External Position Source Navigation | Maps SDK for Flutter

This example demonstrates how to create a Flutter app that utilizes external position sources for navigation on a map using ``gem_kit``package. The app allows users to navigate to a predefined destination while following the route on the map.

Setup¶

First, get an API key token, see the Getting Started guide.

Prerequisites¶

Make sure you completed the Environment Setup - Flutter Examples guide before starting this guide.

Build and Run¶

Navigate to the external_position_navigation directory within the Flutter examples directory. This is the project folder for this example.

Note - the gem_kit directory containing the Maps SDK for Flutter should be in the plugins directory of the example, e.g. example_pathname/plugins/gem_kit - see the environment setup guide above.

Run: flutter pub get

Configure the native parts:

Android

First, verify that the ANDROID_SDK_ROOT environment variable is set to the root path of your android SDK.

In android/build.gradle add the maven block as shown, within the allprojects block, for both debug and release builds:

allprojects {
    repositories {
        google()
        mavenCentral()
        maven {
           url "${rootDir}/../plugins/gem_kit/android/build"
        }
    }
}

in android/app/build.gradle within the android block, in the defaultConfig block, the android SDK version minSdk must be set as shown below.

Additionally, for release builds, in android/app/build.gradle, within the android block, add the buildTypes block as shown:

Replace example_pathname with the actual project pathname

android {
    defaultConfig {
        applicationId "com.magiclane.gem_kit.examples.example_pathname"
        minSdk 21
        targetSdk flutter.targetSdk
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
    }
    buildTypes {
        release {
            minifyEnabled false
            shrinkResources false

            // TODO: Add your own signing config for the release build.
            // Signing with the debug keys for now, so `flutter run --release` works.
            signingConfig signingConfigs.debug
        }
    }
}

iOS

In the ios/Podfile configuration file, at the top, set the minimum ios platform version to 14 like this:

platform :ios, '14.0'

We recommend you to run these commands after you copy the gem_kit into your project: |flutter clean |flutter pub get |and |cd ios |pod install

Then run the project:

flutter run --debug

or

flutter run --release

App entry and initialization¶

const projectApiToken = String.fromEnvironment('GEM_TOKEN');

void main() {
  runApp(const MyApp());
}

This code initializes the projectApiToken with the required authorization token and launches the app.

How It Works¶

The example app demonstrates the following features:

Uses GemKit SDK to initialize the map.
Implements navigation using external position sources.
Allows route building and starts navigation with real-time position updates.

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'External Position Source Navigation',
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  late GemMapController _mapController;
  late NavigationInstruction currentInstruction;
  bool _areRoutesBuilt = false;
  bool _isNavigationActive = false;
  bool _hasDataSource = false;
  final DataSource _dataSource = DataSource([DataType.position]);

  @override
  void dispose() {
    GemKit.release();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("ExternalPositionNavigation",
            style: TextStyle(color: Colors.white)),
        backgroundColor: Colors.deepPurple[900],
        actions: [
          if (!_isNavigationActive && _areRoutesBuilt)
            IconButton(
              onPressed: () => _startNavigation(),
              icon: const Icon(Icons.play_arrow, color: Colors.white),
            ),
          if (_isNavigationActive)
            IconButton(
              onPressed: _stopNavigation,
              icon: const Icon(
                Icons.stop,
                color: Colors.white,
              ),
            ),
          if (!_areRoutesBuilt && _hasDataSource)
            IconButton(
              onPressed: () => _onBuildRouteButtonPressed(context),
              icon: const Icon(
                Icons.route,
                color: Colors.white,
              ),
            ),
          if (!_isNavigationActive)
            IconButton(
                onPressed: _onFollowPositionButtonPressed,
                icon: const Icon(
                  Icons.location_searching_sharp,
                  color: Colors.white,
                ))
        ],
      ),
      body: Stack(children: [
        GemMap(
          onMapCreated: _onMapCreated,
        ),
        if (_isNavigationActive)
          Positioned(
            top: 10,
            left: 10,
            child: Column(children: [
              NavigationInstructionPanel(
                instruction: currentInstruction,
              ),
              const SizedBox(
                height: 10,
              ),
              FollowPositionButton(
                onTap: () => _mapController.startFollowingPosition(),
              ),
            ]),
          ),
        if (_isNavigationActive)
          Positioned(
            bottom: MediaQuery.of(context).padding.bottom + 10,
            left: 0,
            child: NavigationBottomPanel(
              remainingDistance:
                  currentInstruction.getFormattedRemainingDistance(),
              remainingDuration:
                  currentInstruction.getFormattedRemainingDuration(),
              eta: currentInstruction.getFormattedETA(),
            ),
          ),
      ]),
      resizeToAvoidBottomInset: false,
    );
  }
}

This code sets up the user interface, including a map and navigation buttons.

void _onBuildRouteButtonPressed(BuildContext context) {
  final departureLandmark =
      Landmark.withLatLng(latitude: 34.915646, longitude: -110.147933);
  final destinationLandmark =
      Landmark.withLatLng(latitude: 34.933105, longitude: -110.131363);
  final routePreferences = RoutePreferences();
  _showSnackBar(context, message: 'The route is calculating.');

  _routingHandler = RoutingService.calculateRoute(
      [departureLandmark, destinationLandmark], routePreferences,
      (err, routes) {
    _routingHandler = null;
    ScaffoldMessenger.of(context).clearSnackBars();

    if (err == GemError.routeTooLong) {
      print('The destination is too far from your current location. Change the coordinates of the destination.');
      return;
    }

    if (err == GemError.success) {
      final routesMap = _mapController.preferences.routes;
      for (final route in routes!) {
        routesMap.add(route, route == routes.first,
            label: route.getMapLabel());
      }
      _mapController.centerOnRoutes(routes: routes);
      setState(() {
        _areRoutesBuilt = true;
      });
    }
  });
}

This code handles building the route from a departure point to a destination, notifying the user when the calculation is in progress.

Future<void> _startNavigation() async {
  final routes = _mapController.preferences.routes;
  _navigationHandler = NavigationService.startNavigation(routes.mainRoute,
      (type, instruction) {
    if (type == NavigationEventType.destinationReached ||
        type == NavigationEventType.error) {
      PositionService.instance.removeDataSource();
      _dataSource.stop();
      setState(() {
        _isNavigationActive = false;
        _cancelRoute();
      });
      _stopNavigation();
      return;
    }
    _isNavigationActive = true;
    if (instruction != null) {
      setState(() => currentInstruction = instruction);
    }
  });

  _mapController.startFollowingPosition();
  await _pushExternalPosition();
}

This method starts the navigation and sets the map to follow the user’s position.

Pushing External Position Data¶

Future<void> _pushExternalPosition() async {
  final route = _mapController.preferences.routes.mainRoute;
  final distance = route.getTimeDistance().totalDistanceM;
  Coordinates prevCoordinates = route.getCoordinateOnRoute(0);

  for (int currentDistance = 1;
      currentDistance <= distance;
      currentDistance += 1) {
    if (!_hasDataSource) return;

    if (currentDistance == distance) {
      _stopNavigation();
      return;
    }

    final currentCoordinates = route.getCoordinateOnRoute(currentDistance);
    await Future<void>.delayed(Duration(milliseconds: 25));
    _dataSource.pushData(
        positionData: ExternalPositionData(
            timestamp: DateTime.now().toUtc().millisecondsSinceEpoch,
            latitude: currentCoordinates.latitude,
            longitude: currentCoordinates.longitude,
            altitude: 0,
            heading: _getHeading(prevCoordinates, currentCoordinates),
            speed: 0));
    prevCoordinates = currentCoordinates;
  }
}

This code manages the position data, updating the user’s location along the route at regular intervals.

Flutter Examples¶

Maps SDK for Flutter Examples can be downloaded or cloned with Git

External Position Source Navigation¶