Android Compass Bearing

Question

I am trying to get the compass bearing in degrees (i.e. 0-360) using the following method:

float[] mGravity;
float[] mGeomagnetic;
public void onSensorChanged(SensorEvent event) {
    if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER)
        mGravity = event.values;
    if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD)
        mGeomagnetic = event.values;
    if (mGravity != null && mGeomagnetic != null) {
        float R[] = new float[9];
        float I[] = new float[9];
        boolean success = SensorManager.getRotationMatrix(R, I, mGravity,
                mGeomagnetic);
        if (success) {
            float orientation[] = new float[3];
            SensorManager.getOrientation(R, orientation);
            float azimut = orientation[0];
            bearing.setText("Bearing: "+ azimut);
        }
    }
}

The azimuth value (i.e. orientation[0]) should be 0<=azimuth<360 but I am getting only values from -3 to 3 as I rotate my device. Can someone please tell me what the problem might be please?

Answer 1

It is true that it is in Radians. Thanks Hoan. I added some logic to get that bearing in degrees from 0 to 360 becuase if I only converted it to degrees, I was getting values from -180 to 180.

float azimuthInRadians = orientation[0];
float azimuthInDegress = (float)Math.toDegrees(azimuthInRadians)+360)%360;

Answer 2

// This answer applies to Google Maps api v2.
// It is possible by registering your application with Sensor Listener for Orientation and get the
// angle relative to true north inside onSensorChanged and update camera accordingly.
// Angle can be used for bearing. Following code can be used:

// Instead of using Sensor.TYPE_ORIENTATION try using getOrinetation api. Sensor.TYPE_ORIENTATION
// has been deprecated.

@Override
protected 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 compassBearingRelativeToTrueNorth = Math.round(event.values[0]);

    Log.d(TAG, "Degree ---------- " + degree);

    updateCamera(compassBearingRelativeToTrueNorth);

}

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

    CameraPosition pos = CameraPosition.builder(oldPos).bearing(bearing)
            .build();

    googleMap.moveCamera(CameraUpdateFactory.newCameraPosition(pos));

}

Answer 3

The values are in radian, you have to convert to degree of arc

int azimut = (int) Math.round(Math.toDegrees(orientation[0]));