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How to sum of arrays of floating point numbers

How to sum of arrays of floating point numbers..as the results from distance that the array float come from results Location.distanceBetween(latStart, longStart, latB, longB, results); method in Google maps api ,,i'm trying with this, but at some point it decrease, it should always incrementing. what am i missing?
EDIT:
public float total(ArrayList<LatLng> listPoints){
if(listPoints.size()==2){
listPoints.clear();
}
listPoints.add(latLng);
float[] results = new float[2];
float sum = 0.0f;
for (int z = 0; z < listPoints.size(); z++) {
if(listPoints.size() == 1){
latStart = listPoints.get(z).latitude;
longStart = listPoints.get(z).longitude;
Toast.makeText(this, "listPoint 1", Toast.LENGTH_SHORT).show();
}else if(listPoints.size() == 2){
latB = listPoints.get(z).latitude;
longB = listPoints.get(z).longitude;
Toast.makeText(this, "listPoint 2", Toast.LENGTH_SHORT).show();
}
Location.distanceBetween(latStart, longStart, latB, longB, results);
sum+=results[0];
}
tvJarakTotal.setText(sum + "");
return sum;
}
EDIT:
the distance came from onLocationChanged() method as the user location is moving,
EDIT:
I Finally find the solution myself, by creating some trick using sharedPreference. but the accepted answer is correct to the question.

It is not entirely clear what you think you were doing in your code above. First of all, the Location#distanceBetween API takes in a pair of latitude longitude values, i.e. two geographic points, and then returns the distance between them in results[0] (q.v. the documentation).
Next, it isn't clear what the starting and ending points are intended to be. I answered below under the assumption that the listPoints are one set of points (either starting or ending), and the vales latB and longB are a fixed set of starting/ending points. Without this assumption, an answer really can't be given here.
public float total(ArrayList<LatLng> listPoints) {
float[] results;
float sum = 0.0f;
for (int z=0; z < listPoints.size(); z++) {
double latStart = listPoints.get(z).latitude;
double longStart = listPoints.get(z).longitude;
Location.distanceBetween(latStart, longStart, latB, longB, results);
sum += results[0];
tvJarak.setText(sum + "");
}
return sum;
}

Please take a look your code carefully.
float[] results = new float[listPoints.size()];
results variable is declared as a local variable but it's not initialized with any values yet.
In this case it has random value.
That's why sum gives random minus value.

float[] results = new float[listPoints.size()];
In this case your result array stored size of the listPoints array. After that you are trying to iterate result array by using listPointers array size.
Assume your :- float [] results = new [2];
Now you try to add up same value again and again inside you for a loop. Please make sure your scenario is correct or not.
You should store api date someware inside your code. like this:
lat = listPoints.get(z).latitude;
long = listPoints.get(z).longitude;
if you want you can do it like this,
public float total(ArrayList<LatLng> listPoints) {
float[] results;
float sum = 0.0f;
float lat = 0.0f, long = 0.0f;
for (int z=0; z < listPoints.size(); z++) {
lat = listPoints.get(z).latitude;
long = listPoints.get(z).longitude;
Location.distanceBetween(lat, long, latB, longB, results);
sum+=results[z];
tvJarak.setText(sum + "");
}
return sum;
}

how to calculate exact foot step count using accelerometer in android?

I am developing some application like Runtastic Pedometer using the algorithm but I am not getting any similarity between the results.
my code is as follows:
public void onSensorChanged(SensorEvent event)
{
Sensor sensor = event.sensor;
synchronized (this)
{
if (sensor.getType() == Sensor.TYPE_ORIENTATION) {}
else {
int j = (sensor.getType() == Sensor.TYPE_ACCELEROMETER) ? 1 : 0;
if (j == 1) {
float vSum = 0;
for (int i=0 ; i<3 ; i++) {
final float v = mYOffset + event.values[i] * mScale[j];
vSum += v;
}
int k = 0;
float v = vSum / 3;
//Log.e("data", "data"+v);
float direction = (v > mLastValues[k] ? 1 : (v < mLastValues[k] ? -1 : 0));
if (direction == - mLastDirections[k]) {
// Direction changed
int extType = (direction > 0 ? 0 : 1); // minumum or maximum?
mLastExtremes[extType][k] = mLastValues[k];
float diff = Math.abs(mLastExtremes[extType][k] - mLastExtremes[1 - extType][k]);
if (diff > mLimit) {
boolean isAlmostAsLargeAsPrevious = diff > (mLastDiff[k]*2/3);
boolean isPreviousLargeEnough = mLastDiff[k] > (diff/3);
boolean isNotContra = (mLastMatch != 1 - extType);
if (isAlmostAsLargeAsPrevious && isPreviousLargeEnough && isNotContra) {
for (StepListener stepListener : mStepListeners) {
stepListener.onStep();
}
mLastMatch = extType;
}
else {
Log.i(TAG, "no step");
mLastMatch = -1;
}
}
mLastDiff[k] = diff;
}
mLastDirections[k] = direction;
mLastValues[k] = v;
}
}
}
}
for registering sensors:
mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
mSensor = mSensorManager.getDefaultSensor(
Sensor.TYPE_ACCELEROMETER);
mSensorManager.registerListener(mStepDetector,mSensor,SensorManager.SENSOR_DELAY_NORMAL);
in the algorithm i have different levels for sensitivity as public void
setSensitivity(float sensitivity) {
mLimit = sensitivity; // 1.97 2.96 4.44 6.66 10.00 15.00 22.50 33.75 50.62
}
on various sensitivity level my result is:
sensitivity rantastic pedometer my app
10.00 3870 5500
11.00 3000 4000
11.15 3765 4576
13.00 2000 890
11.30 754 986
I am not getting any proper pattern to match with the requirement.
As per my analysis this application is using Sensor.TYPE_MAGNETIC_FIELD for steps calculation please let me know some algorithm so that I can meet with the requirement.

The first thing you need to do is decide on an algorithm. As far as I know there are roughly speaking three ways to detect steps using accelerometers that are described in the literature:
Use the Pythagorean theorem to calculate the magnitude of the acceleration vector of each sample from the accelerometer. Low-pass filter the magnitude signal to remove high frequency noise and then look for peaks and valleys in the filtered signal. You may need to add additional requirements to remove false positives. This is by far the simplest way to detect steps, it is also the way that most if not all ordinary pedometers of the sort that you can buy from a sports store work.
Use Pythagoras' like in (1), then run the signal through an FFT and compare the output from the FFT to known outputs of walking. This requires you to have access to a fairly large amount of training data.
Feed the accelerometer data into an algorithm that uses some suitable machine learning technique, for example a neural network or a digital wavelet transform. You can of course include other sensors in this approach. This also requires you to have access to a fairly large amount of training data.
Once you have decided on an algorithm you will probably want to use something like Matlab or SciPy to test your algorithm on your computer using recordings that you have made on Android phones. Dump accelerometer data to a cvs file on your phone, make a record of how many steps the file represents, copy the file to your computer and run your algorithm on the data to see if it gets the step count right. That way you can detect problems with the algorithm and correct them.
If this sounds difficult, then the best way to get access to good step detection is probably to wait until more phones come with the built-in step counter that KitKat enables.

https://github.com/bagilevi/android-pedometer
i hope this might be helpfull

I am using step detection in my walking instrument.
I get nice results of step detection.
I use achartengine to plot accelerometer data.
Take a look here.
What I do:
Analysis of magnitude vector for accelerometer sensor.
Setting a changeable threshold level. When signal from accelerometer is above it I count it as a step.
Setting the time of inactive state (for step detection) after first crossing of the threshold.
Point 3. is calculated:
arbitrary setting the maximum tempo of our walking (e.g. 120bpm)
if 60bpm - 1000msec per step, then 120bpm - 500msec per step
accelerometer passes data with certain desired frequency (SENSOR_DELAY_NORMAL, SENSOR_DELAY_GAME, etc.). When DELAY_GAME: T ~= 20ms (this is included in Android documentation)
n - samples to omit (after passing the threshold)
n = 500msec / T
n = 500 / 20 = 25 (plenty of them. You can adjust this value).
after that, the threshold becomes active.
Take a look at this picture:

This is my realization. It was written about 1.5-2 years ago. And I really don't remember all this stuff that I wrote. But it worked. And it worked good for my needs.
I know that this is really big class (some methods are deleted), but may be it will be helpful. If not, I'll just remove this answer...
public class StepDetector implements SensorEventListener
{
public static final int MAX_BUFFER_SIZE = 5;
private static final int Y_DATA_COUNT = 4;
private static final double MIN_GRAVITY = 2;
private static final double MAX_GRAVITY = 1200;
public void onSensorChanged(final SensorEvent sensorEvent)
{
final float[] values = sensorEvent.values;
final Sensor sensor = sensorEvent.sensor;
if (sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD)
{
magneticDetector(values, sensorEvent.timestamp / (500 * 10 ^ 6l));
}
if (sensor.getType() == Sensor.TYPE_ACCELEROMETER)
{
accelDetector(values, sensorEvent.timestamp / (500 * 10 ^ 6l));
}
}
private ArrayList<float[]> mAccelDataBuffer = new ArrayList<float[]>();
private ArrayList<Long> mMagneticFireData = new ArrayList<Long>();
private Long mLastStepTime = null;
private ArrayList<Pair> mAccelFireData = new ArrayList<Pair>();
private void accelDetector(float[] detectedValues, long timeStamp)
{
float[] currentValues = new float[3];
for (int i = 0; i < currentValues.length; ++i)
{
currentValues[i] = detectedValues[i];
}
mAccelDataBuffer.add(currentValues);
if (mAccelDataBuffer.size() > StepDetector.MAX_BUFFER_SIZE)
{
double avgGravity = 0;
for (float[] values : mAccelDataBuffer)
{
avgGravity += Math.abs(Math.sqrt(
values[0] * values[0] + values[1] * values[1] + values[2] * values[2]) - SensorManager.STANDARD_GRAVITY);
}
avgGravity /= mAccelDataBuffer.size();
if (avgGravity >= MIN_GRAVITY && avgGravity < MAX_GRAVITY)
{
mAccelFireData.add(new Pair(timeStamp, true));
}
else
{
mAccelFireData.add(new Pair(timeStamp, false));
}
if (mAccelFireData.size() >= Y_DATA_COUNT)
{
checkData(mAccelFireData, timeStamp);
mAccelFireData.remove(0);
}
mAccelDataBuffer.clear();
}
}
private void checkData(ArrayList<Pair> accelFireData, long timeStamp)
{
boolean stepAlreadyDetected = false;
Iterator<Pair> iterator = accelFireData.iterator();
while (iterator.hasNext() && !stepAlreadyDetected)
{
stepAlreadyDetected = iterator.next().first.equals(mLastStepTime);
}
if (!stepAlreadyDetected)
{
int firstPosition = Collections.binarySearch(mMagneticFireData, accelFireData.get(0).first);
int secondPosition = Collections
.binarySearch(mMagneticFireData, accelFireData.get(accelFireData.size() - 1).first - 1);
if (firstPosition > 0 || secondPosition > 0 || firstPosition != secondPosition)
{
if (firstPosition < 0)
{
firstPosition = -firstPosition - 1;
}
if (firstPosition < mMagneticFireData.size() && firstPosition > 0)
{
mMagneticFireData = new ArrayList<Long>(
mMagneticFireData.subList(firstPosition - 1, mMagneticFireData.size()));
}
iterator = accelFireData.iterator();
while (iterator.hasNext())
{
if (iterator.next().second)
{
mLastStepTime = timeStamp;
accelFireData.remove(accelFireData.size() - 1);
accelFireData.add(new Pair(timeStamp, false));
onStep();
break;
}
}
}
}
}
private float mLastDirections;
private float mLastValues;
private float mLastExtremes[] = new float[2];
private Integer mLastType;
private ArrayList<Float> mMagneticDataBuffer = new ArrayList<Float>();
private void magneticDetector(float[] values, long timeStamp)
{
mMagneticDataBuffer.add(values[2]);
if (mMagneticDataBuffer.size() > StepDetector.MAX_BUFFER_SIZE)
{
float avg = 0;
for (int i = 0; i < mMagneticDataBuffer.size(); ++i)
{
avg += mMagneticDataBuffer.get(i);
}
avg /= mMagneticDataBuffer.size();
float direction = (avg > mLastValues ? 1 : (avg < mLastValues ? -1 : 0));
if (direction == -mLastDirections)
{
// Direction changed
int extType = (direction > 0 ? 0 : 1); // minumum or maximum?
mLastExtremes[extType] = mLastValues;
float diff = Math.abs(mLastExtremes[extType] - mLastExtremes[1 - extType]);
if (diff > 8 && (null == mLastType || mLastType != extType))
{
mLastType = extType;
mMagneticFireData.add(timeStamp);
}
}
mLastDirections = direction;
mLastValues = avg;
mMagneticDataBuffer.clear();
}
}
public static class Pair implements Serializable
{
Long first;
boolean second;
public Pair(long first, boolean second)
{
this.first = first;
this.second = second;
}
#Override
public boolean equals(Object o)
{
if (o instanceof Pair)
{
return first.equals(((Pair) o).first);
}
return false;
}
}
}

One main difference I spotted between your implementation and the code in the grepcode project is the way you register the listener.
Your code:
mSensorManager.registerListener(mStepDetector,
mSensor,
SensorManager.SENSOR_DELAY_NORMAL);
Their code:
mSensorManager.registerListener(mStepDetector,
mSensor,
SensorManager.SENSOR_DELAY_FASTEST);
This is a big difference. SENSOR_DELAY_NORMAL is intended for orientation changes, and is therefor not that fast (ever noticed that it takes some time between you rotating the device, and the device actually rotating? That's because this is some functionality that does not need to be super fast (that would probably be pretty annoying even). The rate at which you get updates is not that high).
On the other hand, SENSOR_DELAY_FASTEST is intended for things like pedometers: you want the sensor data as fast and often as possible, so your calculations of steps will be as accurate as possible.
Try to switch to the SENSOR_DELAY_FASTEST rate, and test again! It should make a big difference.

public void onSensorChanged(SensorEvent event) {
if (event.sensor.getType()==Sensor.TYPE_ACCELEROMETER ){
float x = event.values[0];
float y = event.values[1];
float z = event.values[2];
currentvectorSum = (x*x + y*y + z*z);
if(currentvectorSum < 100 && inStep==false){
inStep = true;
}
if(currentvectorSum > 125 && inStep==true){
inStep = false;
numSteps++;
Log.d("TAG_ACCELEROMETER", "\t" + numSteps);
}
}
}

Is that possible Accelerometer 1hz update frequency?

is that possible to slow the the accelerometer update frequenzy to 1hz and how?
i've tried it on nexus 7 tab with this: changed the sensorDelay_Normal to 1.000.000 but nothing changed.
Thank You!
here is the code:
mAccelerometer.registerListener(listener,mAccelerometer.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),SensorManager.1000000);

This is how I get 1Hz acceleration:
static int ACCE_FILTER_DATA_MIN_TIME = 1000; // 1000ms
long lastSaved = System.currentTimeMillis();
#Override
public void onSensorChanged(SensorEvent event) {
if ((System.currentTimeMillis() - lastSaved) > ACCE_FILTER_DATA_MIN_TIME) {
lastSaved = System.currentTimeMillis();
float x = event.values[0];
float y = event.values[1];
float z = event.values[2];
}
}

You can always disregard measurements except one each second. Or do you want to spare battery?

okay i have found the solution:
public static final double accFreq = 15; //15 = 1 sec
long nowA = 0;
long timeA = 0;
int tempA = 0;
public SensorEventListener listener = new SensorEventListener() {
long tSA;
public void onSensorChanged(SensorEvent event) {
if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
float x = event.values[0];
float y = event.values[1];
float z = event.values[2];
// Get timestamp of the event
tSA = event.timestamp;
if (nowA != 0) {
tempA++;
if (tempA == settings.accFreq) {
timeA = tSA - nowA;
tempA = 0;
Log.e("Accelerometer:", "" + x + " " + y + " " + z);
}
}
if (tempA == 0) {
nowA = tSA;
}
}
}
This is the only way i can get it to work in 1Hz!

A custom value for the value of the sensor speed dont work well.
If you take a look into the class you will find the "getDelay" function in every .registerListener() methode.
public boolean registerListener(SensorEventListener listener, Sensor sensor, int rateUs,
int maxBatchReportLatencyUs) {
int delay = getDelay(rateUs);
return registerListenerImpl(listener, sensor, delay, null,maxBatchReportLatencyUs, 0);
}
Wich is also defined in the same class:
private static int getDelay(int rate) {
int delay = -1;
switch (rate) {
case SENSOR_DELAY_FASTEST:
delay = 0;
break;
case SENSOR_DELAY_GAME:
delay = 20000;
break;
case SENSOR_DELAY_UI:
delay = 66667;
break;
case SENSOR_DELAY_NORMAL:
delay = 200000;
break;
default:
delay = rate;
break;
}
return delay;
}
So normaly it should work to set a custom value.
But if you try to use custom values above about 100 milliseconds (100000 microseconds) the measured time between the events can jump up to 1000 milliseconds and stay there. If you go for 1000 ,2000 or much higher milliseconds the time between the events still are around 1000 milliseconds.
You can use SENSOR_DELAY_NORMAL (= 200 milliseconds) and catch the event if enough time passed by checking that every time (like David did)
If you go higher you should not use this enery draining approach - instead register the sensorListener catch the value and unregister it every time.

With the current approach the application is still getting events every 60ms. Just because it discards 14 out of 15 events, does NOT reduce the battery consumption as the sensor hardware still needs to process data once every 60ms and the system receives it and sends it to the application. i.e NOT much battery savings.
(nitpick alert) To be accurate with the above method, one needs to pick a sample from 16 or 17 events as each event occurs at around 60ms on an average.
The device freezing upon registering multiple sensorEventListeners at SENSOR_DELAY_NORMAL is NOT an issue with the Android framework (which can easily handle the scenario). This indicates an issue with how the application is written. The first thing to look for is a lot of cpu-intensive code within the main UI-thread. Follow the developer guidelines to make the application responsive with multiple sensorEventListeners() registered with SENSOR_DELAY_NORMAL and multiple worker threads performing the cpu-intensive calculations.

Android: Using the accelerometer to create a simple maraca app

I'm trying to learn how to use the accelerometer by creating (what I thought would be) a simple app to mimic a crude maraca.
The objective is that when the phone is flicked downwards quickly, it emits a maraca sound at the end of that flick, and likewise a different sound is emitted at the end of an upward flick.
The strategy for implementing this is to detect when the acceleration passes over a certain threshold. When this happens, ShakeIsHappening is set to true, and the data from the z axis is fed into an array. A comparison is made to see whether the first position in the z array is greater or lesser than the most recent position, to see whether the phone has been moved upwards or downwards. This is stored in a boolean called zup.
Once the acceleration goes below zero, we assume the flick movement has ended and emit a sound, chosen depending on whether the movement was up or down (zup).
Here is the code:
public class MainActivity extends Activity implements SensorEventListener {
private float mAccelNoGrav;
private float mAccelWithGrav;
private float mLastAccelWithGrav;
ArrayList<Float> z = new ArrayList<Float>();
public static float finalZ;
public static boolean shakeIsHappening;
public static int beatnumber = 0;
public static float highZ;
public static float lowZ;
public static boolean flick;
public static boolean pull;
public static SensorManager sensorManager;
public static Sensor accelerometer;
private SoundPool soundpool;
private HashMap<Integer, Integer> soundsMap;
private boolean zup;
private boolean shakeHasHappened;
public static int shakesound1 = 1;
public static int shakesound2 = 2;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
results = (TextView) findViewById(R.id.results);
clickresults = (TextView) findViewById(R.id.clickresults);
sensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
accelerometer = sensorManager
.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
mAccelNoGrav = 0.00f;
mAccelWithGrav = SensorManager.GRAVITY_EARTH;
mLastAccelWithGrav = SensorManager.GRAVITY_EARTH;
soundpool = new SoundPool(4, AudioManager.STREAM_MUSIC, 100);
soundsMap = new HashMap<Integer, Integer>();
soundsMap.put(shakesound1, soundpool.load(this, R.raw.shake1, 1));
soundsMap.put(shakesound2, soundpool.load(this, R.raw.shake1, 1));
}
public void playSound(int sound, float fSpeed) {
AudioManager mgr = (AudioManager)getSystemService(Context.AUDIO_SERVICE);
float streamVolumeCurrent = mgr.getStreamVolume(AudioManager.STREAM_MUSIC);
float streamVolumeMax = mgr.getStreamMaxVolume(AudioManager.STREAM_MUSIC);
float volume = streamVolumeCurrent / streamVolumeMax;
soundpool.play(soundsMap.get(sound), volume, volume, 1, 0, fSpeed);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
#Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
}
#Override
public void onSensorChanged(SensorEvent event) {
float x = event.values[0];
float y = event.values[1];
z.add((event.values[2])-SensorManager.GRAVITY_EARTH);
mLastAccelWithGrav = mAccelWithGrav;
mAccelWithGrav = android.util.FloatMath.sqrt(x * x + y * y + z.indexOf(z.size()-1) * z.indexOf(z.size()-1));
float delta = mAccelWithGrav - mLastAccelWithGrav;
mAccelNoGrav = mAccelNoGrav * 0.9f + delta; // Low-cut filter
if (mAccelNoGrav > 3) {
shakeIsHappening = true;
z.clear();
}
if (mAccelNoGrav < 0) {
if (shakeIsHappening) {
shakeIsHappening = false;
shakeHasHappened = true;
}
}
if (shakeIsHappening && z.size() != 0) {
if (z.get(z.size()-1) > z.get(0)) {
zup = true;
} else if (z.get(0) > z.get(z.size()-1)) {
zup = false;
}
}
if (shakeHasHappened) {
Log.d("click", "up is" + zup + "Low Z:" + z.get(0) + " high Z:" + z.get(z.size()-1));
if (!zup) {
shakeHasHappened = false;
playSound(shakesound2, 1.0f);
z.clear();
} else if (zup) {
shakeHasHappened = false;
playSound(shakesound1, 1.0f);
z.clear();
}
}
}
Some of the problems I'm having are:
I think ShakeHasHappened kicks in when deceleration starts, when acceleration goes below zero. Perhaps this should be when deceleration stops, when acceleration has gone negative and is now moving back towards zero. Does that sound sensible?
The way of detecting whether the motion is up or down isn't working - is this because I'm not getting an accurate reading of where the phone is when looking at the z axis because the acceleration is also included in the z-axis data and therefore isn't giving me an accurate position of the phone?
I'm getting lots of double clicks, and I can't quite work out why this is. Sometimes it doesn't click at all.
If anyone wants to have a play around with this code and see if they can find a way of making it more accurate and more efficient, please go ahead and share your findings. And if anyone can spot why it's not working the way I want it to, again please share your thoughts.
To link sounds to this code, drop your wav files into your res\raw folder and reference them in the R.raw.shake1 bit (no extension)
Thanks
EDIT: I've done a bit of research and have stumbled across something called Dynamic Time Warping. I don't know anything about this yet, but will start to look in to it. Does anyone know if DTW could be a different method of achieving a working maraca simulator app?

I can give you some pointers on this:
First of all, I noticed that you're using the same resource for both outcomes:
soundsMap.put(shakesound1, soundpool.load(this, R.raw.shake1, 1));
soundsMap.put(shakesound2, soundpool.load(this, R.raw.shake1, 1));
The resource in case of shakesound2 should be R.raw.shake2.
Second, the following only deals with one of the motions:
if (mAccelNoGrav > 3)
This should be changed to:
if (mAccelNoGrav > 3 || mAccelNoGrav < -3)
Currently, you are not intercepting downward motion.
Third, acceleration value of 3 is rather low. If you want to avoid/filter-out normal arm movement, this value should be around 6 or 7 and -6 or -7.
Fourth, you do not need to store z values to check whether the motion was up or down. You can check whether:
mAccelnoGrav > 6 ===> implies motion was upwards
mAccelnoGrav < -6 ===> implies motion was downwards
You can use this information to set zup accordingly.
Fifth: I can only guess that you are using if (mAccelNoGrav < 0) to play the sound when the motion ends. In that case, this check should be changed to:
if (mAccelNoGrav < epsilon || mAccelNoGrav > -epsilon)
where epsilon is some range such as (-1, 1).
Sixth, you should include a lockout period in your application. This would be the period after all conditions have been met and a sound is about to be played. For the next, say 1000 ms, don't process the sensor values. Let the motion stabilize. You'll need this to avoid getting multiple playbacks.
Note: Please include comments in your code. At the very least, place comments on every block of code to convey what you are trying to accomplish with it.

I tried to implement it by myself a time ago, and ended up using this solution.-
http://jarofgreen.co.uk/2013/02/android-shake-detection-library/
based on the same concept in your question.

using LinearAcceleration and time passed to get distance traveled - android [duplicate]

This question already has answers here:
How to use Accelerometer to measure distance for Android Application Development
(2 answers)
Closed 9 years ago.
I know i am opening up a can of worms with trying to get the linear motion of a device using the accelerometer, but please just humor me.
I am trying to figure out the right formula to take the Sensor.TYPE_LINEAR_ACCELEROMETER (which i believe is normal accelerometer data minus gravity) and essentially say "this much time has passed and the i have accelerated x amount since last time, so i have traveled d amount.
should be something like distanceTraveledOnX = linearAccerationOfX * TimePassed;
easy enough in the real world right? if i have been going 1 mile a minute for 10minutes then i have traveled 10 miles.. speed * time = distance
problem is im not sure what the linearAcceleration is using for unit of measure. I know my timePassed is in NanoSeconds as i am saying (in my onSensorChanged)
currentTime = System.nanoTime();//var of type (double)
timePassed = currentTime - lastTime;
lastTime = currentTime;
can someone please help me figure out the formula for translating the linearAcceleration value to a nanoSecond measurement..
thanks
EDIT
here is the code im currently using but im always getting 0 :
public void onSensorChanged(SensorEvent evt) {
if (type == Sensor.TYPE_LINEAR_ACCELERATION) {
newTime = System.currentTimeMillis()/1000;
float oldVelocity = lastTime1-lastTime0;
float newVelocity = newTime- lastTime1;
if(oldVelocity<1)oldVelocity =1;
newX = lastX1 + ((lastX1 - lastX0)/oldVelocity)*newVelocity +(evt.values[0]/2)*(newVelocity*newVelocity);
lastX0 = lastX1;
lastX1 = newX;
lastTime0 = lastTime1;
lastTime1 = newTime;
Log.v("SENSOR MAN LINEAR", "new X:"+newX);
}
}

This stuff is high school physics, and if you don't know the difference between acceleration and velocity, you'll need to review it before you have any hope here.
I can tell you this much: the linear acceleration readings from a cell phone or tablet aren't remotely precise or accurate enough to do what you want without constant correction (via gps or other methods). There is an entire field of study trying to solve this problem. I've attended conferences on it.
That said, you also need to take into account that the orientation of your device will also change, unless this is some sort of special application, e.g. the device is trapped onto a sled which can only move in one direction.
Let's assume that case, and assume that the device is strapped to your sled with the right side of the device (+X axis) aligned in the direction of travel. Let's also assume that the initial position of the sled is known (call it X0) when the program starts, and that the initial velocity is zero.
Your code looks approximately like this:
double x0; // previous position, meters
double x; // current position
double v0; // previous velocity, meters/second
double v; // current velocity
long t0; // previous time, nanoseconds
long t; // current time
public void onStart() {
x0 = getInitialPosition();
x = x0;
v0 = 0;
v = v;
t0 = System.getCurrentTime() * 1000000;
// Enable sensors; left as an exercise for the reader
}
public void onSensorChanged(SensorEvent event) {
// Assume linear acceleration is the only active sensor
double accel = event.values[0]; // X axis is our axis of acceleration
t = event.timestamp;
double dt = (t - t0) * .000001;
v = v0 + accel * dt;
x = x0 + v * dt;
t0 = t;
v0 = v;
x0 = x;
}
This is by no means a complete solution. Doing this right involves differential equations which I'm not equipped to explain here (translation: I've forgotten everything I learned in college). However, if your acceleration value is accurate enough, and your time slice is short enough, this is viable.
If you need to solve this in more than one direction, it's only slightly more complicated provided that the device never changes orientation. If it does, then you also need to capture the rotation sensor and learn about quaternions and rotation matrices.
And even if you do everything right, errors will still accumulate, so now you want some sort of correction factor based on GPS, known geometry of the environment (e.g. if you're indoors and the software has a map of the building, it can make corrections when you turn a corner), and other environmental clues such as WiFi hotspots in known locations.
You might want to read up on Kalman filters at this point.
Executive summary: this is a HARD problem in the general case, and if you solve it, there's probably fame and fortune waiting for you.

Well, the correct form, known from school, is
finalXPosition = (linearAcceleration*timePassed^2)/2+ initialVelocity*timePassed+initialXPosition
finalVelocity = initialVelocity*timePassed
chaining these chunks you'll get your theoretical values.
In practice, best results are achieved by regular calibration of initialXPosition and initialVelocity through GPS.
simple example to receive calibrated horizontal acceleration in onSensorChanged:
class Integrator {
private float position = 0f;
private float velocity = 0f;
public void setGpsPosition (float gpsPosition) {
position = gpsPosition;
}
public void setGpsVelocity (float gpsVelocity) {
velocity = gpsVelocity;
}
public void onAccelerationChangeHandler(float acceleration, float timePassed) {
position += acceleration*timePassed*timePassed/2f + velocity*timePassed;
velocity += acceleration*timePassed;
}
public float getCurrentPosition() {
return position;
}
}
usage for x-acceleration:
long lastTime = 0;
public void onSensorChanged(SensorEvent evt) {
if (evt.sensor.getType() == Sensor.TYPE_LINEAR_ACCELERATION) {
long newTime = System.currentTimeMillis();
OnAccelerationChangeHandler(evt.values[0], (newTime-lastTime)/1000);
lastTime = newTime;
}
Please, note that outside a minute scale the error makes this all meaningless w/o gps correction. Understand, that if you are walking at constant speed the sensor won't give you anything at all.