Display a line of sight

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

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

Steps

Open an Xcode project

This tutorial uses the completed Display a web scene tutorial as a starting point. You can first complete that tutorial or download and unzip the completed solution.

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.

Set the API Key

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

1. 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.

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

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

   
   
   AppDelegate.swift

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   // Copyright 2021 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
   //
   //   https://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.
   
   
   import UIKit
   
   import ArcGIS
   
   
   @UIApplicationMain
   class AppDelegate: UIResponder, UIApplicationDelegate {
       var window: UIWindow?
   
       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.

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 ViewController.swift.

2. 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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   // Copyright 2021 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.
   
   import ArcGIS
   
   class ViewController: UIViewController {
       @IBOutlet weak var sceneView: AGSSceneView!
   
       override func viewDidLoad() {
           super.viewDidLoad()
           setupScene()
   
           setupUI()
   
           setupGraphicsOverlay()
   
           setupAnalysisOverlay()
   
       }
   
       // MARK: Scene
   
       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
   
       }
   
       // MARK: UI
   
       private func setupUI() {
           let clear = UIBarButtonItem(title: "Clear", style: .plain, target: self, action: #selector(clearScene))
           navigationItem.rightBarButtonItem = clear
       }
   
       @objc
       func clearScene(_ sender: UIBarButtonItem) {
           clearAnalyses()
       }
   
       // MARK: Graphics
   
       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)
       }()
   
       @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]
       }
   
       private func setupGraphicsOverlay() {
           graphicsOverlay.graphics.add(observerGraphic)
           graphicsOverlay.sceneProperties?.surfacePlacement = .absolute
           graphicsOverlay.sceneProperties?.altitudeOffset = 5
           sceneView.graphicsOverlays.add(graphicsOverlay)
       }
   
       // MARK: Line of Sight Analysis
   
       private let analysisOverlay = AGSAnalysisOverlay()
   
       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)
       }
   
       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)
               }
           }
       }
   
       private func clearObserver() {
           analysisOverlay.analyses.removeAllObjects()
           observerGraphic.geometry = nil
       }
   
       private func addTarget(point: AGSPoint) {
           let targetGraphic = addTargetGraphic(point: point)
           if observerGraphic.geometry != nil {
               createLineOfSightAnalysis(observer: observerGraphic, target: targetGraphic)
           }
       }
   
   }
   
   // MARK: - GeoView Touch Delegate
   
   extension ViewController: AGSGeoViewTouchDelegate {
   
       func geoView(_ geoView: AGSGeoView, didTapAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           addTarget(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {
   
           clearObserver()
   
       }
   
   }
   

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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.

1. 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.

   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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   // Copyright 2021 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.
   
   import ArcGIS
   
   class ViewController: UIViewController {
       @IBOutlet weak var sceneView: AGSSceneView!
   
       override func viewDidLoad() {
           super.viewDidLoad()
           setupScene()
   
           setupUI()
   
           setupGraphicsOverlay()
   
           setupAnalysisOverlay()
   
       }
   
       // MARK: Scene
   
       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
   
       }
   
       // MARK: UI
   
       private func setupUI() {
           let clear = UIBarButtonItem(title: "Clear", style: .plain, target: self, action: #selector(clearScene))
           navigationItem.rightBarButtonItem = clear
       }
   
       @objc
       func clearScene(_ sender: UIBarButtonItem) {
           clearAnalyses()
       }
   
       // MARK: Graphics
   
       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)
       }()
   
       @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]
       }
   
       private func setupGraphicsOverlay() {
           graphicsOverlay.graphics.add(observerGraphic)
           graphicsOverlay.sceneProperties?.surfacePlacement = .absolute
           graphicsOverlay.sceneProperties?.altitudeOffset = 5
           sceneView.graphicsOverlays.add(graphicsOverlay)
       }
   
       // MARK: Line of Sight Analysis
   
       private let analysisOverlay = AGSAnalysisOverlay()
   
       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)
       }
   
       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)
               }
           }
       }
   
       private func clearObserver() {
           analysisOverlay.analyses.removeAllObjects()
           observerGraphic.geometry = nil
       }
   
       private func addTarget(point: AGSPoint) {
           let targetGraphic = addTargetGraphic(point: point)
           if observerGraphic.geometry != nil {
               createLineOfSightAnalysis(observer: observerGraphic, target: targetGraphic)
           }
       }
   
   }
   
   // MARK: - GeoView Touch Delegate
   
   extension ViewController: AGSGeoViewTouchDelegate {
   
       func geoView(_ geoView: AGSGeoView, didTapAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           addTarget(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {
   
           clearObserver()
   
       }
   
   }
   

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2. 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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   // Copyright 2021 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.
   
   import ArcGIS
   
   class ViewController: UIViewController {
       @IBOutlet weak var sceneView: AGSSceneView!
   
       override func viewDidLoad() {
           super.viewDidLoad()
           setupScene()
   
           setupUI()
   
           setupGraphicsOverlay()
   
           setupAnalysisOverlay()
   
       }
   
       // MARK: Scene
   
       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
   
       }
   
       // MARK: UI
   
       private func setupUI() {
           let clear = UIBarButtonItem(title: "Clear", style: .plain, target: self, action: #selector(clearScene))
           navigationItem.rightBarButtonItem = clear
       }
   
       @objc
       func clearScene(_ sender: UIBarButtonItem) {
           clearAnalyses()
       }
   
       // MARK: Graphics
   
       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)
       }()
   
       @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]
       }
   
       private func setupGraphicsOverlay() {
           graphicsOverlay.graphics.add(observerGraphic)
           graphicsOverlay.sceneProperties?.surfacePlacement = .absolute
           graphicsOverlay.sceneProperties?.altitudeOffset = 5
           sceneView.graphicsOverlays.add(graphicsOverlay)
       }
   
       // MARK: Line of Sight Analysis
   
       private let analysisOverlay = AGSAnalysisOverlay()
   
       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)
       }
   
       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)
               }
           }
       }
   
       private func clearObserver() {
           analysisOverlay.analyses.removeAllObjects()
           observerGraphic.geometry = nil
       }
   
       private func addTarget(point: AGSPoint) {
           let targetGraphic = addTargetGraphic(point: point)
           if observerGraphic.geometry != nil {
               createLineOfSightAnalysis(observer: observerGraphic, target: targetGraphic)
           }
       }
   
   }
   
   // MARK: - GeoView Touch Delegate
   
   extension ViewController: AGSGeoViewTouchDelegate {
   
       func geoView(_ geoView: AGSGeoView, didTapAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           addTarget(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {
   
           clearObserver()
   
       }
   
   }
   

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3. In viewDidLoad(), call setupUI().

   ViewController.swift

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   // Copyright 2021 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.
   
   import ArcGIS
   
   class ViewController: UIViewController {
       @IBOutlet weak var sceneView: AGSSceneView!
   
       override func viewDidLoad() {
           super.viewDidLoad()
           setupScene()
   
           setupUI()
   
           setupGraphicsOverlay()
   
           setupAnalysisOverlay()
   
       }
   
       // MARK: Scene
   
       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
   
       }
   
       // MARK: UI
   
       private func setupUI() {
           let clear = UIBarButtonItem(title: "Clear", style: .plain, target: self, action: #selector(clearScene))
           navigationItem.rightBarButtonItem = clear
       }
   
       @objc
       func clearScene(_ sender: UIBarButtonItem) {
           clearAnalyses()
       }
   
       // MARK: Graphics
   
       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)
       }()
   
       @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]
       }
   
       private func setupGraphicsOverlay() {
           graphicsOverlay.graphics.add(observerGraphic)
           graphicsOverlay.sceneProperties?.surfacePlacement = .absolute
           graphicsOverlay.sceneProperties?.altitudeOffset = 5
           sceneView.graphicsOverlays.add(graphicsOverlay)
       }
   
       // MARK: Line of Sight Analysis
   
       private let analysisOverlay = AGSAnalysisOverlay()
   
       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)
       }
   
       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)
               }
           }
       }
   
       private func clearObserver() {
           analysisOverlay.analyses.removeAllObjects()
           observerGraphic.geometry = nil
       }
   
       private func addTarget(point: AGSPoint) {
           let targetGraphic = addTargetGraphic(point: point)
           if observerGraphic.geometry != nil {
               createLineOfSightAnalysis(observer: observerGraphic, target: targetGraphic)
           }
       }
   
   }
   
   // MARK: - GeoView Touch Delegate
   
   extension ViewController: AGSGeoViewTouchDelegate {
   
       func geoView(_ geoView: AGSGeoView, didTapAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           addTarget(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {
   
           clearObserver()
   
       }
   
   }
   

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4. In Xcode, in the Project Navigator, click Main.storyboard.

5. In the editor, select ViewController. In the menu bar, click Editor > Embed In > Navigation Controller.

   More info

   Embedding ViewController within a Navigation Controller places a navigation bar at the top of ViewController. The navigation bar contains the UI elements.

6. 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.

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

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

   More info

   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.

   ViewController.swift

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   // Copyright 2021 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.
   
   import ArcGIS
   
   class ViewController: UIViewController {
       @IBOutlet weak var sceneView: AGSSceneView!
   
       override func viewDidLoad() {
           super.viewDidLoad()
           setupScene()
   
           setupUI()
   
           setupGraphicsOverlay()
   
           setupAnalysisOverlay()
   
       }
   
       // MARK: Scene
   
       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
   
       }
   
       // MARK: UI
   
       private func setupUI() {
           let clear = UIBarButtonItem(title: "Clear", style: .plain, target: self, action: #selector(clearScene))
           navigationItem.rightBarButtonItem = clear
       }
   
       @objc
       func clearScene(_ sender: UIBarButtonItem) {
           clearAnalyses()
       }
   
       // MARK: Graphics
   
       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)
       }()
   
       @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]
       }
   
       private func setupGraphicsOverlay() {
           graphicsOverlay.graphics.add(observerGraphic)
           graphicsOverlay.sceneProperties?.surfacePlacement = .absolute
           graphicsOverlay.sceneProperties?.altitudeOffset = 5
           sceneView.graphicsOverlays.add(graphicsOverlay)
       }
   
       // MARK: Line of Sight Analysis
   
       private let analysisOverlay = AGSAnalysisOverlay()
   
       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)
       }
   
       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)
               }
           }
       }
   
       private func clearObserver() {
           analysisOverlay.analyses.removeAllObjects()
           observerGraphic.geometry = nil
       }
   
       private func addTarget(point: AGSPoint) {
           let targetGraphic = addTargetGraphic(point: point)
           if observerGraphic.geometry != nil {
               createLineOfSightAnalysis(observer: observerGraphic, target: targetGraphic)
           }
       }
   
   }
   
   // MARK: - GeoView Touch Delegate
   
   extension ViewController: AGSGeoViewTouchDelegate {
   
       func geoView(_ geoView: AGSGeoView, didTapAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           addTarget(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {
   
           clearObserver()
   
       }
   
   }
   

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3. 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.

   More info

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

   ViewController.swift

   Use dark colors for code blocks

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

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   // Copyright 2021 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.
   
   import ArcGIS
   
   class ViewController: UIViewController {
       @IBOutlet weak var sceneView: AGSSceneView!
   
       override func viewDidLoad() {
           super.viewDidLoad()
           setupScene()
   
           setupUI()
   
           setupGraphicsOverlay()
   
           setupAnalysisOverlay()
   
       }
   
       // MARK: Scene
   
       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
   
       }
   
       // MARK: UI
   
       private func setupUI() {
           let clear = UIBarButtonItem(title: "Clear", style: .plain, target: self, action: #selector(clearScene))
           navigationItem.rightBarButtonItem = clear
       }
   
       @objc
       func clearScene(_ sender: UIBarButtonItem) {
           clearAnalyses()
       }
   
       // MARK: Graphics
   
       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)
       }()
   
       @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]
       }
   
       private func setupGraphicsOverlay() {
           graphicsOverlay.graphics.add(observerGraphic)
           graphicsOverlay.sceneProperties?.surfacePlacement = .absolute
           graphicsOverlay.sceneProperties?.altitudeOffset = 5
           sceneView.graphicsOverlays.add(graphicsOverlay)
       }
   
       // MARK: Line of Sight Analysis
   
       private let analysisOverlay = AGSAnalysisOverlay()
   
       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)
       }
   
       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)
               }
           }
       }
   
       private func clearObserver() {
           analysisOverlay.analyses.removeAllObjects()
           observerGraphic.geometry = nil
       }
   
       private func addTarget(point: AGSPoint) {
           let targetGraphic = addTargetGraphic(point: point)
           if observerGraphic.geometry != nil {
               createLineOfSightAnalysis(observer: observerGraphic, target: targetGraphic)
           }
       }
   
   }
   
   // MARK: - GeoView Touch Delegate
   
   extension ViewController: AGSGeoViewTouchDelegate {
   
       func geoView(_ geoView: AGSGeoView, didTapAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           addTarget(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {
   
           clearObserver()
   
       }
   
   }
   

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4. 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.

   ViewController.swift

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   // Copyright 2021 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.
   
   import ArcGIS
   
   class ViewController: UIViewController {
       @IBOutlet weak var sceneView: AGSSceneView!
   
       override func viewDidLoad() {
           super.viewDidLoad()
           setupScene()
   
           setupUI()
   
           setupGraphicsOverlay()
   
           setupAnalysisOverlay()
   
       }
   
       // MARK: Scene
   
       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
   
       }
   
       // MARK: UI
   
       private func setupUI() {
           let clear = UIBarButtonItem(title: "Clear", style: .plain, target: self, action: #selector(clearScene))
           navigationItem.rightBarButtonItem = clear
       }
   
       @objc
       func clearScene(_ sender: UIBarButtonItem) {
           clearAnalyses()
       }
   
       // MARK: Graphics
   
       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)
       }()
   
       @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]
       }
   
       private func setupGraphicsOverlay() {
           graphicsOverlay.graphics.add(observerGraphic)
           graphicsOverlay.sceneProperties?.surfacePlacement = .absolute
           graphicsOverlay.sceneProperties?.altitudeOffset = 5
           sceneView.graphicsOverlays.add(graphicsOverlay)
       }
   
       // MARK: Line of Sight Analysis
   
       private let analysisOverlay = AGSAnalysisOverlay()
   
       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)
       }
   
       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)
               }
           }
       }
   
       private func clearObserver() {
           analysisOverlay.analyses.removeAllObjects()
           observerGraphic.geometry = nil
       }
   
       private func addTarget(point: AGSPoint) {
           let targetGraphic = addTargetGraphic(point: point)
           if observerGraphic.geometry != nil {
               createLineOfSightAnalysis(observer: observerGraphic, target: targetGraphic)
           }
       }
   
   }
   
   // MARK: - GeoView Touch Delegate
   
   extension ViewController: AGSGeoViewTouchDelegate {
   
       func geoView(_ geoView: AGSGeoView, didTapAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           addTarget(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {
   
           clearObserver()
   
       }
   
   }
   

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5. 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.

   ViewController.swift

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   // Copyright 2021 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.
   
   import ArcGIS
   
   class ViewController: UIViewController {
       @IBOutlet weak var sceneView: AGSSceneView!
   
       override func viewDidLoad() {
           super.viewDidLoad()
           setupScene()
   
           setupUI()
   
           setupGraphicsOverlay()
   
           setupAnalysisOverlay()
   
       }
   
       // MARK: Scene
   
       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
   
       }
   
       // MARK: UI
   
       private func setupUI() {
           let clear = UIBarButtonItem(title: "Clear", style: .plain, target: self, action: #selector(clearScene))
           navigationItem.rightBarButtonItem = clear
       }
   
       @objc
       func clearScene(_ sender: UIBarButtonItem) {
           clearAnalyses()
       }
   
       // MARK: Graphics
   
       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)
       }()
   
       @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]
       }
   
       private func setupGraphicsOverlay() {
           graphicsOverlay.graphics.add(observerGraphic)
           graphicsOverlay.sceneProperties?.surfacePlacement = .absolute
           graphicsOverlay.sceneProperties?.altitudeOffset = 5
           sceneView.graphicsOverlays.add(graphicsOverlay)
       }
   
       // MARK: Line of Sight Analysis
   
       private let analysisOverlay = AGSAnalysisOverlay()
   
       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)
       }
   
       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)
               }
           }
       }
   
       private func clearObserver() {
           analysisOverlay.analyses.removeAllObjects()
           observerGraphic.geometry = nil
       }
   
       private func addTarget(point: AGSPoint) {
           let targetGraphic = addTargetGraphic(point: point)
           if observerGraphic.geometry != nil {
               createLineOfSightAnalysis(observer: observerGraphic, target: targetGraphic)
           }
       }
   
   }
   
   // MARK: - GeoView Touch Delegate
   
   extension ViewController: AGSGeoViewTouchDelegate {
   
       func geoView(_ geoView: AGSGeoView, didTapAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           addTarget(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {
   
           clearObserver()
   
       }
   
   }
   

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6. 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.

   More info

   • 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.
   ViewController.swift

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   // Copyright 2021 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.
   
   import ArcGIS
   
   class ViewController: UIViewController {
       @IBOutlet weak var sceneView: AGSSceneView!
   
       override func viewDidLoad() {
           super.viewDidLoad()
           setupScene()
   
           setupUI()
   
           setupGraphicsOverlay()
   
           setupAnalysisOverlay()
   
       }
   
       // MARK: Scene
   
       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
   
       }
   
       // MARK: UI
   
       private func setupUI() {
           let clear = UIBarButtonItem(title: "Clear", style: .plain, target: self, action: #selector(clearScene))
           navigationItem.rightBarButtonItem = clear
       }
   
       @objc
       func clearScene(_ sender: UIBarButtonItem) {
           clearAnalyses()
       }
   
       // MARK: Graphics
   
       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)
       }()
   
       @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]
       }
   
       private func setupGraphicsOverlay() {
           graphicsOverlay.graphics.add(observerGraphic)
           graphicsOverlay.sceneProperties?.surfacePlacement = .absolute
           graphicsOverlay.sceneProperties?.altitudeOffset = 5
           sceneView.graphicsOverlays.add(graphicsOverlay)
       }
   
       // MARK: Line of Sight Analysis
   
       private let analysisOverlay = AGSAnalysisOverlay()
   
       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)
       }
   
       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)
               }
           }
       }
   
       private func clearObserver() {
           analysisOverlay.analyses.removeAllObjects()
           observerGraphic.geometry = nil
       }
   
       private func addTarget(point: AGSPoint) {
           let targetGraphic = addTargetGraphic(point: point)
           if observerGraphic.geometry != nil {
               createLineOfSightAnalysis(observer: observerGraphic, target: targetGraphic)
           }
       }
   
   }
   
   // MARK: - GeoView Touch Delegate
   
   extension ViewController: AGSGeoViewTouchDelegate {
   
       func geoView(_ geoView: AGSGeoView, didTapAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           addTarget(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {
   
           clearObserver()
   
       }
   
   }
   

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7. In viewDidLoad(), call the method setupGraphicsOverlay().

   ViewController.swift

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   // Copyright 2021 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.
   
   import ArcGIS
   
   class ViewController: UIViewController {
       @IBOutlet weak var sceneView: AGSSceneView!
   
       override func viewDidLoad() {
           super.viewDidLoad()
           setupScene()
   
           setupUI()
   
           setupGraphicsOverlay()
   
           setupAnalysisOverlay()
   
       }
   
       // MARK: Scene
   
       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
   
       }
   
       // MARK: UI
   
       private func setupUI() {
           let clear = UIBarButtonItem(title: "Clear", style: .plain, target: self, action: #selector(clearScene))
           navigationItem.rightBarButtonItem = clear
       }
   
       @objc
       func clearScene(_ sender: UIBarButtonItem) {
           clearAnalyses()
       }
   
       // MARK: Graphics
   
       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)
       }()
   
       @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]
       }
   
       private func setupGraphicsOverlay() {
           graphicsOverlay.graphics.add(observerGraphic)
           graphicsOverlay.sceneProperties?.surfacePlacement = .absolute
           graphicsOverlay.sceneProperties?.altitudeOffset = 5
           sceneView.graphicsOverlays.add(graphicsOverlay)
       }
   
       // MARK: Line of Sight Analysis
   
       private let analysisOverlay = AGSAnalysisOverlay()
   
       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)
       }
   
       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)
               }
           }
       }
   
       private func clearObserver() {
           analysisOverlay.analyses.removeAllObjects()
           observerGraphic.geometry = nil
       }
   
       private func addTarget(point: AGSPoint) {
           let targetGraphic = addTargetGraphic(point: point)
           if observerGraphic.geometry != nil {
               createLineOfSightAnalysis(observer: observerGraphic, target: targetGraphic)
           }
       }
   
   }
   
   // MARK: - GeoView Touch Delegate
   
   extension ViewController: AGSGeoViewTouchDelegate {
   
       func geoView(_ geoView: AGSGeoView, didTapAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           addTarget(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didMoveLongPressToScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoView(_ geoView: AGSGeoView, didEndLongPressAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
   
           setObserver(point: mapPoint)
   
       }
   
       func geoViewDidCancelLongPress(_ geoView: AGSGeoView) {
   
           clearObserver()
   
       }
   
   }
   

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