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

Before starting this tutorial:

You need an ArcGIS Location Platform or ArcGIS Online account.
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, get an access token and set the API key.
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. 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 AppDelegate.swift.
3. In the editor, set the APIKey property on the AGSArcGISRuntimeEnvironment with your access token.
  AppDelegate.swift
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  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool { AGSArcGISRuntimeEnvironment.apiKey = "YOUR_ACCESS_TOKEN" return true }
  Expand
  Warning
  The access token is stored directly in the code as a convenience for this tutorial. Storing access tokens in the source code is not best practice.

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.

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Change line    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 viewshed analysis

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

Create a private UISlider named slider. 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.

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Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.    private lazy var slider: UISlider = {
        let slider = UISlider()
        slider.maximumValue = 12_000
        slider.minimumValue = 1_000
        slider.value = 3_000
        slider.addTarget(self, action: #selector(sliderValueDidChange), for: .allTouchEvents)
        return slider
    }()

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Define a private method named setupUI() and assign the slider as well as a "Clear" button to the navigation bar. The clear button removes the viewshed from the scene. You set an action on the clear button using a selector for a method that will be added in a later step.

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        let slider = UISlider()
        slider.maximumValue = 12_000
        slider.minimumValue = 1_000
        slider.value = 3_000
        slider.addTarget(self, action: #selector(sliderValueDidChange), for: .allTouchEvents)
        return slider
    }()

    private func setupUI() {
        navigationItem.titleView = slider
        navigationItem.rightBarButtonItem = UIBarButtonItem(
            title: "Clear",
            style: .plain,
            target: self,
            action: #selector(clearScene)
        )
    }
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Define a method named sliderValueDidChange(_:) and assign it the @objc keyword. This method updates the viewshed's maxDistance to a value specified by the slider. The @objc method keyword exposes the method to Objective-C, a necessary step for using the UISlider API.

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        navigationItem.titleView = slider
        navigationItem.rightBarButtonItem = UIBarButtonItem(
            title: "Clear",
            style: .plain,
            target: self,
            action: #selector(clearScene)
        )
    }

    @objc
    func sliderValueDidChange(_ sender: UISlider) {
        viewshed.maxDistance = Double(sender.value)
    }
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Define a method named clearScene(_:) and assign it the @objc keyword. This method hides the viewshed 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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    func sliderValueDidChange(_ sender: UISlider) {
        viewshed.maxDistance = Double(sender.value)
    }

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

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        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 slider and a "Clear" button contained by the navigation bar and the app should load the Yosemite Valley Hotspots web scene.

Create a viewshed analysis

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

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

In the editor, create a private lazy AGSLocationViewshed named viewshed. Upon launch, the viewshed should not be visible.

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        let viewshed = AGSLocationViewshed(
            location: AGSPointMake3D(0, 0, 0, 0, .wgs84()),
            heading: 0,
            pitch: 90,
            horizontalAngle: 360,
            verticalAngle: 180,
            minDistance: 10,
            maxDistance: Double(slider.value)
        )
        viewshed.isVisible = false
        return viewshed
    }()

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Define a private method named setupAnalysisOverlay() to add the viewshed to the scene.

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.

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        let viewshed = AGSLocationViewshed(
            location: AGSPointMake3D(0, 0, 0, 0, .wgs84()),
            heading: 0,
            pitch: 90,
            horizontalAngle: 360,
            verticalAngle: 180,
            minDistance: 10,
            maxDistance: Double(slider.value)
        )
        viewshed.isVisible = false
        return viewshed
    }()

    private func setupAnalysisOverlay() {
        let analysisOverlay = AGSAnalysisOverlay()
        sceneView.analysisOverlays.add(analysisOverlay)
        analysisOverlay.analyses.add(viewshed)
    }
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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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        let analysisOverlay = AGSAnalysisOverlay()
        sceneView.analysisOverlays.add(analysisOverlay)
        analysisOverlay.analyses.add(viewshed)
    }

    private func setViewshedLocation(point: AGSPoint) {
        viewshed.location = point
        if !viewshed.isVisible {
            viewshed.isVisible = true
        }
    }
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Define a private method named clearViewshed(). This method is used to hide the viewshed.

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        viewshed.location = point
        if !viewshed.isVisible {
            viewshed.isVisible = true
        }
    }

    private func clearViewshed() {
        viewshed.isVisible = false
    }
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In viewDidLoad(), call setupAnalysisOverlay().

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        super.viewDidLoad()
        setupScene()

        setupUI()

        setupAnalysisOverlay()

    }
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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.

Extend ViewController to conform to the AGSGeoViewTouchDelegate protocol and include the four long-press geoview touch delegate methods.

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Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.Add line.extension ViewController: AGSGeoViewTouchDelegate {

    func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {

    }

    func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {

    }

    func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {

    }

    func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {

    }

}

When the user begins, moves, and ends a long-press touch event, call setViewshedLocation(point:). Using all three touch delegate methods together allows the user to reveal the observer location with a long-press touch event and move the observer by dragging their finger around the screen.

ViewController.swift
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Add line.Add line.Add line.extension ViewController: AGSGeoViewTouchDelegate {

    func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {

        setViewshedLocation(point: mapPoint)

    }

    func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {

        setViewshedLocation(point: mapPoint)

    }

    func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {

        setViewshedLocation(point: mapPoint)

    }

    func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {

    }

}

When the user cancels the long-press touch event, call clearViewshed().

This may happen, for instance, when you have the magnifier visible and attempt to take a screenshot using the home/lock button combination.

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Add line.extension ViewController: AGSGeoViewTouchDelegate {

    func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {

        setViewshedLocation(point: mapPoint)

    }

    func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {

        setViewshedLocation(point: mapPoint)

    }

    func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {

        setViewshedLocation(point: mapPoint)

    }

    func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {

        clearViewshed()

    }

}

In the setupScene() method, assign ViewController to sceneView.touchDelegate.

This step bridges sceneView user touch interactions with ViewController via the AGSGeoViewTouchDelegate protocol.

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Add line.    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

        sceneView.touchDelegate = self

    }
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Run the app

Press Command + R to run the app.

If you are using the Xcode simulator your system must meet these minimum requirements: macOS Big Sur 11.3, Xcode 13, iOS 13. If you are using a physical device, then refer to the system requirements.

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: