Show viewshed from geoelement in scene

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

Image of show viewshed from geoelement in scene sample

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 (a GeoElement). 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 a model (the GeoElement) to represent the observer (in this case, a tank).
    • Use a SimpleRenderer which has a heading expression set in the GraphicsOverlay. This way you can relate the viewshed's heading to the GeoElement object's heading.
  3. Create a GeoElementViewshed with configuration for the viewshed analysis.
  4. Add the viewshed to an AnalysisOverlay and add the overlay to the scene.
  5. Configure the SceneView CameraController to orbit the vehicle.

Relevant API

  • AnalysisOverlay
  • GeodeticDistanceResult
  • GeoElementViewshed
  • ModelSceneSymbol
  • OrbitGeoElementCameraController
  • static GeometryEngine.geodeticDistance(from:to:distanceUnit:azimuthUnit:curveType:)

About the data

This sample shows buildings in Brest, France 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

ShowViewshedFromGeoelementInSceneView.swift
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// Copyright 2023 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 ArcGIS
import SwiftUI

struct ShowViewshedFromGeoelementInSceneView: View {
    /// The view model for the sample.
    @StateObject private var model = Model()

    var body: some View {
        SceneView(
            scene: model.scene,
            cameraController: model.cameraController,
            graphicsOverlays: [model.graphicsOverlay],
            analysisOverlays: [model.analysisOverlay]
        )
        .onSingleTapGesture { _, scenePoint in
            // Move the tank to the scene point on a screen tap.
            guard let scenePoint else { return }
            model.move(toWaypoint: scenePoint)
        }
        .overlay(alignment: .top) {
            // Instruction text.
            Text("Tap on the map to move the tank and update the viewshed.")
                .padding(8)
                .frame(maxWidth: .infinity, alignment: .leading)
                .background(.thinMaterial, ignoresSafeAreaEdges: .horizontal)
        }
        .onDisappear {
            model.stopMoving()
        }
    }
}

private extension ShowViewshedFromGeoelementInSceneView {
    /// The view model for the sample.
    class Model: ObservableObject {
        /// A scene with an imagery basemap.
        let scene: ArcGIS.Scene = {
            let scene = Scene(basemapStyle: .arcGISImagery)

            // Add elevation source to the base surface of the scene with the service URL.
            let elevationSource = ArcGISTiledElevationSource(url: .worldElevationService)
            scene.baseSurface.addElevationSource(elevationSource)

            // Create the building layer and add it to the scene.
            let buildingsLayer = ArcGISSceneLayer(url: .brestBuildingsService)
            scene.addOperationalLayer(buildingsLayer)

            return scene
        }()

        /// A camera controller set to follow the tank.
        let cameraController: CameraController

        /// The graphics overlay for the tank graphic.
        let graphicsOverlay: GraphicsOverlay = {
            let graphicsOverlay = GraphicsOverlay()
            graphicsOverlay.sceneProperties = LayerSceneProperties(surfacePlacement: .relative)

            // Set up the heading expression for the tank.
            let renderer3D = SimpleRenderer()
            let sceneProperties = RendererSceneProperties(
                headingExpression: "[heading]",
                pitchExpression: "[pitch]",
                rollExpression: "[roll]"
            )
            renderer3D.sceneProperties = sceneProperties
            graphicsOverlay.renderer = renderer3D

            return graphicsOverlay
        }()

        /// The analysis overlay for the tank's viewshed.
        let analysisOverlay = AnalysisOverlay()

        /// The graphic for the tank.
        private let tankGraphic: Graphic = {
            let tankSymbol = ModelSceneSymbol(url: .bradleyTank, scale: 10)
            tankSymbol.heading = 90
            tankSymbol.anchorPosition = .bottom
            let tankGraphic = Graphic(
                geometry: Point(latitude: 48.385624, longitude: -4.506390),
                attributes: ["heading": 0.0],
                symbol: tankSymbol
            )
            return tankGraphic
        }()

        /// The point for the tank to move toward.
        private var waypoint: Point? {
            didSet {
                if waypoint == nil {
                    stopMoving()
                }
            }
        }

        /// The timer for the moving tank animation.
        private var animationTimer: Timer?

        init() {
            // Create camera controller.
            cameraController = OrbitGeoElementCameraController(
                target: tankGraphic,
                distance: 200
            )

            // Add tank graphic to graphics overlay.
            graphicsOverlay.addGraphic(tankGraphic)

            // Create a viewshed to attach to the tank.
            let geoElementViewshed = GeoElementViewshed(
                geoElement: tankGraphic,
                horizontalAngle: 90,
                verticalAngle: 40,
                headingOffset: 0,
                pitchOffset: 0,
                minDistance: 0.1,
                maxDistance: 250
            )

            // Offset viewshed observer location to top of tank.
            geoElementViewshed.offsetZ = 3

            // Add the viewshed to the analysisOverlay to add to the scene.
            analysisOverlay.addAnalysis(geoElementViewshed)
        }

        /// Moves the tank to a point.
        /// - Parameter waypoint: The `Point` to move the tank to.
        func move(toWaypoint waypoint: Point) {
            self.waypoint = waypoint

            // Start a timer to animate the tank moving towards the new waypoint.
            animationTimer = Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) { _ in
                self.animate()
            }
        }

        /// Stops moving the tank.
        func stopMoving() {
            animationTimer?.invalidate()
        }

        /// Animates the tank moving from its current point to the waypoint.
        private func animate() {
            // Get point from the current tank position.
            guard let tankLocation = tankGraphic.geometry as? Point,
                  let point = waypoint else { return }

            // Get the distance from the current tank location to the waypoint.
            guard let distanceResult = GeometryEngine.geodeticDistance(
                from: tankLocation,
                to: point,
                distanceUnit: .meters,
                azimuthUnit: .degrees,
                curveType: .geodesic
            ) else { return }

            // Move toward waypoint a short distance.
            let locations = GeometryEngine.geodeticMove(
                [tankLocation],
                distance: 1,
                distanceUnit: .meters,
                azimuth: distanceResult.azimuth1.value,
                azimuthUnit: distanceResult.azimuth1.unit.angularUnit,
                curveType: .geodesic
            )
            tankGraphic.geometry = locations.first

            // Set tank graphic heading.
            if let heading = tankGraphic.attributes["heading"] as? Double {
                // Divide by 10 to make the animation more smooth.
                tankGraphic.setAttributeValue(
                    heading + ((distanceResult.azimuth1.value - heading) / 10),
                    forKey: "heading"
                )
            }

            // Reset waypoint to stop animation when within 5 meters of the waypoint.
            if distanceResult.distance.value <= 5 {
                waypoint = nil
            }
        }
    }
}

private extension URL {
    /// The on-demand resource URL for the Bradley tank.
    static var bradleyTank: URL {
        Bundle.main.url(forResource: "bradle", withExtension: "3ds", subdirectory: "bradley_low_3ds")!
    }

    /// A world elevation service from Terrain3D ArcGIS REST service.
    static var worldElevationService: URL {
        URL(string: "https://elevation3d.arcgis.com/arcgis/rest/services/WorldElevation3D/Terrain3D/ImageServer")!
    }

    /// A scene service URL for buildings in Brest, France.
    static var brestBuildingsService: URL {
        URL(string: "https://tiles.arcgis.com/tiles/P3ePLMYs2RVChkJx/arcgis/rest/services/Buildings_Brest/SceneServer/layers/0")!
    }
}

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