Viewshed (GeoElement)

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Analyze the viewshed for an object (geo element) in a scene.

Viewshed (GeoElement)

Use case

A viewshed analysis is a type of visual analysis you can perform on a scene. The viewshed aims to answer the question 'What can I see from a given location?'. The output is an overlay with two different colors - one representing the visible areas (green) and the other representing the obstructed areas (red).

How to use the sample

Tap to set a destination for the vehicle (an AGSGeoElement). The vehicle will 'drive' towards the tapped location. The viewshed analysis will update as the vehicle moves.

How it works

  1. Create and show the scene, with an elevation source and a buildings layer.
  2. Add an AGSModelSceneSymbol (the GeoElement) to represent the observer (in this case, a tank).

    • Use an AGSSimpleRenderer which has a heading expression set in the AGSRendererSceneProperties. This way you can relate the viewshed's heading to the object's heading.
  3. Create an AGSGeoElementViewshed with configuration for the viewshed analysis.
  4. Add the viewshed to an AGSAnalysisOverlay and add the overlay to the scene.
  5. Configure the SceneView AGSCameraController to orbit the vehicle.

Relevant API

  • AGSAnalysisOverlay
  • AGSGeodeticDistanceResult
  • AGSGeoElementViewshed
  • AGSGeometryEngine
  • AGSModelSceneSymbol
  • AGSOrbitGeoElementCameraController

Offline data

Model Marker Symbol Data will be downloaded by the sample viewer automatically.

About the data

This sample shows a Johannesburg, South Africa Scene from ArcGIS Online. The sample uses a Tank model scene symbol hosted as an item on ArcGIS Online.

Tags

3D, analysis, buildings, model, scene, viewshed, visibility analysis

Sample Code

ViewshedGeoElementViewController.swift
                                                                                                                                                                   
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// Copyright 2017 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 UIKit
import ArcGIS

class ViewshedGeoElementViewController: UIViewController, AGSGeoViewTouchDelegate {
    @IBOutlet var sceneView: AGSSceneView!
    var tank = AGSGraphic()
    var waypoint: AGSPoint?
    var animationTimer: Timer?

    override func viewDidLoad() {
        super.viewDidLoad()

        // Add the source code button item to the right of navigation bar
        (navigationItem.rightBarButtonItem as! SourceCodeBarButtonItem).filenames = ["ViewshedGeoElementViewController"]

        // set the sceneView's touch delegate so we can get user taps
        sceneView.touchDelegate = self

        let graphicsOverlay = makeGraphicsOverlay()
        sceneView.graphicsOverlays.add(graphicsOverlay)

        let analysisOverlay = makeAnalysisOverlay()
        sceneView.analysisOverlays.add(analysisOverlay)

        let cameraController = makeCameraController()
        sceneView.cameraController = cameraController

        sceneView.scene = makeScene()
    }

    private func makeScene() -> AGSScene {
        // create the scene
        let scene = AGSScene(basemap: .imagery())

        // add base surface for elevation data
        let surface = AGSSurface()
        /// The url of the image service for elevation in Brest, France.
        let brestElevationServiceURL = URL(string: "https://scene.arcgis.com/arcgis/rest/services/BREST_DTM_1M/ImageServer")!
        let elevationSource = AGSArcGISTiledElevationSource(url: brestElevationServiceURL)
        surface.elevationSources.append(elevationSource)
        scene.baseSurface = surface

        /// The url of the scene service for buildings in Brest, France.
        let brestBuildingsServiceURL = URL(string: "https://tiles.arcgis.com/tiles/P3ePLMYs2RVChkJx/arcgis/rest/services/Buildings_Brest/SceneServer/layers/0")!
        // add a scene layer
        let buildings = AGSArcGISSceneLayer(url: brestBuildingsServiceURL)
        scene.operationalLayers.add(buildings)

        return scene
    }

    private func makeGraphicsOverlay() -> AGSGraphicsOverlay {
        // create a graphics overlay for the tank
        let graphicsOverlay = AGSGraphicsOverlay()
        graphicsOverlay.sceneProperties = AGSLayerSceneProperties(surfacePlacement: .relative)

        // set up heading expression for tank
        let renderer3D = AGSSimpleRenderer()
        let sceneProperties = AGSRendererSceneProperties(headingExpression: "[heading] + 90", pitchExpression: "[pitch]", rollExpression: "[roll]")
        sceneProperties.headingExpression = "[HEADING]"
        renderer3D.sceneProperties = sceneProperties
        graphicsOverlay.renderer = renderer3D

        // create a graphic of a tank
        let tankSymbol = AGSModelSceneSymbol(name: "bradle", extension: "3ds", scale: 10.0)
        tankSymbol.heading = 90.0
        tankSymbol.anchorPosition = .bottom
        tank = AGSGraphic(
            geometry: AGSPoint(x: -4.506390,
                               y: 48.385624,
                               spatialReference: .wgs84()),
            symbol: tankSymbol,
            attributes: ["HEADING": 0.0]
        )
        graphicsOverlay.graphics.add(tank)
        return graphicsOverlay
    }

    private func makeAnalysisOverlay() -> AGSAnalysisOverlay {
        // create a viewshed to attach to the tank
        let geoElementViewshed = AGSGeoElementViewshed(
           geoElement: tank,
           horizontalAngle: 90.0,
           verticalAngle: 40.0,
           minDistance: 0.1,
           maxDistance: 250.0,
           headingOffset: 0.0,
           pitchOffset: 0.0
        )

        // offset viewshed observer location to top of tank
        geoElementViewshed.offsetZ = 3.0

        // create an analysis overlay to add the viewshed to the scene view
        let analysisOverlay = AGSAnalysisOverlay()
        analysisOverlay.analyses.add(geoElementViewshed)
        return analysisOverlay
    }

    private func makeCameraController() -> AGSCameraController {
        // set camera controller to follow tank
        let cameraController = AGSOrbitGeoElementCameraController(targetGeoElement: tank, distance: 200.0)
        cameraController.cameraPitchOffset = 45.0
        return cameraController
    }

    func geoView(_ geoView: AGSGeoView, didTapAtScreenPoint screenPoint: CGPoint, mapPoint: AGSPoint) {
        // set the new waypoint
        waypoint = mapPoint

        // start a timer to animate towards the waypoint
        animationTimer = Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) { [weak self] _ in
            self?.animate()
        }
    }

    private func animate() {
        guard let waypoint = waypoint,
            let location = tank.geometry as? AGSPoint else { return }

        guard let distanceResult = AGSGeometryEngine.geodeticDistanceBetweenPoint1(location,
                                                                                   point2: waypoint,
                                                                                   distanceUnit: AGSLinearUnit.meters(),
                                                                                   azimuthUnit: AGSAngularUnit.degrees(),
                                                                                   curveType: .geodesic) else { return }

        // move toward waypoint a short distance
        let locations = AGSGeometryEngine.geodeticMove([location],
                                                       distance: 1.0,
                                                       distanceUnit: AGSLinearUnit.meters(),
                                                       azimuth: distanceResult.azimuth1,
                                                       azimuthUnit: distanceResult.azimuthUnit ?? AGSAngularUnit.degrees(),
                                                       curveType: .geodesic)

        if let newLocation = locations?.first {
            tank.geometry = newLocation
        }

        if let heading = tank.attributes["HEADING"] as? Double {
            tank.attributes["HEADING"] = heading + ((distanceResult.azimuth1 - heading) / 10)
        }

        // stop the animation when we're within 5 meters of the waypoint
        if distanceResult.distance <= 5 {
            self.waypoint = nil
            animationTimer?.invalidate()
        }
    }
}

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