[android-developers] Android Compass help

Hi Guys,

             I need your help on developing an android compass application.Here is the source code...I want to know if i am using correct algorithm and sensors for developing the app and secondly I am unable to understand why my compass jitters so much

package com.android.compass.example

import android.app.Activity;

import android.hardware.Sensor;

import android.hardware.SensorEvent;

import android.hardware.SensorEventListener;

import android.hardware.SensorManager;

import android.os.Bundle;

public class CompassExample4Activity extends Activity implements SensorEventListener{

private SensorManager mSensorManager;

CompassView mCompassView;

Sensor accelerometer;

Sensor magnetometer;

float azimut;

float[] mGravity;

float[] mGeomagnetic;

static final float ALPHA = 0.2f;

double SmoothFactorCompass = 0.5;

double SmoothThresholdCompass = 30.0;

double oldCompass = 0.0;

int oldCompass2 = 0;

    /** Called when the activity is first created. */

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        mCompassView = new CompassView(this);

        //this.setRequestedOrientation(0);

        setContentView(mCompassView);

        

        mSensorManager = (SensorManager)getSystemService(SENSOR_SERVICE);

   accelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);

   magnetometer = mSensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);

    }

    

    @Override

    public void onResume() {

   super.onResume();

   mSensorManager.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_UI);

   mSensorManager.registerListener(this, magnetometer, SensorManager.SENSOR_DELAY_UI);

}

    @Override

public void onPause() {

   super.onPause();

   mSensorManager.unregisterListener(this);

}

 

@Override

public void onAccuracyChanged(Sensor sensor, int accuracy) {

// TODO Auto-generated method stub

}

@Override

public void onSensorChanged(SensorEvent event) {

// TODO Auto-generated method stub

if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER)

     mGravity = lowPass(event.values, mGravity);

if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD)

     mGeomagnetic = lowPass(event.values, mGeomagnetic);

   

if (mGravity != null && mGeomagnetic != null) {

     float R[] = new float[9];

     float I[] = new float[9];

     boolean success = SensorManager.getRotationMatrix(R, I, mGravity, mGeomagnetic);

     // Correct if screen is in Landscape

     SensorManager.remapCoordinateSystem(R, SensorManager.AXIS_X,

               SensorManager.AXIS_Z, R);

           

     if (success) {

       float orientation[] = new float[3];

       SensorManager.getOrientation(R, orientation);

       float azimut = orientation[0]; // orientation contains: azimut, pitch and roll

       //float azimuth = (float) Math.round((Math.toDegrees(orientation[0]))*7)/7;

       //azimuth = ( azimuth + 360)%360; 

       

       mCompassView.updateDirection((float)smoothnessFunction(azimut*360/(2*3.14159f)));

       //mCompassView.updateDirection(azimuth);

     }

}

}

protected float[] lowPass( float[] input, float[] output ) {

   if ( output == null ) return input;

   for ( int i=0; i<input.length; i++ ) {

       output[i] = output[i] + ALPHA * (input[i] - output[i]);

   }

   return output;

}

public double smoothnessFunction( double newCompass) {

if (Math.abs(newCompass - oldCompass) < 180) {

   if (Math.abs(newCompass - oldCompass) > SmoothThresholdCompass) {

       oldCompass = newCompass;

   }

   else {

       oldCompass = oldCompass + SmoothFactorCompass * (newCompass - oldCompass);

   }

} else {

   if (360.0 - Math.abs(newCompass - oldCompass) > SmoothThresholdCompass) {

       oldCompass = newCompass;

   } else {

       if (oldCompass > newCompass) {

           oldCompass = (oldCompass + SmoothFactorCompass * ((360 + newCompass - oldCompass) % 360) + 360) % 360;

       } else {

           oldCompass = (oldCompass - SmoothFactorCompass * ((360 - newCompass + oldCompass) % 360) + 360) % 360;

       }

   }

}

return oldCompass;

}

public int smoothnessFunction2(double newCompass){

if ((int)newCompass % 360 != oldCompass2) {

oldCompass2 = (int) newCompass;

}

return oldCompass2;

}

}

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