How to read Android accelerometer values in a stable and accurate way?
Old question, but I'm answering here for the sake of others that find this question.
First off, following @andrew-morton link is exactly what I needed, but was in pseudo code, so here is Java for Android!
Second: If you can (you're min API Lvl is 9 or higher), simply use the Sensor.TYPE_GRAVITY. As it is already smoothed out. If you need to support older API Lvls (like I had to), this code should do the trick!
Lastly: This code snippet is somewhat modified from what I am using it for, if you want to use this for yourself, you'll need to create a getter for the Vector3 gravity.
Notes: I've found that a rolling average of 5 (MAX_SAMPLE_SIZE) is quite smooth. 10 is even more smooth, but you start to notice lag.
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import java.util.ArrayList;
import java.util.List;
/**
* Created by andy on 6/14/14.
*/
public class AndroidGravityUpdate implements SensorEventListener {
private SensorManager sensorManager;
Vector3 gravity;
List<Float>[] rollingAverage = new List[3];
private static final int MAX_SAMPLE_SIZE = 5;
AndroidGravityUpdate( SensorManager sensorManager ) {
this.gravity = new Vector3();
this.sensorManager = sensorManager;
if(sensorManager.getSensorList(Sensor.TYPE_GRAVITY).size() > 0){
sensorManager.registerListener(
this,
sensorManager.getDefaultSensor(Sensor.TYPE_GRAVITY),
SensorManager.SENSOR_DELAY_GAME
);
} else if( sensorManager.getSensorList(Sensor.TYPE_ACCELEROMETER).size() > 0) {
rollingAverage[0] = new ArrayList<Float>();
rollingAverage[1] = new ArrayList<Float>();
rollingAverage[2] = new ArrayList<Float>();
sensorManager.registerListener(
this,
sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),
SensorManager.SENSOR_DELAY_GAME
);
}
}
@Override
public void onSensorChanged(SensorEvent event) {
if (event.sensor.getType()==Sensor.TYPE_GRAVITY){
gravity.z = event.values[0];
gravity.x = event.values[1];
gravity.y = - event.values[2];
}
else if ( event.sensor.getType()==Sensor.TYPE_ACCELEROMETER) {
//For whatever reason, my Samsung only has "Accelerometer"
// But it is incredibly rough, so attempting to smooth
// it out with rolling averages.
rollingAverage[0] = roll(rollingAverage[0], event.values[0]);
rollingAverage[1] = roll(rollingAverage[1], event.values[1]);
rollingAverage[2] = roll(rollingAverage[2], -event.values[2]);
gravity.z = averageList(rollingAverage[0]);
gravity.x = averageList(rollingAverage[1]);
gravity.y = averageList(rollingAverage[2]);
}
}
public List<Float> roll(List<Float> list, float newMember){
if(list.size() == MAX_SAMPLE_SIZE){
list.remove(0);
}
list.add(newMember);
return list;
}
public float averageList(List<Float> tallyUp){
float total=0;
for(float item : tallyUp ){
total+=item;
}
total = total/tallyUp.size();
return total;
}
@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
}
}
class Vector3 {
float x;
float y;
float z;
}
Sachindra
Updated on June 04, 2022Comments
-
Sachindra about 2 years
In a my project I am trying to control a car using data obtained through the accelerometer of an Android device. (Left, Right, Forward, Reverse). Even though I have managed to read values from the accelerometer the readings are subject to frequent changes even the device is in a stable position. Can someone provide me a better way to do this?
Following is the code that I have used
import android.content.Context; import android.hardware.Sensor; import android.hardware.SensorEvent; import android.hardware.SensorEventListener; import android.hardware.SensorManager; public class AccelerometerService { private static SensorManager sensorManager; private static SensorEventListener sensorEventListener; private static boolean started = false; private static float[] accelerometer = new float[3]; private static float[] magneticField = new float[3]; private static float[] rotationMatrix = new float[9]; private static float[] inclinationMatrix = new float[9]; private static float[] attitude = new float[3]; private final static double RAD2DEG = 180/Math.PI; private static int initialAzimuth = 0; private static int initialPitch = 0; private static int initialRoll = 0; private static int[] attitudeInDegrees = new int[3]; public static void start(final Context applicationContext) { if(started) { return; } sensorManager = (SensorManager) applicationContext .getSystemService(Context.SENSOR_SERVICE); sensorEventListener = new SensorEventListener() { @Override public void onSensorChanged(SensorEvent event) { int type = event.sensor.getType(); if(type == Sensor.TYPE_MAGNETIC_FIELD) { magneticField = event.values.clone(); } if(type == Sensor.TYPE_ACCELEROMETER) { accelerometer = event.values.clone(); } SensorManager.getRotationMatrix(rotationMatrix, inclinationMatrix, accelerometer, magneticField); SensorManager.getOrientation(rotationMatrix, attitude); attitudeInDegrees[0] = (int) Math.round(attitude[0] * RAD2DEG); //azimuth attitudeInDegrees[1] = (int) Math.round(attitude[1] * RAD2DEG); //pitch attitudeInDegrees[2] = (int) Math.round(attitude[2] * RAD2DEG); //roll } @Override public void onAccuracyChanged(Sensor sensor, int accuracy) { } }; sensorManager.registerListener(sensorEventListener, sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER), SensorManager.SENSOR_DELAY_UI); sensorManager.registerListener(sensorEventListener, sensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD), SensorManager.SENSOR_DELAY_UI); started = true; } public static boolean getStarted() { return started; } public static void stop() { if(started) { sensorManager.unregisterListener(sensorEventListener); started = false; } } }