问题
I need suggestion about how to detect the amount of movement of an android device. Suppose I have put the phone on a table or bed and then if somebody taps the table or sits or laydown on the bed then I want to detect the movement of the android device.
Actually I know that android has motion sensors APIs but I don't know which sensor to use and what sensor type is best for this type of movement detection.
I would be glad if someone can share some basic demo code.
回答1:
Definitely work with the accelerometer:
// Start with some variables
private SensorManager sensorMan;
private Sensor accelerometer;
private float[] mGravity;
private float mAccel;
private float mAccelCurrent;
private float mAccelLast;
// In onCreate method
sensorMan = (SensorManager)getSystemService(SENSOR_SERVICE);
accelerometer = sensorMan.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
mAccel = 0.00f;
mAccelCurrent = SensorManager.GRAVITY_EARTH;
mAccelLast = SensorManager.GRAVITY_EARTH;
// And these:
@Override
public void onResume() {
super.onResume();
sensorMan.registerListener(this, accelerometer,
SensorManager.SENSOR_DELAY_UI);
}
@Override
protected void onPause() {
super.onPause();
sensorMan.unregisterListener(this);
}
@Override
public void onSensorChanged(SensorEvent event) {
if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER){
mGravity = event.values.clone();
// Shake detection
float x = mGravity[0];
float y = mGravity[1];
float z = mGravity[2];
mAccelLast = mAccelCurrent;
mAccelCurrent = FloatMath.sqrt(x*x + y*y + z*z);
float delta = mAccelCurrent - mAccelLast;
mAccel = mAccel * 0.9f + delta;
// Make this higher or lower according to how much
// motion you want to detect
if(mAccel > 3){
// do something
}
}
}
@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
// required method
}
回答2:
I used the following class:
public class MovementDetector implements SensorEventListener {
protected final String TAG = getClass().getSimpleName();
private SensorManager sensorMan;
private Sensor accelerometer;
private MovementDetector() {
}
private static MovementDetector mInstance;
public static MovementDetector getInstance() {
if (mInstance == null) {
mInstance = new MovementDetector();
mInstance.init();
}
return mInstance;
}
//////////////////////
private HashSet<Listener> mListeners = new HashSet<MovementDetector.Listener>();
private void init() {
sensorMan = (SensorManager) GlobalData.getInstance().getContext().getSystemService(Context.SENSOR_SERVICE);
accelerometer = sensorMan.getDefaultSensor(Sensor.TYPE_LINEAR_ACCELERATION);
}
public void start() {
sensorMan.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_NORMAL);
}
public void stop() {
sensorMan.unregisterListener(this);
}
public void addListener(Listener listener) {
mListeners.add(listener);
}
/* (non-Javadoc)
* @see android.hardware.SensorEventListener#onSensorChanged(android.hardware.SensorEvent)
*/
@Override
public void onSensorChanged(SensorEvent event) {
if (event.sensor.getType() == Sensor.TYPE_LINEAR_ACCELERATION) {
float x = event.values[0];
float y = event.values[1];
float z = event.values[2];
float diff = (float) Math.sqrt(x * x + y * y + z * z);
if (diff > 0.5) // 0.5 is a threshold, you can test it and change it
Log.d(TAG,"Device motion detected!!!!");
for (Listener listener : mListeners) {
listener.onMotionDetected(event, diff);
}
}
}
/* (non-Javadoc)
* @see android.hardware.SensorEventListener#onAccuracyChanged(android.hardware.Sensor, int)
*/
@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
// TODO Auto-generated method stub
}
public interface Listener {
void onMotionDetected(SensorEvent event, float acceleration);
}
}
Usage:
On my activity onCrate():
MovementDetector.getInstance().addListener(new MovementDetector.Listener() {
@Override
public void onMotionDetected(SensorEvent event, float acceleration) {
mMotionDetectionTextView.setText("Acceleration: ["+String.format("%.3f",event.values[0])+","+String.format("%.3f",event.values[1])+","+String.format("%.3f",event.values[2])+"] "+String.format("%.3f", acceleration));
if (acceleration > SettingsHelper.getInstance().getMotionDetectionThreshold()){
mMotionDetectionTextView.setTextColor(Color.RED);
} else {
mMotionDetectionTextView.setTextColor(Color.WHITE);
}
}
});
On my activity onResume():
MovementDetector.getInstance().start();
On my activity onPause():
MovementDetector.getInstance().stop();
回答3:
This code is for walking detection (Modified from @anthropomo code)
to get smoother value.
// initialize
private SensorManager sensorMan;
private Sensor accelerometer;
private float[] mGravity;
private double mAccel;
private double mAccelCurrent;
private double mAccelLast;
private boolean sensorRegistered = false;
// onCreate
sensorMan = (SensorManager) context.getSystemService(Context.SENSOR_SERVICE);
accelerometer = sensorMan.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
mAccel = 0.00f;
mAccelCurrent = SensorManager.GRAVITY_EARTH;
mAccelLast = SensorManager.GRAVITY_EARTH;
sensorMan.registerListener(this, accelerometer,
SensorManager.SENSOR_DELAY_NORMAL);
sensorRegistered = true;
// onSensorChanged
private int hitCount = 0;
private double hitSum = 0;
private double hitResult = 0;
private final int SAMPLE_SIZE = 50; // change this sample size as you want, higher is more precise but slow measure.
private final double THRESHOLD = 0.2; // change this threshold as you want, higher is more spike movement
@Override
public void onSensorChanged(SensorEvent event) {
if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
mGravity = event.values.clone();
// Shake detection
double x = mGravity[0];
double y = mGravity[1];
double z = mGravity[2];
mAccelLast = mAccelCurrent;
mAccelCurrent = Math.sqrt(x * x + y * y + z * z);
double delta = mAccelCurrent - mAccelLast;
mAccel = mAccel * 0.9f + delta;
if (hitCount <= SAMPLE_SIZE) {
hitCount++;
hitSum += Math.abs(mAccel);
} else {
hitResult = hitSum / SAMPLE_SIZE;
Log.d(TAG, String.valueOf(hitResult));
if (hitResult > THRESHOLD) {
Log.d(TAG, "Walking");
} else {
Log.d(TAG, "Stop Walking");
}
hitCount = 0;
hitSum = 0;
hitResult = 0;
}
}
}
回答4:
While I don't have demo code (since you aren't specific enough), a good start is here: http://developer.android.com/guide/topics/sensors/sensors_motion.html (and other items on the left).
回答5:
if you are trying to find the displacement of your phone, you need to find the Linear acceleration acting on your phone rather than the acceleration due to gravity
android has a built in converter to find the LINEAR ACCELERATION acting on your mobile phone
https://github.com/yuvaramsingh94/AndroidSensorTestCode/tree/master
this is a code where you can see how to get the raw value of LINEAR ACCELERATION
回答6:
I have been working with a similar idea to measure the displacement of the phone. I have found that the LINEAR ACCELERATION (and ACCELERATION) are not accurate enough to correctly measure the displacement.
This code should work a little better:
(ititialize)
private SensorManager sensorManager;
private Sensor accelerometer;
double[] maxAccelerations = new double[3];
double[] position = new double[3];
long[] times = new long[3];
// time combined with maxAcceleration can approximate the change in position,
// with the formula Δpos = (maxAcceleration * time ^ 2) / 6
long currentTime;
(onCreate)
sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
if (sensorManager.getDefaultSensor(Sensor.TYPE_LINEAR_ACCELERATION) != null) {
accelerometer = sensorManager.getDefaultSensor(Sensor.TYPE_LINEAR_ACCELERATION);
sensorManager.registerListener(this, accelerometer, sensorManager.SENSOR_DELAY_FASTEST);
}
currentTime = System.currentTimeMillis();
for(int i=0;i<3;i++){
times[i]=currentTime;
}
else{
throw "Error";
//Which will throw an error, if not the error that is expected. 😉
}
(onSensorChanged and onAccuracyChanged)
@Override
public void onAccuracyChanged(Sensor ignore, int thisFunction) {
}
@Override
public void onSensorChanged(SensorEvent event) {
if (event.sensor.getType() == Sensor.TYPE_LINEAR_ACCELERATION) {
for(int i=0;i<3;i++){
if(Math.abs(event.values[i])<0.01){
// Note: this is to try to prevent accelerating time from being counted when the phone is stationary. 0.01 should be
// changed to an appropriate sensitivity level that can be calculated by finding an average noise level when the phone is stationary.
times[i]=System.currentTimeMillis();
}
if(event.values[i]>maxAccelerations[i] && maxAccelerations[i]>=0){
maxAccelerations[i]=event.values[i];
}
else if(event.values[i]<maxAccelerations[i] && maxAccelerations[i]<=0){
maxAccelerations[i]=event.values[i];
}
else if(event.values[i]>0 && maxAccelerations[i]<0){
currentTime = System.currentTimeMillis();
position[i]+=maxAccelerations[i] * (times[i]-currentTime)*(times[i]-currentTime) / 6;
times[i]=currentTime;
maxAccelerations[i]=event.values[i];
}
else if(event.values[i]<0 && maxAccelerations[i]>0){
currentTime = System.currentTimeMillis();
position[i]+=maxAccelerations[i] * (times[i]-currentTime)*(times[i]-currentTime) / 6;
times[i]=currentTime;
maxAccelerations[i]=event.values[i];
}
}
}
}
来源：https://stackoverflow.com/questions/14574879/how-to-detect-movement-of-an-android-device