appml/AndroidBearingExample

Full example to calculate bearing in Android

Android Bearing Example

Full example to calculate bearing in Android, useful in augmented reality apps.

I wrote this example to thank you to all users that have posted in interner some kind of solution to solve bearing calculation.

The "engine" is BearingSensor class that initializes sensors, get data from them and apply some formulas to received data:

Sensors initialization

BearingSensor class initializes and uses these sensors: gravity, accelerometer and magnetometer sensors.

this.mGravity = this.mSensorManager.getDefaultSensor( Sensor.TYPE_GRAVITY );
haveGravity = this.mSensorManager.registerListener( mSensorEventListener, this.mGravity, SensorManager.SENSOR_DELAY_GAME );

this.mAccelerometer = this.mSensorManager.getDefaultSensor( Sensor.TYPE_ACCELEROMETER );
haveAccelerometer = this.mSensorManager.registerListener( mSensorEventListener, this.mAccelerometer, SensorManager.SENSOR_DELAY_GAME );

this.mMagnetometer = this.mSensorManager.getDefaultSensor( Sensor.TYPE_MAGNETIC_FIELD );
haveMagnetometer = this.mSensorManager.registerListener( mSensorEventListener, this.mMagnetometer, SensorManager.SENSOR_DELAY_GAME );

Get orientation

BearingSensor class retrieves data using SensorManager listener:

@Override
public void onAccuracyChanged( Sensor sensor, int accuracy );

@Override
public void onSensorChanged( SensorEvent event );

onAccuracyChanged is not important, so its body is empty.

In onSensorChanged we get data from sensors and apply some formulas on them, using

SensorManager.getRotationMatrix

to obtain rotation matrix from sensor data, then

SensorManager.remapCoordinateSystem

to apply a remapping of coordinate system due to device orientation, finally

SensorManager.getOrientation

to compute the device's orientation based on the rotation matrix.

How to use BearingSensor class

To use BearingSensor you have to instantiate it passing a context instance and the listener that will receive bearing changes.

public class MainActivity extends AppCompatActivity implements BearingSensor.BearingSensorListener {

  private BearingSensor bearingSensor;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);

      bearingSensor = new BearingSensor(this, this);
  }

  @Override
  public void onBearingSensorAngleChanged(int azimuth) {
      Log.i("BearingSensor", String.format("%d degrees", azimuth));
  }

  @Override
  public void onResume()
  {
      super.onResume();
      bearingSensor.start();
  }

  @Override
  public void onPause()
  {
      super.onPause();
      bearingSensor.stop();
  }
}

The callback

public void onBearingSensorAngleChanged(int azimuth);

contains azimuth parameter that indicates current angle from north pole in degrees.

Example app output