I am developing application for car acceleration tracking. I used standard accelerometer, calibrating it in specific position beforehand.

Then, assuming phone's orientation is not changing, I logged the accelerometer data for a specified time and calculated move parameters, one of which is the car's speed at the end of the test.

It works rather well, on a straight, horizontal road: error of a few percent.

But then I found out, that in API-level 10 there is a virtual sensor called TYPE_LINEAR_ACCELERATION and, as far as I understand, it must do what I need: filter gravity, orientation changes - so I may use it and get pure linear acceleration of mobile device.

BUT in real life..

I made a simple application, that does a little test:

//public class Accelerometer implements SensorEventListener { ...
public void onSensorChanged(SensorEvent se) 
{
    if(!active)
        return;

    lastX = se.values[SensorManager.DATA_X];
    lastY = se.values[SensorManager.DATA_Y];
    lastZ = se.values[SensorManager.DATA_Z];
    long now = System.currentTimeMillis();
    interval = now - lastEvetn;
    lastEvetn = now;
    out.write(Float.toString(lastX) + ";" + 
                    Float.toString(lastY) + ";" + 
                    Float.toString(lastZ) + ";" + 
                    Long.toString(interval) + "\n");
}

I bind a listener with the following parameters:

  mSensorManager.registerListener(linAcc,
                mSensorManager.getDefaultSensor(Sensor.TYPE_LINEAR_ACCELERATION),
                SensorManager.SENSOR_DELAY_GAME);

It works OK, but when I analyzed data dump, calculating speed like V = V0 + AT, where V0 = 0 at first, then - speed of interval before this, A = acceleration (SQRT (x*x+y*y+z*z)) (t = time of interval), eventually I get a very low speed - three times less than real speed.

Changing Sens

android accelerometer sensors
Edit
Report