Browse OGC API feature service

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Browse an OGC API feature service for layers and add them to the map.

Image of browse OGC API feature service

Use case

OGC API standards are used for sharing geospatial data on the web. As an open standard, the OGC API aims to improve access to geospatial or location information and could be a good choice for sharing data internationally or between organizations. That data could be of any type, including, for example transportation layers shared between government organizations and private businesses.

How to use the sample

Select a layer to display from the list of layers shown in an OGC API service.

How it works

  1. Create an OgcFeatureService object with a URL to an OGC API feature service.
  2. Obtain the OgcFeatureServiceInfo from OgcFeatureService.ServiceInfo.
  3. Create a list of feature collections from the OgcFeatureServiceInfo.FeatureCollectionInfos
  4. When a feature collection is selected, create an OgcFeatureCollectionTable from the OgcFeatureCollectionInfo.
  5. Populate the OgcFeatureCollectionTable using PopulateFromServiceAsync with QueryParameters that contain a MaxFeatures property.
  6. Create a feature layer from the feature table.
  7. Add the feature layer to the map.

Relevant API

  • OgcFeatureCollectionInfo
  • OgcFeatureCollectionTable
  • OgcFeatureService
  • OgcFeatureServiceInfo

About the data

The Daraa, Syria test data is OpenStreetMap data converted to the Topographic Data Store schema of NGA.

Additional information

See the OGC API website for more information on the OGC API family of standards.

Tags

browse, catalog, feature, layers, OGC, OGC API, service, web

Sample Code

BrowseOAFeatureService.cs
                                                                                                                                                                                                                                                                                     
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// Copyright 2021 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 Esri.ArcGISRuntime.Data;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Ogc;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI.Controls;
using Foundation;
using System;
using System.Diagnostics;
using System.Drawing;
using UIKit;

namespace ArcGISRuntimeXamarin.Samples.BrowseOAFeatureService
{
    [Register("BrowseOAFeatureService")]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Browse OGC API feature service",
        category: "Layers",
        description: "Browse an OGC API feature service for layers and add them to the map.",
        instructions: "Select a layer to display from the list of layers shown in an OGC API service.",
        tags: new[] { "OGC", "OGC API", "browse", "catalog", "feature", "layers", "service", "web" })]
    public class BrowseOAFeatureService : UIViewController
    {
        // Hold references to UI controls.
        private MapView _myMapView;
        private UIActivityIndicatorView _loadingProgressBar;
        private UIBarButtonItem _chooseLayersButton;
        private UIBarButtonItem _loadServiceButton;

        // Hold a reference to the service info.
        private OgcFeatureServiceInfo _serviceInfo;

        // URL for the OGC feature service.
        private const string _serviceUrl = "https://demo.ldproxy.net/daraa";

        public BrowseOAFeatureService()
        {
            Title = "Browse OGC API feature service";
        }

        private void Initialize()
        {
            // Create the map with topographic basemap.
            _myMapView.Map = new Map(BasemapStyle.ArcGISTopographic);

            LoadService(_serviceUrl);
        }

        private async void LoadService(string serviceUrl)
        {
            try
            {
                _loadingProgressBar.StartAnimating();
                _loadServiceButton.Enabled = false;
                _chooseLayersButton.Enabled = false;

                // Create the OGC API - Features service using the landing URL.
                OgcFeatureService service = new OgcFeatureService(new Uri(serviceUrl));

                // Load the service.
                await service.LoadAsync();

                // Get the service metadata.
                _serviceInfo = service.ServiceInfo;
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex);
                new UIAlertView("Error loading service", ex.Message, (IUIAlertViewDelegate)null, "OK", null).Show();
            }
            finally
            {
                // Update the UI.
                _loadingProgressBar.StopAnimating();
                _loadServiceButton.Enabled = true;
                _chooseLayersButton.Enabled = true;
            }
        }

        private async void LoadSelectedLayer(OgcFeatureCollectionInfo selectedLayerInfo)
        {
            // Show the progress bar.
            _loadingProgressBar.StartAnimating();

            // Clear the existing layers.
            _myMapView.Map.OperationalLayers.Clear();

            try
            {
                // Create the OGC feature collection table.
                OgcFeatureCollectionTable table = new OgcFeatureCollectionTable(selectedLayerInfo);

                // Set the feature request mode to manual (only manual is currently supported).
                // In this mode, you must manually populate the table - panning and zooming won't request features automatically.
                table.FeatureRequestMode = FeatureRequestMode.ManualCache;

                // Populate the OGC feature collection table.
                QueryParameters queryParamaters = new QueryParameters();
                queryParamaters.MaxFeatures = 1000;
                await table.PopulateFromServiceAsync(queryParamaters, false, null);

                // Create a feature layer from the OGC feature collection table.
                FeatureLayer ogcFeatureLayer = new FeatureLayer(table);

                // Choose a renderer for the layer based on the table.
                ogcFeatureLayer.Renderer = GetRendererForTable(table) ?? ogcFeatureLayer.Renderer;

                // Add the layer to the map.
                _myMapView.Map.OperationalLayers.Add(ogcFeatureLayer);

                // Zoom to the extent of the selected collection.
                if (selectedLayerInfo.Extent is Envelope collectionExtent && !collectionExtent.IsEmpty)
                {
                    await _myMapView.SetViewpointGeometryAsync(collectionExtent, 100);
                }
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex);
                new UIAlertView("Couldn't load layer.", ex.Message, (IUIAlertViewDelegate)null, "OK", null).Show();
            }
            finally
            {
                // Hide the progress bar.
                _loadingProgressBar.StopAnimating();
            }
        }

        private void ShowLayerOptions(object sender, EventArgs e)
        {
            // Create the view controller that will present the list of layers.
            UIAlertController layerSelectionAlert = UIAlertController.Create("Select a layer", "", UIAlertControllerStyle.ActionSheet);

            // Add an option for each layer.
            foreach (OgcFeatureCollectionInfo layerInfo in _serviceInfo.FeatureCollectionInfos)
            {
                // Selecting a layer will call the lambda method, which will show the layer.
                layerSelectionAlert.AddAction(UIAlertAction.Create(layerInfo.Title, UIAlertActionStyle.Default, action => LoadSelectedLayer(layerInfo)));
            }

            // Fix to prevent crash on iPad.
            var popoverPresentationController = layerSelectionAlert.PopoverPresentationController;
            if (popoverPresentationController != null)
            {
                popoverPresentationController.BarButtonItem = _chooseLayersButton;
            }

            // Show the alert.
            PresentViewController(layerSelectionAlert, true, null);
        }

        private Renderer GetRendererForTable(FeatureTable table)
        {
            switch (table.GeometryType)
            {
                case GeometryType.Point:
                case GeometryType.Multipoint:
                    return new SimpleRenderer(new SimpleMarkerSymbol(SimpleMarkerSymbolStyle.Circle, Color.Blue, 4));

                case GeometryType.Polygon:
                case GeometryType.Envelope:
                    return new SimpleRenderer(new SimpleFillSymbol(SimpleFillSymbolStyle.Solid, Color.Blue, null));

                case GeometryType.Polyline:
                    return new SimpleRenderer(new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, Color.Blue, 1));
            }

            return null;
        }

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

            _myMapView = new MapView();
            _myMapView.TranslatesAutoresizingMaskIntoConstraints = false;

            _chooseLayersButton = new UIBarButtonItem();
            _chooseLayersButton.Title = "Choose layer";
            _chooseLayersButton.Enabled = false;

            _loadServiceButton = new UIBarButtonItem { Title = "Load service" };

            UIToolbar toolbar = new UIToolbar();
            toolbar.TranslatesAutoresizingMaskIntoConstraints = false;
            toolbar.Items = new[]
            {
                _loadServiceButton,
                UIBarButtonItem.FlexibleSpaceItem,
                _chooseLayersButton
            };

            _loadingProgressBar = new UIActivityIndicatorView(UIActivityIndicatorViewStyle.WhiteLarge);
            _loadingProgressBar.TranslatesAutoresizingMaskIntoConstraints = false;
            _loadingProgressBar.HidesWhenStopped = true;
            _loadingProgressBar.BackgroundColor = UIColor.FromWhiteAlpha(0, .6f);

            // Add the views.
            View.AddSubviews(_myMapView, toolbar, _loadingProgressBar);

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

                toolbar.TopAnchor.ConstraintEqualTo(_myMapView.BottomAnchor),
                toolbar.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                toolbar.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                toolbar.BottomAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.BottomAnchor),

                _loadingProgressBar.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                _loadingProgressBar.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _loadingProgressBar.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                _loadingProgressBar.BottomAnchor.ConstraintEqualTo(View.BottomAnchor)
            });
        }

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

        public override void ViewWillAppear(bool animated)
        {
            base.ViewWillAppear(animated);

            // Subscribe to events.
            _chooseLayersButton.Clicked += ShowLayerOptions;
            _loadServiceButton.Clicked += ServiceLinkClick;
        }

        private void ServiceLinkClick(object sender, EventArgs e)
        {
            UIAlertView alert = new UIAlertView()
            {
                Message = "Enter OGC API URL.",
                AlertViewStyle = UIAlertViewStyle.PlainTextInput,
                CancelButtonIndex = 1
            };
            alert.AddButton("Load");
            alert.AddButton("Cancel");

            alert.Clicked += (object s, UIButtonEventArgs a) =>
            {
                if (a.ButtonIndex != alert.CancelButtonIndex)
                {
                    LoadService(alert.GetTextField(0).Text);
                }
            };
            alert.Show();
        }

        public override void ViewDidDisappear(bool animated)
        {
            base.ViewDidDisappear(animated);

            // Unsubscribe from events, per best practice.
            _chooseLayersButton.Clicked -= ShowLayerOptions;
            _loadServiceButton.Clicked -= ServiceLinkClick;
        }
    }
}

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