Orientation from Android Accelerometer

Question

I testing the accelerometer output on 2 different devices(Elocity A7 and Archos 7 Home tablet) but the sensor seems to be giving different results. I have it programmed to set to landscape mode but the x and y axis seem to be the oppisite between the 2 devices. The x axis returns 10 when held perpendicular to the ground and the Archos X axis returns 0. The Elocity tablet is android 2.2 and the Archos is 2.1. Can someone point me in the right direction as how to get orientation from the accelerometer in sync between these 2 devices?

Answer 1

In fact, the accelerometer axises are relative to the default orientation of the device.

Here how to deal with it:

static void canonicalOrientationToScreenOrientation(
         int displayRotation, float[] canVec, float[] screenVec) 
{ 
    final int axisSwap[][] = { 
    {  1,  -1,  0,  1  },     // ROTATION_0 
    {-1,  -1,  1,  0  },     // ROTATION_90 
    {-1,    1,  0,  1  },     // ROTATION_180 
    {  1,    1,  1,  0  }  }; // ROTATION_270 

    final int[] as = axisSwap[displayRotation]; 
    screenVec[0]  =  (float)as[0] * canVec[ as[2] ]; 
    screenVec[1]  =  (float)as[1] * canVec[ as[3] ]; 
    screenVec[2]  =  canVec[2]; 
} 

This solution was provided by NVidia. Check their white paper about Android Accelerometer for more details.

Answer 2

just wanted to add something to Hartok's answer as I couldn't understand it at first...

I've rewritten the method to be:

public static float[] adjustAccelOrientation(int displayRotation, float[] eventValues) 
{ 
    float[] adjustedValues = new float[3];

    final int axisSwap[][] = {
    {  1,  -1,  0,  1  },     // ROTATION_0 
    {-1,  -1,  1,  0  },     // ROTATION_90 
    {-1,    1,  0,  1  },     // ROTATION_180 
    {  1,    1,  1,  0  }  }; // ROTATION_270 

    final int[] as = axisSwap[displayRotation]; 
    adjustedValues[0]  =  (float)as[0] * eventValues[ as[2] ]; 
    adjustedValues[1]  =  (float)as[1] * eventValues[ as[3] ]; 
    adjustedValues[2]  =  eventValues[2];

    return adjustedValues;
}

Exactly the same thing, just with more user friendly variable names and I recreate the float internally because I needed it like that... Simply call this function, put in the getRotation and the event.values float array, check the values of its return float array and pick whatever number you prefer...

Hope this helps someone!