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 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.
More info 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 APIKeyAGSArcGISRuntime 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
}
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 setup method to create an AGSSceneitem ID and an AGSPortal
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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
}
Add a UI to control the viewshed analysis To control the viewshed analysis, some UI elements are required.
Create a private UISliderslider. The slider changes the viewshed's maximum distance by expanding or contracting the size of the observer's field of view. The maximum and minimum 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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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
}()
Define a private method named setup and assign the slider as well as a "Clear" button to the navigation bar. The clear button removes the viewshed from the sceneYou 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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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
}()
private func setupUI () {
navigationItem.titleView = slider
navigationItem.rightBarButtonItem = UIBarButtonItem (
title: "Clear" ,
style: .plain,
target: self ,
action: #selector(clearScene)
)
}
Define a method named slider and assign it the @objc keyword. This method updates the viewshed's max 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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private func setupUI () {
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)
}
Define a method named clear 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 UIBar API.
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@objc
func sliderValueDidChange ( _ sender : UISlider ) {
viewshed.maxDistance = Double (sender.value)
}
@objc
func clearScene ( _ sender : UIBarButtonItem ) {
clearViewshed()
}
In view, call the method setup.
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override func viewDidLoad () {
super .viewDidLoad()
setupScene()
setupUI()
}
In Xcode , in the Project Navigator , click Main.storyboard .
In the editor , select View. In the menu bar , click Editor > Embed In > Navigation Controller .
More info Embedding View within a Navigation Controller places a navigation bar at the top of View. 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 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. Upon launch, the viewshed should not be visible.
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private lazy var viewshed: AGSLocationViewshed = {
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
}()
Define a private method named setup to add the viewshed to the scene.
More info The viewshed analysis is added to a scene view using an analysis overlay. An analysis overlay is a container for analyses. It can be used to display visual analyses in a scene view. You can add more than one analysis overlay and they are displayed on top of all other layers .
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private lazy var viewshed: AGSLocationViewshed = {
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)
}
Define a private method named set 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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private func setupAnalysisOverlay () {
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
}
}
Define a private method named clear. This method is used to hide the viewshed.
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private func setViewshedLocation ( point : AGSPoint ) {
viewshed.location = point
if ! viewshed.isVisible {
viewshed.isVisible = true
}
}
private func clearViewshed () {
viewshed.isVisible = false
}
In view, call setup.
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override func viewDidLoad () {
super .viewDidLoad()
setupScene()
setupUI()
setupAnalysisOverlay()
}
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 View to conform to the AGSGeogeoview touch delegate methods.
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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 set. 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.
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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 clear.
More info 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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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 setup method, assign View to scene.
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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
sceneView.touchDelegate = self
}
Run the app Press <Command+R> to run the app.
More info 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:
