ArcGISRuntime.md

Creating a location provider for ArcGIS Runtime SDK

Below is an implementation for use with the ArcGIS Runtime SDK for .NET. Use this location provider on the MapView's LocationDisplay to send it location data from your NMEA device to display your current location on a map.

Below is an example implementation of this. You can also check out the Desktop Sample app in the Github Repo which uses this to display a map.

Usage:

NmeaParser.NmeaDevice device = new NmeaParser.NmeaFileDevice("NmeaSampleData.txt");
mapView.LocationDisplay.DataSource = new NmeaLocationProvider(device);
mapView.LocationDisplay.InitialZoomScale = 20000;
mapView.LocationDisplay.IsEnabled = true;

NmeaLocationProvider.cs

using System.Threading.Tasks;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Location;
using NmeaParser;

namespace NmeaParser.ArcGIS
{
    public class NmeaLocationProvider : LocationDataSource
    {
        private readonly NmeaParser.NmeaDevice device;

        public NmeaLocationProvider(NmeaParser.NmeaDevice device)
        {
            this.device = device;
            device.MessageReceived += NmeaMessageReceived;
        }

        private void NmeaMessageReceived(object sender, NmeaMessageReceivedEventArgs e)
        {
            var message = e.Message;
            if (message is NmeaParser.Messages.Rmc rmc && rmc.Active)
            {
                base.UpdateLocation(new Location(
                    new MapPoint(rmc.Longitude, rmc.Latitude, SpatialReferences.Wgs84),
                    horizontalAccuracy: double.NaN,
                    velocity: double.IsNaN(rmc.Speed) ? 0 : rmc.Speed,
                    course: double.IsNaN(rmc.Course) ? 0 : rmc.Course, // Current ArcGIS Runtime limitation that course can't be NaN
                    isLastKnown: false));
            }
        }
        protected override Task OnStartAsync() => device.OpenAsync();

        protected override Task OnStopAsync() => device.CloseAsync();
    }
}

Combining multiple NMEA messages into a single location event

NMEA often happens in a burst of messages, which could be combined to one larger location object with more information available, as well as containing information from multiple different satellite systems. By using the GnssMonitor class that aggregates these messages, we can create a much more robust location provider:

using System;
using System.Threading.Tasks;
using Esri.ArcGISRuntime.Geometry;
using NmeaParser.Gnss;

namespace NmeaParser.ArcGIS
{
   public class NmeaLocationDataSource : Esri.ArcGISRuntime.Location.LocationDataSource
    {
        private static SpatialReference wgs84_ellipsoidHeight = SpatialReference.Create(4326, 115700);
        private readonly GnssMonitor m_gnssMonitor;
        private readonly bool m_startStopDevice;
        private double lastCourse = 0; // Course can fallback to NaN, but ArcGIS Datasource don't allow NaN course, so we cache last known as a fallback

        /// <summary>
        /// Initializes a new instance of the <see cref="NmeaLocationDataSource"/> class.
        /// </summary>
        /// <param name="device">The NMEA device to monitor</param>
        /// <param name="startStopDevice">Whether starting this datasource also controls the underlying NMEA device</param>
        public NmeaLocationDataSource(NmeaParser.NmeaDevice device, bool startStopDevice = true) : this(new GnssMonitor(device), startStopDevice)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="NmeaLocationDataSource"/> class.
        /// </summary>
        /// <param name="monitor">The NMEA device to monitor</param>
        /// <param name="startStopDevice">Whether starting this datasource also controls the underlying NMEA device</param>
        public NmeaLocationDataSource(NmeaParser.Gnss.GnssMonitor monitor, bool startStopDevice = true)
        {
            if (monitor == null)
                throw new ArgumentNullException(nameof(monitor));
            this.m_gnssMonitor = monitor;
            m_startStopDevice = startStopDevice;
        }

        protected async override Task OnStartAsync()
        {
            m_gnssMonitor.LocationChanged += OnLocationChanged;
            m_gnssMonitor.LocationLost += OnLocationChanged;
            if (m_startStopDevice && !this.m_gnssMonitor.Device.IsOpen)
                await this.m_gnssMonitor.Device.OpenAsync();

            if (m_gnssMonitor.IsFixValid)
                OnLocationChanged(this, EventArgs.Empty);
        }

        protected override Task OnStopAsync()
        {
            m_gnssMonitor.LocationChanged -= OnLocationChanged;
            m_gnssMonitor.LocationLost -= OnLocationChanged;
            if(m_startStopDevice)
                return m_gnssMonitor.Device.CloseAsync();
            else
                return Task.CompletedTask;
        }

        private Esri.ArcGISRuntime.Location.Location currentLocation;

        private void OnLocationChanged(object sender, EventArgs e)
        {
            if (double.IsNaN(m_gnssMonitor.Longitude) || double.IsNaN(m_gnssMonitor.Latitude)) return;
            if (!double.IsNaN(m_gnssMonitor.Course))
                lastCourse = m_gnssMonitor.Course;
            DateTimeOffset? timestamp = null;
            if(m_gnssMonitor.FixTime.HasValue)
                timestamp = new DateTimeOffset(DateTime.UtcNow.Date.Add(m_gnssMonitor.FixTime.Value));
            var location = new Esri.ArcGISRuntime.Location.Location(
                timestamp: timestamp,
                position: !double.IsNaN(m_gnssMonitor.Altitude) ? new MapPoint(m_gnssMonitor.Longitude, m_gnssMonitor.Latitude, m_gnssMonitor.Altitude, wgs84_ellipsoidHeight) : new MapPoint(m_gnssMonitor.Longitude, m_gnssMonitor.Latitude, SpatialReferences.Wgs84),
                horizontalAccuracy: m_gnssMonitor.HorizontalError,
                verticalAccuracy: m_gnssMonitor.VerticalError,
                velocity: double.IsNaN(m_gnssMonitor.Speed) ? 0 : m_gnssMonitor.Speed * 0.51444444,
                course: lastCourse,
                !m_gnssMonitor.IsFixValid);
            // Avoid raising additional location events if nothing changed
            if (currentLocation == null ||
                currentLocation.Position.X != location.Position.X ||
                currentLocation.Position.Y != location.Position.Y ||
                currentLocation.Position.Z != location.Position.Z ||
                currentLocation.Course != location.Course ||
                currentLocation.Velocity != location.Velocity ||
                currentLocation.HorizontalAccuracy != location.HorizontalAccuracy ||
                currentLocation.VerticalAccuracy != location.VerticalAccuracy ||
                currentLocation.IsLastKnown != location.IsLastKnown ||
                timestamp != location.Timestamp)
            {                
                currentLocation = location;
                UpdateLocation(currentLocation);
            }
        }
    }
}