Line of sight (geoelement)

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// Copyright 2022 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.

using ArcGIS.Samples.Managers;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI;
using Esri.ArcGISRuntime.UI.GeoAnalysis;

using Colors = System.Drawing.Color;

namespace ArcGIS.Samples.LineOfSightGeoElement
{
    [ArcGIS.Samples.Shared.Attributes.Sample(
        name: "Line of sight (geoelement)",
        category: "Analysis",
        description: "Show a line of sight between two moving objects.",
        instructions: "A line of sight will display between a point on the Empire State Building (observer) and a taxi (target).",
        tags: new[] { "3D", "line of sight", "visibility", "visibility analysis" })]
    [ArcGIS.Samples.Shared.Attributes.OfflineData("3af5cfec0fd24dac8d88aea679027cb9")]
    public partial class LineOfSightGeoElement : ContentPage
    {
        // URL of the elevation service - provides elevation component of the scene
        private readonly Uri _elevationUri = new Uri("https://elevation3d.arcgis.com/arcgis/rest/services/WorldElevation3D/Terrain3D/ImageServer");

        // URL of the building service - provides builidng models
        private readonly Uri _buildingsUri = new Uri("https://tiles.arcgis.com/tiles/z2tnIkrLQ2BRzr6P/arcgis/rest/services/Buildings_NewYork_v18/SceneServer/layers/0");

        // Starting point of the observation point
        private readonly MapPoint _observerPoint = new MapPoint(-73.984988, 40.748131, 20, SpatialReferences.Wgs84);

        // Graphic to represent the observation point
        private Graphic _observerGraphic;

        // Graphic to represent the observed target
        private Graphic _taxiGraphic;

        // Line of Sight Analysis
        private GeoElementLineOfSight _geoLine;

        // For taxi animation - four points in a loop
        private readonly MapPoint[] _points = {
            new MapPoint(-73.984513, 40.748469, SpatialReferences.Wgs84),
            new MapPoint(-73.985068, 40.747786, SpatialReferences.Wgs84),
            new MapPoint(-73.983452, 40.747091, SpatialReferences.Wgs84),
            new MapPoint(-73.982961, 40.747762, SpatialReferences.Wgs84)
        };

        // For taxi animation - tracks animation state
        private int _pointIndex = 0;
        private int _frameIndex = 0;
        private readonly int _frameMax = 150;

        public LineOfSightGeoElement()
        {
            InitializeComponent();

            // Create the UI, setup the control references and execute initialization
            _ = Initialize();
        }

        private async Task Initialize()
        {
            // Create scene
            Scene myScene = new Scene(BasemapStyle.ArcGISImagery)
            {
                // Set initial viewpoint
                InitialViewpoint = new Viewpoint(_observerPoint, 1600)
            };
            // Create the elevation source
            ElevationSource myElevationSource = new ArcGISTiledElevationSource(_elevationUri);
            // Add the elevation source to the scene
            myScene.BaseSurface.ElevationSources.Add(myElevationSource);
            // Create the building scene layer
            ArcGISSceneLayer mySceneLayer = new ArcGISSceneLayer(_buildingsUri);
            // Add the building layer to the scene
            myScene.OperationalLayers.Add(mySceneLayer);

            // Add the observer to the scene
            // Create a graphics overlay with relative surface placement; relative surface placement allows the Z position of the observation point to be adjusted
            GraphicsOverlay overlay = new GraphicsOverlay() { SceneProperties = new LayerSceneProperties(SurfacePlacement.Relative) };
            // Create the symbol that will symbolize the observation point
            SimpleMarkerSceneSymbol symbol = new SimpleMarkerSceneSymbol(SimpleMarkerSceneSymbolStyle.Sphere, Colors.Red, 10, 10, 10, SceneSymbolAnchorPosition.Bottom);
            // Create the observation point graphic from the point and symbol
            _observerGraphic = new Graphic(_observerPoint, symbol);
            // Add the observer to the overlay
            overlay.Graphics.Add(_observerGraphic);
            // Add the overlay to the scene
            MySceneView.GraphicsOverlays.Add(overlay);

            try
            {
                // Add the taxi to the scene
                // Create the model symbol for the taxi
                ModelSceneSymbol taxiSymbol = await ModelSceneSymbol.CreateAsync(new Uri(GetModelUri()));
                // Set the anchor position for the mode; ensures that the model appears above the ground
                taxiSymbol.AnchorPosition = SceneSymbolAnchorPosition.Bottom;
                // Create the graphic from the taxi starting point and the symbol
                _taxiGraphic = new Graphic(_points[0], taxiSymbol);
                // Add the taxi graphic to the overlay
                overlay.Graphics.Add(_taxiGraphic);

                // Create GeoElement Line of sight analysis (taxi to building)
                // Create the analysis
                _geoLine = new GeoElementLineOfSight(_observerGraphic, _taxiGraphic)
                {
                    // Apply an offset to the target. This helps avoid some false negatives
                    TargetOffsetZ = 2
                };
                // Create the analysis overlay
                AnalysisOverlay myAnalysisOverlay = new AnalysisOverlay();
                // Add the analysis to the overlay
                myAnalysisOverlay.Analyses.Add(_geoLine);
                // Add the analysis overlay to the scene
                MySceneView.AnalysisOverlays.Add(myAnalysisOverlay);

                // Create a timer; this will enable animating the taxi
                Dispatcher.StartTimer(new TimeSpan(0, 0, 0, 0, 60), () =>
                {
                    // Move the taxi every time the timer elapses
                    AnimationTimer_Elapsed(this, null);
                    // Keep the timer running
                    return true;
                });

                // Subscribe to TargetVisible events; allows for updating the UI and selecting the taxi when it is visible
                _geoLine.TargetVisibilityChanged += Geoline_TargetVisibilityChanged;

                // Add the scene to the view
                MySceneView.Scene = myScene;
            }
            catch (Exception e)
            {
                await Application.Current.MainPage.DisplayAlert("Error", e.ToString(), "OK");
            }
        }

        private void AnimationTimer_Elapsed(object sender, EventArgs e)
        {
            // Note: the contents of this function are solely related to animating the taxi

            // Increment the frame counter
            _frameIndex++;

            // Reset the frame counter once one segment of the path has been travelled
            if (_frameIndex == _frameMax)
            {
                _frameIndex = 0;

                // Start navigating toward the next point
                _pointIndex++;

                // Restart if finished circuit
                if (_pointIndex == _points.Length)
                {
                    _pointIndex = 0;
                }
            }

            // Get the point the taxi is travelling from
            MapPoint starting = _points[_pointIndex];
            // Get the point the taxi is travelling to
            MapPoint ending = _points[(_pointIndex + 1) % _points.Length];
            // Calculate the progress based on the current frame
            double progress = _frameIndex / (double)_frameMax;
            // Calculate the position of the taxi when it is {progress}% of the way through
            MapPoint intermediatePoint = InterpolatedPoint(starting, ending, progress);
            // Update the taxi geometry
            _taxiGraphic.Geometry = intermediatePoint;

            // Update the taxi rotation.
            GeodeticDistanceResult distance = starting.DistanceGeodetic(ending, LinearUnits.Meters, AngularUnits.Degrees, GeodeticCurveType.Geodesic);
            ((ModelSceneSymbol)_taxiGraphic.Symbol).Heading = distance.Azimuth1;
        }

        private MapPoint InterpolatedPoint(MapPoint firstPoint, MapPoint secondPoint, double progress)
        {
            // This function returns a MapPoint that is the result of travelling {progress}% of the way from {firstPoint} to {secondPoint}

            // Get the difference between the two points
            MapPoint difference = new MapPoint(secondPoint.X - firstPoint.X, secondPoint.Y - firstPoint.Y, secondPoint.Z - firstPoint.Z, SpatialReferences.Wgs84);
            // Scale the difference by the progress towards the destination
            MapPoint scaled = new MapPoint(difference.X * progress, difference.Y * progress, difference.Z * progress);
            // Add the scaled progress to the starting point
            return new MapPoint(firstPoint.X + scaled.X, firstPoint.Y + scaled.Y, firstPoint.Z + scaled.Z);
        }

        private void Geoline_TargetVisibilityChanged(object sender, EventArgs e)
        {
            // This is needed because Runtime delivers notifications from a different thread that doesn't have access to UI controls
            Microsoft.Maui.ApplicationModel.MainThread.BeginInvokeOnMainThread(UpdateUiAndSelection);
        }

        private void UpdateUiAndSelection()
        {
            switch (_geoLine.TargetVisibility)
            {
                case LineOfSightTargetVisibility.Obstructed:
                    MyStatusLabel.Text = "Status: Obstructed";
                    _taxiGraphic.IsSelected = false;
                    break;

                case LineOfSightTargetVisibility.Visible:
                    MyStatusLabel.Text = "Status: Visible";
                    _taxiGraphic.IsSelected = true;
                    break;

                default:
                case LineOfSightTargetVisibility.Unknown:
                    MyStatusLabel.Text = "Status: Unknown";
                    _taxiGraphic.IsSelected = false;
                    break;
            }
        }

        private static string GetModelUri()
        {
            // Returns the taxi model

            return DataManager.GetDataFolder("3af5cfec0fd24dac8d88aea679027cb9", "dolmus.3ds");
        }

        private void MyHeightSlider_ValueChanged(object sender, EventArgs e)
        {
            // Update the height of the observer based on the slider value

            // Constrain the min and max to 20 and 150 units
            double minHeight = 20;
            double maxHeight = 150;

            // Scale the slider value; its default range is 0-10
            double value = MyHeightSlider.Value;

            // Get the current point
            MapPoint oldPoint = (MapPoint)_observerGraphic.Geometry;

            // Create a new point with the same (x,y) but updated z
            MapPoint newPoint = new MapPoint(oldPoint.X, oldPoint.Y, (maxHeight - minHeight) * value + minHeight);

            // Apply the updated geometry to the observer point
            _observerGraphic.Geometry = newPoint;
        }
    }
}