# Creating a location provider for ArcGIS Runtime SDK
Below is an implementation for use with the [ArcGIS Runtime SDK for .NET](http://developers.arcgis.com/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]( https://github.com/dotMorten/NmeaParser/blob/main/src/SampleApp.WinDesktop/NmeaProvider.cs) which uses this to display a map.
**Usage:**
```csharp
NmeaParser.NmeaDevice device = new NmeaParser.NmeaFileDevice("NmeaSampleData.txt");
mapView.LocationDisplay.DataSource = new NmeaLocationProvider(device);
mapView.LocationDisplay.InitialZoomScale = 20000;
mapView.LocationDisplay.IsEnabled = true;
```
**NmeaLocationProvider.cs**
```csharp
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
///
/// Initializes a new instance of the class.
///
/// The NMEA device to monitor
/// Whether starting this datasource also controls the underlying NMEA device
public NmeaLocationDataSource(NmeaParser.NmeaDevice device, bool startStopDevice = true) : this(new GnssMonitor(device), startStopDevice)
{
}
///
/// Initializes a new instance of the class.
///
/// The NMEA device to monitor
/// Whether starting this datasource also controls the underlying NMEA device
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);
}
}
}
}
```
