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:

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

Steps

Open the Xcode project

To start this tutorial, first complete the Display a web scene tutorial or download and unzip the solution.
Open the .xcodeproj file in Xcode.

If you downloaded the solution project, set your API key.

An API Key enables access to services, web maps, and web scenes hosted in ArcGIS Online.

Go to your developer dashboard to get your API key. For these tutorials, use your default API key. It is scoped to include all of the services demonstrated in the tutorials.
In Xcode, in the Project Navigator, click AppDelegate.swift.

In the editor, set the APIKey property on the AGSArcGISRuntimeEnvironment with your API key.

AppDelegate.swift
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    func application(_ application: UIApplication,
                     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Note: it is not best practice to store API keys in source code.
        // The API key is referenced here for the convenience of this tutorial.

        AGSArcGISRuntimeEnvironment.apiKey = "YOUR_API_KEY"

        return true
    }
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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.

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.
Make a note of the item ID at the end of the browser's URL.
The item ID should be 7558ee942b2547019f66885c44d4f0b1

Update the scene

In Xcode, in the Project Navigator, click ViewController.swift.

In the editor, modify the setupScene() method to create an AGSScene for the web scene. To do this, create a portal item providing the web scene's item ID and an AGSPortal referencing ArcGIS Online.

ViewController.swift
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    private func setupScene() {
        let scene: AGSScene = {
            let portal = AGSPortal.arcGISOnline(withLoginRequired: false)

            let item = AGSPortalItem(portal: portal, itemID: "7558ee942b2547019f66885c44d4f0b1")

            return AGSScene(item: item)
        }()
        sceneView.scene = scene

    }
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Add a UI to control the line of sight analyses

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

Define a private method named setupUI(). Create a "Clear" button and assign it to the navigation bar. The clear button will remove the line of sight analyses from the scene.

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    private func setupUI() {
        let clear = UIBarButtonItem(title: "Clear", style: .plain, target: self, action: #selector(clearScene))
        navigationItem.rightBarButtonItem = clear
    }

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Define a method named clearScene(_:) and assign it the @objc keyword. This method removes the line of sight analyses from the scene view.

The @objc method keyword exposes the method to Objective-C, a necessary step for using the UIBarButtonItem API.

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    private func setupUI() {
        let clear = UIBarButtonItem(title: "Clear", style: .plain, target: self, action: #selector(clearScene))
        navigationItem.rightBarButtonItem = clear
    }

    @objc
    func clearScene(_ sender: UIBarButtonItem) {
        clearAnalyses()
    }
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In viewDidLoad(), call setupUI().

ViewController.swift
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    override func viewDidLoad() {
        super.viewDidLoad()
        setupScene()

        setupUI()

    }
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In Xcode, in the Project Navigator, click Main.storyboard.
In the editor, select ViewController. In the menu bar, click Editor > Embed In > Navigation Controller.
Embedding ViewController within a Navigation Controller places a navigation bar at the top of ViewController. The navigation bar contains the UI elements.
To verify that your UI is set up properly, press <Command+R> to run the app. You should see a "Clear" button contained by the navigation bar and the app should load the Yosemite Valley Hotspots web scene.

Add observer and target graphics

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

In Xcode, in the Project navigator, click ViewController.swift.

Create a private AGSGraphicsOverlay named graphicsOverlay to display the observer and targets graphics.

A graphics overlay is a container for graphics. It is used with a scene view to display graphics on a scene. You can add more than one graphics overlay to a scene view. Graphics overlays are displayed on top of all the other layers.

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    private let graphicsOverlay = AGSGraphicsOverlay()

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Create a private AGSGraphic named observerGraphic with a black fill color and white outline. This graphic is used to depict the location of the line of sight analyses observer and is initialized with a nil geometry because the observer's location is not yet determined.

A graphic with nil geometry will not be rendered in the scene view, even if it has been added to a graphics overlay.

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    private let graphicsOverlay = AGSGraphicsOverlay()

    private let observerGraphic: AGSGraphic = {
        let symbol = AGSSimpleMarkerSymbol(style: .circle, color: .black, size: 16)
        symbol.outline = AGSSimpleLineSymbol(style: .solid, color: .white, width: 2)
        return AGSGraphic(geometry: nil, symbol: symbol)
    }()
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Create a private method named addTargetGraphic(point:) that accepts an AGSPoint as a parameter. This method is used to create graphics with a white fill color and black outline to depict the locations of line of sight analyses targets.

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    private let observerGraphic: AGSGraphic = {
        let symbol = AGSSimpleMarkerSymbol(style: .circle, color: .black, size: 16)
        symbol.outline = AGSSimpleLineSymbol(style: .solid, color: .white, width: 2)
        return AGSGraphic(geometry: nil, symbol: symbol)
    }()

    @discardableResult
    private func addTargetGraphic(point: AGSPoint) -> AGSGraphic {
        let symbol = AGSSimpleMarkerSymbol(style: .circle, color: .white, size: 16)
        symbol.outline = AGSSimpleLineSymbol(style: .solid, color: .black, width: 2)
        let targetGraphic = AGSGraphic(geometry: point, symbol: symbol, attributes: nil)
        graphicsOverlay.graphics.add(targetGraphic)
        return targetGraphic
    }
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Create a private computed variable named targetGraphics to filter and return all graphics contained by graphicsOverlay that depict target locations. The graphics overlay contains one observerGraphic and zero or several target graphics so any graphic that is not the observer is a target.

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    @discardableResult
    private func addTargetGraphic(point: AGSPoint) -> AGSGraphic {
        let symbol = AGSSimpleMarkerSymbol(style: .circle, color: .white, size: 16)
        symbol.outline = AGSSimpleLineSymbol(style: .solid, color: .black, width: 2)
        let targetGraphic = AGSGraphic(geometry: point, symbol: symbol, attributes: nil)
        graphicsOverlay.graphics.add(targetGraphic)
        return targetGraphic
    }

    private var targetGraphics: [AGSGraphic] {
        graphicsOverlay.graphics.filter { ($0 as! AGSGraphic) != observerGraphic } as! [AGSGraphic]
    }
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Define a private method named setupGraphicsOverlay() to specify various sceneProperties of the graphicsOverlay and add it to the scene view. Scene properties of the graphics overlay allow you to control 3D-specific rendering of graphics.

Specifying the surfacePlacement as absolute treats graphics geometry z-values as absolute altitude values. If the geometry does not contain a z-value or has a value of 0, the graphic will be rendered at surface level. Increasing the z-value renders the graphic at a higher altitude.
Specifying the altitudeOffset increases the altitude by adding the specified value to the z-value altitude.

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    private var targetGraphics: [AGSGraphic] {
        graphicsOverlay.graphics.filter { ($0 as! AGSGraphic) != observerGraphic } as! [AGSGraphic]
    }

    private func setupGraphicsOverlay() {
        graphicsOverlay.graphics.add(observerGraphic)
        graphicsOverlay.sceneProperties?.surfacePlacement = .absolute
        graphicsOverlay.sceneProperties?.altitudeOffset = 5
        sceneView.graphicsOverlays.add(graphicsOverlay)
    }
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In viewDidLoad(), call the method setupGraphicsOverlay().

ViewController.swift
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    override func viewDidLoad() {
        super.viewDidLoad()
        setupScene()

        setupUI()

        setupGraphicsOverlay()

    }
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Create line of sight analyses

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

Create a private AGSAnalysisOverlay named analysisOverlay to contain and display the line of sight analyses.

An analysis overlay is a container for analyses. 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 let analysisOverlay = AGSAnalysisOverlay()

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Define a private method named setupAnalysisOverlay() to add the analysis overlay to the scene view.

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    private let analysisOverlay = AGSAnalysisOverlay()

    private func setupAnalysisOverlay() {
        sceneView.analysisOverlays.add(analysisOverlay)
    }
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In viewDidLoad(), call the method setupAnalysisOverlay().

ViewController.swift
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    override func viewDidLoad() {
        super.viewDidLoad()
        setupScene()

        setupUI()

        setupGraphicsOverlay()

        setupAnalysisOverlay()

    }
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Define a private method named createLineOfSightAnalysis(observer:target:) that accepts an observer and a target as parameters, both are AGSGeoElement types. This method creates a AGSGeoElementLineOfSight analysis and adds it to the scene view analysis overlay.

A AGSGeoElementLineOfSight is used to perform and display a line of sight analysis between two AGSGeoElement types, like a feature or graphic. Alternatively, you can perform and display a line of sight analysis between two locations (3D points) using a AGSLocationLineOfSight.

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    private func setupAnalysisOverlay() {
        sceneView.analysisOverlays.add(analysisOverlay)
    }

    private func createLineOfSightAnalysis(observer: AGSGeoElement, target: AGSGeoElement) {
        let line = AGSGeoElementLineOfSight(observerGeoElement: observer, targetGeoElement: target)
        analysisOverlay.analyses.add(line)
    }
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Define a private method named clearAnalyses() to remove all line of sight analyses from the scene view. This method also removes observer and target graphics.

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    private func createLineOfSightAnalysis(observer: AGSGeoElement, target: AGSGeoElement) {
        let line = AGSGeoElementLineOfSight(observerGeoElement: observer, targetGeoElement: target)
        analysisOverlay.analyses.add(line)
    }

    private func clearAnalyses() {
        analysisOverlay.analyses.removeAllObjects()
        observerGraphic.geometry = nil
        graphicsOverlay.graphics.removeObjects(in: targetGraphics)
    }
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Define a private method named setObserver(point:) that accepts an AGSPoint as a parameter. This method is used to specify the location of observerGraphic and create line of sight analyses for targets, if they exist.

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    private func clearAnalyses() {
        analysisOverlay.analyses.removeAllObjects()
        observerGraphic.geometry = nil
        graphicsOverlay.graphics.removeObjects(in: targetGraphics)
    }

    private func setObserver(point: AGSPoint) {
        let shouldCreateAnalyses = observerGraphic.geometry == nil
        observerGraphic.geometry = point
        if shouldCreateAnalyses {
            targetGraphics.forEach { targetGraphic in
                createLineOfSightAnalysis(observer: observerGraphic, target: targetGraphic)
            }
        }
    }
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Define a private method named clearObserver() to remove the observer.
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