry: scenePoint, symbol: observerSymbol)
                graphicsOverlay.addGraphic(observerGraphic)
            }
    
        }
    
    Expand
  6. Define a private method named clearAnalyses() to remove all line of sight analyses from the scene view, remove all graphics from the graphics overlay, and set the lineOfSight variable to nil.

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            else {
                // Updates the observer location.
                observerLocation = scenePoint
                // Adds the observer graphic to the graphics overlay.
                let observerGraphic = Graphic(geometry: scenePoint, symbol: observerSymbol)
                graphicsOverlay.addGraphic(observerGraphic)
            }
    
        }
    
        // Resets the observer location and clears all graphics and analyses.
        func clearAnalyses() {
            analysisOverlay.removeAllAnalyses()
            graphicsOverlay.removeAllGraphics()
            observerLocation = nil
        }
    
    Expand

Display the line of sight analyses with touch events

Touch events determine where to place the observer and targets as well as display line of sight analyses. A user taps to place targets and then long-press and drags to place the observer and display line of sight analyses.

  1. The first step to displaying the analyses and graphics is to add the analysis and graphics overlays to the scene view. In the ContentView struct, create a variable of type Model with a @StateObject property wrapper and add the overlays to the scene view.

    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, graphicsOverlays: [model.graphicsOverlay], analysisOverlays: [model.analysisOverlay])
    
        }
    
    }
  2. To add a new line of sight with each tap, add the onSingleTapGesture(perform:) method to the SceneView. In the closure, call the previously created CreateObserverLocation(scenePoint:) method, passing in the scenePoint.

    ContentView.swift
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        var body: some View {
    
            SceneView(scene: scene, graphicsOverlays: [model.graphicsOverlay], analysisOverlays: [model.analysisOverlay])
    
                .onSingleTapGesture { _, scenePoint in
                    // Places an observer point upon single touch.
                    guard let scenePoint else { return }
                    model.createLineOfSight(scenePoint: scenePoint)
                }
    
        }
    
    Expand

Add a UI to control the line of sight analyses

To control the line of sight analyses, some UI is required.

  1. Lastly, create a toolbar and add a "Clear" button to reset the analysis and graphics overlays. The "Clear" button calls the previously created clearAnalyses() method. This will allow users a fresh start to make more analyses.
ContentView.swift
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    var body: some View {

        SceneView(scene: scene, graphicsOverlays: [model.graphicsOverlay], analysisOverlays: [model.analysisOverlay])

            .onSingleTapGesture { _, scenePoint in
                // Places an observer point upon single touch.
                guard let scenePoint else { return }
                model.createLineOfSight(scenePoint: scenePoint)
            }

            .toolbar {
                ToolbarItemGroup(placement: .bottomBar) {
                    Button("Clear") {
                        // Resets the line of sight.
                        model.clearAnalyses()
                    }
                }
            }

    }
Expand

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 set the location of the observer and tap to add target locations. The application performs and displays line of sight analyses between the observer and its targets.

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