List KML contents

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List the contents of a KML file.

Image of list KML contents

Use case

KML files can contain a hierarchy of features, including network links to other KML content. A user may wish to traverse through the contents of KML nodes to know what data is contained within each node and, recursively, their children.

How to use the sample

The contents of the KML file are shown in a tree. Select a node to zoom to that node. Not all nodes can be zoomed to (e.g. screen overlays).

How it works

  1. Add the KML file to the scene as a layer.
  2. Explore the root nodes of the KmlDataset recursively explored to create a view model.
  3. Each node is enabled for display at this step. KML files may include nodes that are turned off by default.
  4. When a node is selected, use the node's Extent to determine a viewpoint and set the SceneView object's viewpoint do it.

Relevant API

  • KmlContainer
  • KmlDataset
  • KmlDocument
  • KmlFolder
  • KmlGroundOverlay
  • KmlLayer
  • KmlNetworkLink
  • KmlNode
  • KmlPlacemark
  • KmlScreenOverlay

About the data

This is an example KML file meant to demonstrate how Runtime supports several common features.

Tags

Keyhole, KML, KMZ, layers, OGC

Sample Code

ListKmlContents.cs
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
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// Copyright 2018 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 ArcGISRuntime;
using ArcGISRuntime.Samples.Managers;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Ogc;
using Esri.ArcGISRuntime.UI.Controls;
using Foundation;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using UIKit;

namespace ArcGISRuntimeXamarin.Samples.ListKmlContents
{
    [Register("ListKmlContents")]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "List KML contents",
        category: "Layers",
        description: "List the contents of a KML file.",
        instructions: "The contents of the KML file are shown in a tree. Select a node to zoom to that node. Not all nodes can be zoomed to (e.g. screen overlays).",
        tags: new[] { "KML", "KMZ", "Keyhole", "OGC", "layers" })]
    [ArcGISRuntime.Samples.Shared.Attributes.OfflineData("da301cb122874d5497f8a8f6c81eb36e")]
    public class ListKmlContents : UIViewController
    {
        // Hold references to UI controls.
        private SceneView _mySceneView;
        private UITableView _myDisplayList;
        private LayerListSource _layerListSource;
        private UIStackView _stackView;

        // Hold a list of LayerDisplayVM; this is the ViewModel.
        private readonly List<LayerDisplayVM> _viewModelList = new List<LayerDisplayVM>();

        public ListKmlContents()
        {
            Title = "List KML contents";
        }

        private async void Initialize()
        {
            // Add a basemap.
            _mySceneView.Scene = new Scene(Basemap.CreateImageryWithLabels());
            _mySceneView.Scene.BaseSurface.ElevationSources.Add(new ArcGISTiledElevationSource(new Uri("https://elevation3d.arcgis.com/arcgis/rest/services/WorldElevation3D/Terrain3D/ImageServer")));

            // Get the URL to the data.
            Uri kmlUrl = new Uri(DataManager.GetDataFolder("da301cb122874d5497f8a8f6c81eb36e", "esri_test_data.kmz"));

            // Create the KML dataset and layer.
            KmlDataset dataset = new KmlDataset(kmlUrl);
            KmlLayer layer = new KmlLayer(dataset);

            // Add the layer to the map.
            _mySceneView.Scene.OperationalLayers.Add(layer);

            try
            {
                await dataset.LoadAsync();

                // Build the ViewModel from the expanded list of layer infos.
                foreach (KmlNode node in dataset.RootNodes)
                {
                    // LayerDisplayVM is a custom type made for this sample to serve as the ViewModel; it is not a part of ArcGIS Runtime.
                    LayerDisplayVM nodeVm = new LayerDisplayVM(node, null);
                    _viewModelList.Add(nodeVm);
                    LayerDisplayVM.BuildLayerInfoList(nodeVm, _viewModelList);
                }

                // Construct the layer list source.
                _layerListSource = new LayerListSource(_viewModelList, this);

                // Set the source for the table view (layer list).
                _myDisplayList.Source = _layerListSource;

                // Force an update of the list display.
                _myDisplayList.ReloadData();
            }
            catch (Exception e)
            {
                new UIAlertView("Error", e.ToString(), (IUIAlertViewDelegate) null, "OK", null).Show();
            }
        }


        /// <summary>
        /// Takes action once a new content selection is made.
        /// </summary>
        public void ContentSelectionChanged(int selectedIndex)
        {
            // Get the KML node.
            LayerDisplayVM selectedItem = _viewModelList[selectedIndex];

            NavigateToNode(selectedItem.Node);
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();
            Initialize();
        }

        public override void LoadView()
        {
            // Create the views.
            View = new UIView() { BackgroundColor = ApplicationTheme.BackgroundColor };

            _mySceneView = new SceneView();
            _mySceneView.TranslatesAutoresizingMaskIntoConstraints = false;

            _myDisplayList = new UITableView
            {
                RowHeight = 30
            };
            _myDisplayList.TranslatesAutoresizingMaskIntoConstraints = false;

            _stackView = new UIStackView(new UIView[] {_mySceneView, _myDisplayList});
            _stackView.TranslatesAutoresizingMaskIntoConstraints = false;
            _stackView.Axis = UILayoutConstraintAxis.Vertical;
            _stackView.Distribution = UIStackViewDistribution.FillEqually;

            // Add the views.
            View.AddSubviews(_stackView);

            // Lay out the views.
            NSLayoutConstraint.ActivateConstraints(new[]
            {
                _stackView.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                _stackView.BottomAnchor.ConstraintEqualTo(View.BottomAnchor),
                _stackView.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _stackView.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor)
            });
        }

        public override void TraitCollectionDidChange(UITraitCollection previousTraitCollection)
        {
            base.TraitCollectionDidChange(previousTraitCollection);
            if (View.TraitCollection.VerticalSizeClass == UIUserInterfaceSizeClass.Compact)
            {
                _stackView.Axis = UILayoutConstraintAxis.Horizontal;
            }
            else
            {
                _stackView.Axis = UILayoutConstraintAxis.Vertical;
            }
        }

        #region viewpoint_conversion

        private async void NavigateToNode(KmlNode node)
        {
            try
            {
                // Get a corrected Runtime viewpoint using the KmlViewpoint.
                bool viewpointNeedsAltitudeAdjustment;
                Viewpoint runtimeViewpoint = ViewpointFromKmlViewpoint(node, out viewpointNeedsAltitudeAdjustment);
                if (viewpointNeedsAltitudeAdjustment)
                {
                    runtimeViewpoint = await GetAltitudeAdjustedViewpointAsync(node, runtimeViewpoint);
                }

                // Set the viewpoint.
                if (runtimeViewpoint != null && !runtimeViewpoint.TargetGeometry.IsEmpty)
                {
                    await _mySceneView.SetViewpointAsync(runtimeViewpoint);
                }
            }
            catch (Exception e)
            {
                new UIAlertView("Error", e.ToString(), (IUIAlertViewDelegate) null, "OK", null).Show();
            }
        }

        private Viewpoint ViewpointFromKmlViewpoint(KmlNode node, out bool needsAltitudeFix)
        {
            KmlViewpoint kvp = node.Viewpoint;
            // If KmlViewpoint is specified, use it.
            if (kvp != null)
            {
                // Altitude adjustment is needed for everything except Absolute altitude mode.
                needsAltitudeFix = (kvp.AltitudeMode != KmlAltitudeMode.Absolute);
                switch (kvp.Type)
                {
                    case KmlViewpointType.LookAt:
                        return new Viewpoint(kvp.Location,
                            new Camera(kvp.Location, kvp.Range, kvp.Heading, kvp.Pitch, kvp.Roll));
                    case KmlViewpointType.Camera:
                        return new Viewpoint(kvp.Location,
                            new Camera(kvp.Location, kvp.Heading, kvp.Pitch, kvp.Roll));
                    default:
                        throw new InvalidOperationException("Unexpected KmlViewPointType: " + kvp.Type);
                }
            }

            if (node.Extent != null && !node.Extent.IsEmpty)
            {
                // When no altitude specified, assume elevation should be taken into account.
                needsAltitudeFix = true;

                // Workaround: it's possible for "IsEmpty" to be true but for width/height to still be zero.
                if (node.Extent.Width == 0 && node.Extent.Height == 0)
                {
                    // Defaults based on Google Earth.
                    return new Viewpoint(node.Extent, new Camera(node.Extent.GetCenter(), 1000, 0, 45, 0));
                }

                Envelope tx = node.Extent;
                // Add padding on each side.
                double bufferDistance = Math.Max(node.Extent.Width, node.Extent.Height) / 20;
                Envelope bufferedExtent = new Envelope(
                    tx.XMin - bufferDistance, tx.YMin - bufferDistance,
                    tx.XMax + bufferDistance, tx.YMax + bufferDistance,
                    tx.ZMin - bufferDistance, tx.ZMax + bufferDistance,
                    SpatialReferences.Wgs84);
                return new Viewpoint(bufferedExtent);
            }
            else
            {
                // Can't fly to.
                needsAltitudeFix = false;
                return null;
            }
        }

        // Asynchronously adjust the given viewpoint, taking into consideration elevation and KML altitude mode.
        private async Task<Viewpoint> GetAltitudeAdjustedViewpointAsync(KmlNode node, Viewpoint baseViewpoint)
        {
            // Get the altitude mode; assume clamp-to-ground if not specified.
            KmlAltitudeMode altMode = KmlAltitudeMode.ClampToGround;
            if (node.Viewpoint != null)
            {
                altMode = node.Viewpoint.AltitudeMode;
            }

            // If the altitude mode is Absolute, the base viewpoint doesn't need adjustment.
            if (altMode == KmlAltitudeMode.Absolute)
            {
                return baseViewpoint;
            }

            double altitude;
            Envelope lookAtExtent = baseViewpoint.TargetGeometry as Envelope;
            MapPoint lookAtPoint = baseViewpoint.TargetGeometry as MapPoint;

            if (lookAtExtent != null)
            {
                // Get the altitude for the extent.
                try
                {
                    altitude = await _mySceneView.Scene.BaseSurface.GetElevationAsync(lookAtExtent.GetCenter());
                }
                catch (Exception)
                {
                    altitude = 0;
                }

                // Apply elevation adjustment to the geometry.
                Envelope target;
                if (altMode == KmlAltitudeMode.ClampToGround)
                {
                    target = new Envelope(
                        lookAtExtent.XMin, lookAtExtent.YMin,
                        lookAtExtent.XMax, lookAtExtent.YMax,
                        altitude, lookAtExtent.Depth + altitude,
                        lookAtExtent.SpatialReference);
                }
                else
                {
                    target = new Envelope(
                        lookAtExtent.XMin, lookAtExtent.YMin,
                        lookAtExtent.XMax, lookAtExtent.YMax,
                        lookAtExtent.ZMin + altitude, lookAtExtent.ZMax + altitude,
                        lookAtExtent.SpatialReference);
                }

                if (node.Viewpoint != null)
                {
                    // Return adjusted geometry with adjusted camera if a viewpoint was specified on the node.
                    return new Viewpoint(target, baseViewpoint.Camera.Elevate(altitude));
                }
                else
                {
                    // Return adjusted geometry.
                    return new Viewpoint(target);
                }
            }
            else if (lookAtPoint != null)
            {
                // Get the altitude adjustment.
                try
                {
                    altitude = await _mySceneView.Scene.BaseSurface.GetElevationAsync(lookAtPoint);
                }
                catch (Exception)
                {
                    altitude = 0;
                }

                // Apply elevation adjustment to the geometry.
                MapPoint target;
                if (altMode == KmlAltitudeMode.ClampToGround)
                {
                    target = new MapPoint(lookAtPoint.X, lookAtPoint.Y, altitude, lookAtPoint.SpatialReference);
                }
                else
                {
                    target = new MapPoint(
                        lookAtPoint.X, lookAtPoint.Y, lookAtPoint.Z + altitude,
                        lookAtPoint.SpatialReference);
                }

                if (node.Viewpoint != null)
                {
                    // Return adjusted geometry with adjusted camera if a viewpoint was specified on the node.
                    return new Viewpoint(target, baseViewpoint.Camera.Elevate(altitude));
                }
                else
                {
                    // Google Earth defaults: 1000m away and 45-degree tilt.
                    return new Viewpoint(target, new Camera(target, 1000, 0, 45, 0));
                }
            }
            else
            {
                throw new InvalidOperationException("KmlNode has unexpected Geometry for its Extent: " +
                                                    baseViewpoint.TargetGeometry);
            }
        }

        #endregion viewpoint_conversion
    }

    public class LayerDisplayVM
    {
        public KmlNode Node { get; }

        private LayerDisplayVM Parent { get; set; }

        private int NestLevel
        {
            get
            {
                if (Parent == null)
                {
                    return 0;
                }

                return Parent.NestLevel + 1;
            }
        }

        public LayerDisplayVM(KmlNode info, LayerDisplayVM parent)
        {
            Node = info;
            Parent = parent;
        }

        public string Name => new string(' ', NestLevel * 3) + Node.GetType().Name + " - " + Node.Name;

        public static void BuildLayerInfoList(LayerDisplayVM root, IList<LayerDisplayVM> result)
        {
            // Add the root node to the result list.
            result.Add(root);

            // Make the node visible.
            root.Node.IsVisible = true;

            // Recursively add children. KmlContainers and KmlNetworkLinks can both have children.
            var containerNode = root.Node as KmlContainer;
            var networkLinkNode = root.Node as KmlNetworkLink;

            List<KmlNode> children = new List<KmlNode>();
            if (containerNode != null)
            {
                children.AddRange(containerNode.ChildNodes);
            }

            if (networkLinkNode != null)
            {
                children.AddRange(networkLinkNode.ChildNodes);
            }

            foreach (KmlNode node in children)
            {
                // Create the view model for the sublayer.
                LayerDisplayVM layerVm = new LayerDisplayVM(node, root);

                // Recursively add children.
                BuildLayerInfoList(layerVm, result);
            }
        }
    }

    /// <summary>
    /// Class defines how a UITableView renders its contents.
    /// This implements the list of KML content.
    /// </summary>
    public class LayerListSource : UITableViewSource
    {
        private readonly List<LayerDisplayVM> ViewModelList = new List<LayerDisplayVM>();

        // Used when re-using cells to ensure that a cell of the right type is used
        private const string CellId = "KmlContentCell";

        // Hold a reference to the owning view controller; this will be the active instance of ListKmlContents.
        [Weak] public ListKmlContents Owner;

        public LayerListSource(List<LayerDisplayVM> items, ListKmlContents owner)
        {
            // Set the items.
            if (items != null)
            {
                ViewModelList = items;
            }

            // Set the owner.
            Owner = owner;
        }

        /// <summary>
        /// This method gets a table view cell for the suggestion at the specified index.
        /// </summary>
        public override UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath)
        {
            // Try to get a re-usable cell (this is for performance).
            UITableViewCell cell = tableView.DequeueReusableCell(CellId);

            // If there are no cells, create a new one.
            if (cell == null)
            {
                cell = new UITableViewCell(UITableViewCellStyle.Default, CellId)
                {
                    BackgroundColor = UIColor.FromWhiteAlpha(0, 0f)
                };
                cell.TextLabel.TextColor = Owner.View.TintColor;
            }

            // Get the specific item to display.
            LayerDisplayVM item = ViewModelList[indexPath.Row];

            // Set the text on the cell.
            cell.TextLabel.Text = item.Name;

            // Return the cell.
            return cell;
        }

        /// <summary>
        /// This method allows the UITableView to know how many rows to render.
        /// </summary>
        public override nint RowsInSection(UITableView tableview, nint section)
        {
            return ViewModelList.Count;
        }

        /// <summary>
        /// Method called when a row is selected; notifies the primary view.
        /// </summary>
        public override void RowSelected(UITableView tableView, NSIndexPath indexPath)
        {
            // Deselect the row.
            tableView.DeselectRow(indexPath, true);

            // Select the content.
            Owner.ContentSelectionChanged(indexPath.Row);
        }
    }
}

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