How to get accurate direction in phonegap?

Question

I developed a hybrid app using phonegap.

Using compass function in phonegap api and native code.

There is a problem.

My test devices (Galaxy Note 1, GalaxyS3, etc...) are not indicate same direction.

my phonegap source is...

document.addEventListener("deviceready", onDeviceReady, false);
function onDeviceReady() {
        startWatch();
    }

function startWatch() {

        // Update compass every 3 seconds
        var options = { frequency: 1000 };

        watchID = navigator.compass.watchHeading(onSuccess, onError, options);
    }

function onSuccess(heading) {
        var element = document.getElementById('heading');
        var deg = heading.magneticHeading;
        element.innerHTML = 'Heading: ' + deg + '<br>';        
    }

Reference phonegap api.

my native source is...

float[] mGravity;
float[] mGeomagnetic;

public void onSensorChanged(SensorEvent event) {
    if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER)
        mGravity = event.values.clone();
    if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD)
        mGeomagnetic = event.values.clone();
    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);
            azimut = (float)Math.toDegrees(orientation[0]);

            //for (-180 to 180), (-10 to 350) 
            if(azimut<0)
                azimut = azimut+360;                            Log.d("azimut",""+azimut);

            // orientation contains: azimut, pitch and roll
            Matrix matrix=new Matrix();
            imgView.setScaleType(ScaleType.MATRIX);   //required
            matrix.postRotate(360-azimut+angle, imgView.getWidth()/2,     imgView.getHeight()/2);
            imgView.setImageMatrix(matrix);

        }
    }
}

Reference google developer.

Why my devices can't indicate same direction?

Answer 1

Considering in your comments you state it is your compass and not your code, the answer is to recalibrate your compass. Please see linked instructions: http://forum.xda-developers.com/showthread.php?t=1778131