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Editorial Team
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Asked: 2026-06-05T19:42:31+00:00

If I have a simple web page and script that looks like this: <body>

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If I have a simple web page and script that looks like this:

<body>
    <div id="alpha">a</div>
    <div id="beta">b</div>
    <div id="gamma">g</div>
</body>

<script>
window.addEventListener('deviceorientation', function(event) {
    var alpha = event.alpha;
    var beta = event.beta;
    var gamma = event.gamma;

    document.getElementById("alpha").innerHTML = alpha;
    document.getElementById("beta").innerHTML = beta;
    document.getElementById("gamma").innerHTML = gamma;

}, false);
</script>

I can open it up in mobile Firefox for Android and it will output 3 numbers that look like the following:

89.256125
3.109375
0.28125

Where when I rotate the device, the numbers change based on the axis of rotation. I noticed the values for “alpha” are really noisy – they bounce around non-stop even if the phone is at rest on my desk, while the other two remain steady. I understand that alpha is my heading. I’m curious then, is it getting the “alpha” value from the compass (which has noise issues) and the other two from the gyroscope?

Another issue is when I change the pitch, for some reason the heading changes too, even if I don’t actually change the heading. I’m just curious why this is and how it can be corrected?

Also, since the gyroscope measures angular velocity, I presume this event listener is integrating it automatically – is the integration algorithm as good as any? Does it use the accelerometer to correct the drift?

In this google tech talk video, from 15:00 to 19:00, the speaker talks about correcting the drift inherent in the gyroscope by using the accelermoter, as well as calibrating the orientation with respect to gravity: http://www.youtube.com/watch?v=C7JQ7Rpwn2k
How would I go about doing this?

Thanks for any insights anyone may have.

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1 Answer

  1. Editorial Team

    The device orientation is obtained by sensor fusion. Strictly speaking, none of the sensors measures it. The orientation is the result of merging the accelerometer, gyro and magnetometer data in a smart way.

    I noticed the values for “alpha” are really noisy – they bounce around
    non-stop even if the phone is at rest on my desk, while the other two
    remain steady.

    This a common problem with the Euler angles, try to avoid them if you can.

    By the way, the Sensor Fusion on Android Devices: A Revolution in Motion Processing video you link to explains it at 38:25.

    Also, since the gyroscope measures angular velocity, I presume this
    event listener is integrating it automatically – is the integration
    algorithm as good as any? Does it use the accelerometer to correct the
    drift?

    Yes, the gyro drift is corrected with the help of the accelerometer (and magnetometer, if any) readings. This is called sensor fusion.

    In this google tech talk video, from 15:00 to 19:00, the speaker talks
    about correcting the drift inherent in the gyroscope by using the
    accelermoter, as well as calibrating the orientation with respect to
    gravity: http://www.youtube.com/watch?v=C7JQ7Rpwn2k How would I go
    about doing this?

    If you have orientation then somebody already did all this for you. You don’t have to do anything.

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