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 androidx.appcompat.app.AppCompatActivity
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.ActivityMainBinding
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.*
import kotlin.concurrent.timerTask
class MainActivity : AppCompatActivity() {
private val provisionPath: String by lazy {
getExternalFilesDir(null)?.path.toString() + File.separator + getString(R.string.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: ActivityMainBinding by lazy {
DataBindingUtil.setContentView(this, R.layout.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.API_KEY)
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()
}
}