Map Compass

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This example demonstrates how to render a compass icon that displays the heading rotation of an interactive map. The compass indicates the direction where 0 degrees is north, 90 degrees is east, 180 degrees is south, and 270 degrees is west. You will also learn how to rotate the map back to its default north-up orientation.

How it works

The example app demonstrates the following features:

• Display a map and sync a compass to its rotation.
• Align north up the map.

Initial map rotation angle, north pointing up

Map rotation angle changed, north pointing differently

Map and UI components display

main.dart

class _MyHomePageState extends State<MyHomePage> {
  late GemMapController mapController;

  double compassAngle = 0;
  Uint8List? compassImage;

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.deepPurple[900],
        title: const Text("Map Compass", style: TextStyle(color: Colors.white)),
      ),
      body: Stack(
        children: [
          GemMap(
            key: ValueKey("GemMap"),
            onMapCreated: _onMapCreated,
            appAuthorization: projectApiToken,
          ),
          if (compassImage != null)
            Positioned(
              right: 12,
              top: 12,
              child: InkWell(
                // Align the map north to up.
                onTap: () => mapController.alignNorthUp(),
                child: Transform.rotate(
                  angle: -compassAngle * (3.141592653589793 / 180),
                  child: Container(
                    padding: const EdgeInsets.all(3),
                    decoration: const BoxDecoration(
                      shape: BoxShape.circle,
                      color: Colors.white,
                    ),
                    child: SizedBox(
                        width: 40,
                        height: 40,
                        child: Image.memory(
                          compassImage!,
                          gaplessPlayback: true,
                      ),
                    ),
                  ),
                ),
              ),
            ),
        ],
      ),
    );
  }

  // The callback for when map is ready to use.
  void _onMapCreated(GemMapController controller) {
    mapController = controller;

    // Register the map angle update callback.
    mapController.registerMapAngleUpdateCallback(
      (angle) => setState(() => compassAngle = angle),
    );

    setState(() {
      compassImage = _compassImage();
    });
  }

  Uint8List? _compassImage() {
    // We will use the SDK image for compass but any widget can be used to represent the compass.
    final image = SdkSettings.getImageById(
      id: EngineMisc.compassEnableSensorOFF.id,
      size: const Size(100, 100),
    );
    return image;
  }
}

This callback function is triggered when the interactive map is initialized and ready for use. The map angle update callback is registered to ensure that the compass icon reflects the map’s current heading.

When the map’s heading angle changes (e.g., due to rotation), the compassAngle variable is updated, causing the compass widget to rotate accordingly. Tapping on the compass icon calls mapController.alignNorthUp() , which reorients the map so that 0 degrees (north) is at the top of the screen.