Android: Does getOrientation() require successive remaps?

Question

I have been trying to get heading values using the getOrientation() method.

boolean success = SensorManager.getRotationMatrix(rot, incl, accel, magnet);
if (success) {
    // Compute orientation
    float orientation[] = new float[3];
    SensorManager.getOrientation(rot, orientation);

}

These values vary wildly, even if I keep the phone steady and walk with it in a steady position.

I then tried to change the reference of my acceleration values from the phone to the world axis:

        // Compute world acceleration
        float wAccel[] = new float[4];
        float newAccel[] = new float[]{accel[0],accel[1],accel[2], 0};
        android.opengl.Matrix.multiplyMV(wAccel, 0, rot, 0, newAccel, 0);
        magnetLine += "W" + LOGSEPARATOR +
                tsString + LOGSEPARATOR +
                wAccel[0] + LOGSEPARATOR +
                wAccel[1] + LOGSEPARATOR +
                wAccel[2] + "\n";
    }

I then used values from the X and Y axis on an atan2 function to determine the angle of the vector. Even if varying in a different manner, these values still display strange behavior (sometimes the value is constant, other times it displays a periodical behavior, as if following the footsteps).

I have seen some instances of people calling remapCoordinate system for situations somewhat similar to this. Is this what I am missing?

score 1 · Accepted Answer · edited May 23 '17 at 11:50

Here's a couple of things that you could do:

First, unless you're working with older versions of the Android API, use Sensor.TYPE_GRAVITY instead of Sensor.TYPE_ACCELEROMETER. Sensor.TYPE_GRAVITY is meant to try and filter out movements, and just leave you with the gravity vector.
Monitor the accuracy of your sensors using the onAccuracyChanged(Sensor sensor, int accuracy) method of the SensorEventListener interface. I've had the same problem, and in my case it was happening when Sensor.TYPE_MAGNETIC_FIELD was becoming SensorManager.SENSOR_STATUS_UNRELIABLE.

The remapCoordinateSystem() is to do with making 90 degree rotations in your co-ordinate system, e.g. swapping the x with z axis etc. If you were e.g. making a compass which displayed the direction of true north, then you'd need that to take account of whether your device was in portrait or landscape mode etc. However, the measurements from the sensors don't depend on portrait/landscape, so if they're varying wildly then your problem lies elsewhere.

Also note android compass seems unreliable , some people have found that the compass in Android devices isn't very good. However, that post was about 2 years ago, so hopefully things are better now :-).

Thanks for the tip of using gravity sensors, that smoothed the signal out quite significantly. I don't think that I am losing magnetometer values in my graphs, because all these points are plotted whenever I get a reading. — ravemir, Apr 22 '13 at 11:29

Android: Does getOrientation() require successive remaps?

1 Answers1