android maps auto-rotate

Question

If you open the Google maps app, there is a button on the top right of the screen that you can press to center the map on your current location. The button\'s icon then chan

Answer 1

Ok here's how I think it should be done a year later. Please correct me if you spot any issues.

Most of the following code deals with a discrepancy between coordinate systems. I'm using a rotation vector sensor. From the docs: Y is tangential to the ground at the device's current location and points towards magnetic north. Bearing in google maps, on the other hand, seems to point to true north. this page shows how the conversion is done

1) get the current declination from your current GPS location

@Override
public void onLocationChanged(Location location) {
    GeomagneticField field = new GeomagneticField(
            (float)location.getLatitude(),
            (float)location.getLongitude(),
            (float)location.getAltitude(),
            System.currentTimeMillis()
        );

    // getDeclination returns degrees
    mDeclination = field.getDeclination();
} 

2) calculate bearing from declination and magnetic north

    @Override
public void onSensorChanged(SensorEvent event) {
    if(event.sensor.getType() == Sensor.TYPE_ROTATION_VECTOR) {
        SensorManager.getRotationMatrixFromVector(
                mRotationMatrix , event.values);
        float[] orientation = new float[3];
        SensorManager.getOrientation(mRotationMatrix, orientation);
        float bearing = Math.toDegrees(orientation[0]) + mDeclination;
        updateCamera(bearing);  
    }
}

3) update maps

private void updateCamera(float bearing) {
    CameraPosition oldPos = mMap.getCameraPosition();

    CameraPosition pos = CameraPosition.builder(oldPos).bearing(bearing).build();
            mMap.moveCamera(CameraUpdateFactory.newCameraPosition(pos));
}