android maps auto-rotate

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

@Overridepublic 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

    @Overridepublic 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));}

I have successfully implemented aleph_null solution and here I will add some details that are not mentioned in the accepted solution:

For the above solution to work you need to implement android.hardware.SensorEventListener interface.

You need also to register to the SensorEventListener in your onResume and onPause methods as follow:

@Override    protected void onResume() {     super.onResume();     mSensorManager.registerListener(this,             mRotVectSensor,             SensorManager.SENSOR_STATUS_ACCURACY_LOW);    }@Overrideprotected void onPause() {    // unregister listener    super.onPause();    mSensorManager.unregisterListener(this);}

Note to "@Bytecode": To avoid flickering, use low value for the sampling period, something like SensorManager.SENSOR_STATUS_ACCURACY_LOW.

I have noticed also that the sensor sends sometime more data than the device can handle and as a result, the map camera starts to move in a strange way!

To control the amount of data handled by onSensorChanged, I suggest the following implementation:

@Overridepublic 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);        if (Math.abs(Math.toDegrees(orientation[0]) - angle) > 0.8) {            float bearing = (float) Math.toDegrees(orientation[0]) + mDeclination;            updateCamera(bearing);        }        angle = Math.toDegrees(orientation[0]);    }}

It is possible by registering your application with Sensor Listener for Orientation and getting the angle relative to true north inside onSensorChanged and update camera accordingly.Angle can be used for bearing. The following code can be used:

Instead of using Sensor.TYPE_ORIENTATION try using getOrinetation api. Sensor.TYPE_ORIENTATIONhas been deprecated.@Overrideprotected void onResume() {    // TODO Auto-generated method stub    super.onResume();    if (sensorManager != null)        sensorManager.registerListener(this,                sensorManager.getDefaultSensor(Sensor.TYPE_ORIENTATION),                SensorManager.SENSOR_DELAY_GAME);}public void onSensorChanged(SensorEvent event) {    float degree = Math.round(event.values[0]);    Log.d(TAG, "Degree ---------- " + degree);    updateCamera(degree);}private void updateCamera(float bearing) {    CameraPosition oldPos = googleMap.getCameraPosition();    CameraPosition pos = CameraPosition.builder(oldPos).bearing(bearing)            .build();    googleMap.moveCamera(CameraUpdateFactory.newCameraPosition(pos));}