Navigate Route

In this guide, you will learn how to compute a route between a departure point and a destination point, render the route on an interactive map, and then navigate along the route.

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

Go to the navigate_route directory within the Flutter examples directory - that is the name of this example project.

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

Import Necessary Packages

import 'package:gem_kit/core.dart';
import 'package:gem_kit/map.dart';
import 'package:gem_kit/navigation.dart';
import 'package:gem_kit/routing.dart';
import 'package:gem_kit/sense.dart';

import 'bottom_navigation_panel.dart';
import 'top_navigation_panel.dart';
import 'utility.dart';

import 'package:permission_handler/permission_handler.dart';

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart' hide Route, Animation;

The dart material package is imported, as well as the required gem_kit packages.

The permission handler is used to request location (GPS) sensor permission from the user, if it was not previously granted, as this is required for navigation.

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

Map Initialization

void _onMapCreated(GemMapController controller) {
  // Save controller for further usage.
  _mapController = controller;
}

This callback function is called when the interactive map is initialized and ready to use.

Building the Route

void _onBuildRouteButtonPressed(BuildContext context) {
  if (_currentLocation == null) {
    _showSnackBar(context,
        message: 'Current location is needed to compute the route.', duration: const Duration(seconds: 3));
    return;
  }

  // Define the departure
  final departureLandmark = Landmark.withCoordinates(_currentLocation!);

  // Define the destination.
  final destinationLandmark = Landmark.withLatLng(latitude: 52.51614, longitude: 13.37748);

  // Define the route preferences.
  final routePreferences = RoutePreferences();
  _showSnackBar(context, message: 'The route is calculating.');

  // Calling the calculateRoute SDK method.
  _routingHandler =
      RoutingService.calculateRoute([departureLandmark, destinationLandmark], routePreferences, (err, routes) {
    // If the route calculation is finished, we don't have a progress listener anymore.
    _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 there aren't any errors, we display the routes.
    if (err == GemError.success) {
      // Get the routes collection from map preferences.
      final routesMap = _mapController.preferences.routes;

      // Display the routes on map.
      for (final route in routes!) {
        routesMap.add(route, route == routes.first, label: route.getMapLabel());
      }

      // Center the camera on routes.
      _mapController.centerOnRoutes(routes);
      setState(() {
        _areRoutesBuilt = true;
      });
    }
  });
}

When the route button in the upper right corner is pressed, a route is computed from the current position to a preset location in Europe.

A route must have at least two waypoints, one for the departure, and one for the destination. Optionally, zero or more intermediate waypoints may be specified through which the route will pass, in order from departure to destination.

Each waypoint is a Landmark and has latitude and longitude coordinates.

In this case, the current location is obtained and set in the departure landmark waypoint:

final departureLandmark = Landmark.withCoordinates(_currentLocation!);

and the destination is set to preset coordinates:

final destinationLandmark = Landmark.withLatLng(latitude: 52.51614, longitude: 13.37748);

then the route is calculated:

RoutingService.calculateRoute()

If there are no errors, the list of resulting routes (as there may be a few alternatives) is added to the map:

routesMap.add()

the first resulting route is auto-selected as the main route, and then the map is centered on the resulting routes, such that they fit in the viewport:

_mapController.centerOnRoutes(routes);

Starting Navigation

void _startNavigation() {
  final routes = _mapController.preferences.routes;

  _navigationHandler = NavigationService.startNavigation(routes.mainRoute, (type, instruction) async {
    if (type == NavigationEventType.destinationReached || type == NavigationEventType.error) {
      // If the navigation has ended or if an error occurred while navigating, remove routes.
      setState(() {
        _isNavigationActive = false;
        _cancelRoute();
      });
      return;
    }
    _isNavigationActive = true;

    if (instruction != null) {
      setState(() => currentInstruction = instruction);
    }
  });

  // Set the camera to follow position.
  _mapController.startFollowingPosition();
}

Once a route is computed, tapping the play button in the upper right starts navigation on the selected route.

Following the Position

void _onFollowPositionButtonPressed() async {
  if (kIsWeb) {
    // On web platform permissions are handled differently than other platforms.
    // The SDK handles the request for permission for location.
    _locationPermissionStatus = PermissionStatus.granted;
  } else {
    // For Android & iOS platforms, permission_handler package is used to ask for permissions.
    _locationPermissionStatus = await Permission.locationWhenInUse.request();
  }

  if (_locationPermissionStatus == PermissionStatus.granted) {
    // After the permission was granted, we can set the live data source (in most cases the GPS).
    // The data source should be set only once; otherwise, we'll get -5 error.
    if (!_hasLiveDataSource) {
      PositionService.instance.setLiveDataSource();
      _getCurrentLocation();
      _hasLiveDataSource = true;
    }

    // After the data source is set, startFollowingPosition can be safely called.
    // Optionally, we can set an animation
    final animation = GemAnimation(type: AnimationType.linear);

    // Calling the start following position SDK method.
    _mapController.startFollowingPosition(animation: animation);
  }
  setState(() {});
}

Follow position means the camera tracks the position of the phone/device, indicated by an arrow moving along the route on the map.

_mapController.startFollowingPosition();

Note that if location (GPS sensor) permission was not previously granted, the app will ask for location permission from the user, as this is required for navigation.

_locationPermissionStatus = await Permission.locationWhenInUse.request();

Once permission is granted by the user, it is possible to set the location (GPS sensor) as the data source for the phone/device position on the map:

PositionService.instance.setLiveDataSource();

If the user pans the map away from the route, clicking the Re-center button starts following position again.

Flutter Examples

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