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Thread: Magnetic Sensor Droid X development issues

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    ocv808's Avatar
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    Jun 2011
    droid 1 and Nexus S

    Magnetic Sensor Droid X development issues

    Hello all,
    I have been trying to create a simple compass functionality in an application. I created the simple application doing testing on my Motorola droid 1 (2.22) and nexus S(2.34) and they seemed to work correctly (accuracy was not the best how-ever they work similar to other apps on the same phone so any differences i assumed to be hardware error).

    However i then tested the app on a droid X (2.33) and the results were completely different (and completely wrong). When the phone is rolled around 45 degrees (rotated around z axis a computer coordinate system) the compass heading returned can change over 180 degrees. The heading value even goes in the opposite direction of the other phones (nexus s and droid 1) when spun in the same direction. This is the only phone that produces this result even after calibrating in the settings and doing the normal figure 8 motion. Also when i test against another compass app on the droid x it doesnt seem to have the same issue, but my compass app on the other phones lines up with the 3rd party compass app. So I would assume there would be something i can do in software to avoid this but there is nothing i can find and most people say my code looks correct. Also what would be the difference between these phones to cause this do i have to have special cases for phones that have issues like this?

    Here is my code to perform the orientation calculations

    public void onSensorChanged(SensorEvent event)
            // If the sensor data is unreliable return
            if (event.accuracy == SensorManager.SENSOR_STATUS_UNRELIABLE)
                Toast.makeText(main.this, "Sensor Status Unreliable",Toast.LENGTH_SHORT).show();
            // Gets the value of the sensor that has been changed
            switch (event.sensor.getType())
            case Sensor.TYPE_ACCELEROMETER:
                m_vfgravity = event.values.clone();
            case Sensor.TYPE_MAGNETIC_FIELD:
                m_vfgeomag = event.values.clone();
            if (m_vfgravity != null && m_vfgeomag != null)
                if(SensorManager.getRotationMatrix(m_vfinR, m_vfI, m_vfgravity, m_vfgeomag))
                    SensorManager.getOrientation(m_vfinR, m_vforientVals);
                    m_fCompBearing = (float) Math.round((Math.toDegrees(m_vforientVals[0])) *2)/2;
                    //convert to 0-360 from -180-180
                    if(m_fCompBearing < 0.0)
                        m_fCompBearing = 360 + m_fCompBearing;
                    mCompHead.setText("" + (int)m_fCompBearing);

    and my initialization code

    mSMngr = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
        mSListener = new cSensorListener();
    Any insight and or advice would be greatly appreciated. This bug has been haunting me for almost a week now with no solution in sight. I still cant even identify the root of the problem.

    Thanks in advance !!


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