This sample demonstrates how to parse NMEA sentences and use the results to show device location on the map.
Use case
NMEA sentences can be retrieved from GPS receivers and parsed into a series of coordinates with additional information. Devices without a built-in GPS receiver can retrieve NMEA sentences by using a separate GPS dongle, commonly connected via bluetooth or through a serial port.
The NMEA location data source allows for detailed interrogation of the information coming from the GPS receiver. For example, allowing you to report the number of satellites in view.
How to use the sample
Click floating button "Play" to parse the provided NMEA sentences into a location data source, and display the location position and related satellite information. Click "Stop" to stop displaying the location information. The sample will automatically re-center the location data source as it moves across the map.
How it works
- Load NMEA sentences from a local file.
- Parse the NMEA sentence strings, and push data into
NmeaLocationDataSource. - Set the
NmeaLocationDataSourceto theLocationDisplay's data source. - Start the location display to begin receiving location and satellite updates.
Relevant API
- LocationDisplay
- NmeaLocationDataSource
- NmeaSatelliteInfo
About the data
This sample reads lines from a local file to simulate the feed of data into the NmeaLocationDataSource. This simulated data source provides NMEA data periodically, and allows the sample to be used on devices without a GPS dongle that produces NMEA data.
The route taken in this sample features a one minute driving trip around Redlands, CA.
Tags
GPS, history, navigation, NMEA, real-time, trace
Sample Code
/* 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. * */ package com.esri.arcgismaps.sample.displaydevicelocationwithnmeadatasources import android.os.Bundle import android.util.Log import android.view.View import android.widget.TextView import com.esri.arcgismaps.sample.sampleslib.EdgeToEdgeCompatActivity import androidx.appcompat.content.res.AppCompatResources import androidx.databinding.DataBindingUtil import androidx.lifecycle.lifecycleScope import com.arcgismaps.ApiKey import com.arcgismaps.ArcGISEnvironment import com.arcgismaps.geometry.Point import com.arcgismaps.geometry.SpatialReference import com.arcgismaps.location.LocationDataSourceStatus import com.arcgismaps.location.LocationDisplayAutoPanMode import com.arcgismaps.location.NmeaGnssSystem import com.arcgismaps.location.NmeaLocationDataSource import com.arcgismaps.mapping.ArcGISMap import com.arcgismaps.mapping.BasemapStyle import com.arcgismaps.mapping.Viewpoint import com.esri.arcgismaps.sample.displaydevicelocationwithnmeadatasources.databinding.DisplayDeviceLocationWithNmeaDataSourcesActivityMainBinding import com.google.android.material.floatingactionbutton.FloatingActionButton import com.google.android.material.snackbar.Snackbar import kotlinx.coroutines.launch import java.io.File import java.nio.charset.StandardCharsets import java.util.Timer import kotlin.concurrent.timerTask class MainActivity : EdgeToEdgeCompatActivity() { private val provisionPath: String by lazy { getExternalFilesDir(null)?.path.toString() + File.separator + getString(R.string.display_device_location_with_nmea_data_sources_app_name) } // create a new NMEA location data source private val nmeaLocationDataSource: NmeaLocationDataSource = NmeaLocationDataSource(SpatialReference.wgs84()) // create a timer to simulate a stream of NMEA data private var timer = Timer() // list of nmea location sentences private var nmeaSentences: List<String>? = emptyList() // index of nmea location sentence private var locationIndex = 0 // set up data binding for the activity private val activityMainBinding: DisplayDeviceLocationWithNmeaDataSourcesActivityMainBinding by lazy { DataBindingUtil.setContentView(this, R.layout.display_device_location_with_nmea_data_sources_activity_main) } private val mapView by lazy { activityMainBinding.mapView } private val accuracyTV: TextView by lazy { activityMainBinding.accuracyTV } private val satelliteCountTV: TextView by lazy { activityMainBinding.satelliteCountTV } private val satelliteIDsTV: TextView by lazy { activityMainBinding.satelliteIDsTV } private val systemTypeTV: TextView by lazy { activityMainBinding.systemTypeTV } private val playPauseFAB: FloatingActionButton by lazy { activityMainBinding.playPauseFAB } override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) // authentication with an API key or named user is // required to access basemaps and other location services ArcGISEnvironment.apiKey = ApiKey.create(BuildConfig.ACCESS_TOKEN) lifecycle.addObserver(mapView) // create and add a map with a navigation night basemap style val map = ArcGISMap(BasemapStyle.ArcGISNavigationNight) mapView.map = map // set a viewpoint on the map view centered on Redlands, California mapView.setViewpoint( Viewpoint( Point(-117.191, 34.0306, SpatialReference.wgs84()), 100000.0 ) ) mapView.locationDisplay.apply { // set the map view's location display to use the nmea location data source dataSource = nmeaLocationDataSource // set the map view to recenter on location changed events setAutoPanMode(LocationDisplayAutoPanMode.Recenter) } // disable map view interaction, the location display will automatically center on the mock device location mapView.interactionOptions.apply { isPanEnabled = false isZoomEnabled = false isRotateEnabled = false } // read nmea location sentences from file nmeaSentences = getNMEASentenceList() // collects the accuracy for each location change collectLocationChanges() // collects satellite changes and display satellite information collectSatelliteChanges() } /** * Reads NMEA location sentences from the .nmea file and * returns it as a [MutableList] */ private fun getNMEASentenceList(): List<String>? { val simulatedNmeaDataFile = File("$provisionPath/Redlands.nmea") if (!simulatedNmeaDataFile.exists()) { showError("NMEA file does not exist") return null } // create list of nmea location sentences var nmeaSentences: List<String> = emptyList() // create a buffered reader using the .nmea file val bufferedReader = File(simulatedNmeaDataFile.path).bufferedReader() // read the nmea file contents using a buffered reader and store the mock data sentences in a list bufferedReader.useLines { bufferReaderLines -> // add carriage return for nmea location data source parser nmeaSentences = bufferReaderLines.map { it + "\n" }.toList() } return nmeaSentences } /** * Control the start/stop status of the NMEA location data source */ fun playPauseClick(view: View) = lifecycleScope.launch { if (nmeaLocationDataSource.status.value != LocationDataSourceStatus.Started) { // initialize the location data source and prepare to begin receiving location updates when data is pushed // as updates are received, they will be displayed on the map nmeaLocationDataSource.start().onFailure { showError("NmeaLocationDataSource failed to start: ${it.message}") return@launch } // starts the NMEA mock data sentences nmeaSentences?.let { startNMEAMockData(it) } setButtonStatus(true) } else { // stop receiving and displaying location data nmeaLocationDataSource.stop() // cancel up the timer task timer.cancel() setButtonStatus(false) clearUI() } } /** * Initializes the location data source, reads the mock data NMEA sentences, and displays location updates from that file * on the location display. Data is pushed to the data source using a timeline to simulate live updates, as they would * appear if using real-time data from a GPS dongle */ /** * Push the mock data NMEA sentences into the data source every 250 ms */ private fun startNMEAMockData(nmeaSentences: List<String>) { timer = Timer() timer.schedule(timerTask { // only push data when started if (nmeaLocationDataSource.status.value == LocationDataSourceStatus.Started) nmeaLocationDataSource.pushData( nmeaSentences[locationIndex++].toByteArray(StandardCharsets.UTF_8) ) // reset the location index after the last data point is reached if (locationIndex == nmeaSentences.size) locationIndex = 0 }, 250, 250) } /** * Sets the FAB button to "Start"/"Stop" based on [isShowingLocation] */ private fun setButtonStatus(isShowingLocation: Boolean) = if (isShowingLocation) { playPauseFAB.setImageDrawable( AppCompatResources.getDrawable( this, R.drawable.ic_round_pause_24 ) ) } else { playPauseFAB.setImageDrawable( AppCompatResources.getDrawable( this, R.drawable.ic_round_play_arrow_24 ) ) } /** * Collects location changes of the NMEA location data source, * and displays the location accuracy */ private fun collectLocationChanges() = lifecycleScope.launch { nmeaLocationDataSource.locationChanged.collect { nmeaLocation -> // convert from meters to foot val horizontalAccuracy = nmeaLocation.horizontalAccuracy * 3.28084 val verticalAccuracy = nmeaLocation.verticalAccuracy * 3.28084 accuracyTV.text = getString(R.string.accuracy) + "Horizontal-%.1fft, Vertical-%.1fft".format( horizontalAccuracy, verticalAccuracy ) } } /** * Obtains NMEA satellite information from the NMEA location data source, * and displays satellite information on the app */ private fun collectSatelliteChanges() = lifecycleScope.launch { nmeaLocationDataSource.satellitesChanged.collect { nmeaSatelliteInfoList -> // set the text of the satellite count label satelliteCountTV.text = getString(R.string.satellite_count) + nmeaSatelliteInfoList.size // get the system of the first satellite val satelliteSystems = when (nmeaSatelliteInfoList.first().system) { NmeaGnssSystem.Bds -> "BDS" NmeaGnssSystem.Galileo -> "Galileo" NmeaGnssSystem.Glonass -> "Glonass" NmeaGnssSystem.Gps -> "GPS" NmeaGnssSystem.NavIc -> "NavIc" NmeaGnssSystem.Qzss -> "Qzss" NmeaGnssSystem.Unknown -> "Unknown" } // get the satellite IDs from the info list val uniqueSatelliteIDs = nmeaSatelliteInfoList.map { it.id } // display the satellite system and id information systemTypeTV.text = getString(R.string.system) + satelliteSystems satelliteIDsTV.text = getString(R.string.satellite_ids) + uniqueSatelliteIDs } } /** * Clears out the info messages when LocationDataSource is paused. */ private fun clearUI() { accuracyTV.text = getString(R.string.accuracy) satelliteCountTV.text = getString(R.string.satellite_count) satelliteIDsTV.text = getString(R.string.satellite_ids) systemTypeTV.text = getString(R.string.system) } private fun showError(message: String) { Log.e(localClassName, message) Snackbar.make(mapView, message, Snackbar.LENGTH_SHORT).show() } }