Develop Reference

Angle of phone rotated along X axis

I am working on an Android app wherein I want to scroll a large image horizontally. I used the accelerometer (Sensor.TYPE_ACCELEROMETER) and magnetic field (Sensor.TYPE_MAGNETIC_FIELD) data to get the angle of rotation. This data being to frequent infested with noise I am not able to implement a smooth motion effect.
#Override
public void onSensorChanged(SensorEvent event) {
switch (event.sensor.getType()) {
case Sensor.TYPE_MAGNETIC_FIELD:
mags = event.values.clone();
break;
case Sensor.TYPE_ACCELEROMETER:
accels = event.values.clone();
break;
}
if (mags != null && accels != null) {
gravity = new float[16];
boolean success = SensorManager.getRotationMatrix(gravity, null, accels, mags);
if (success) {
float[] outGravity = new float[16];
SensorManager.remapCoordinateSystem(gravity, SensorManager.AXIS_X, SensorManager.AXIS_Z, outGravity);
SensorManager.getOrientation(outGravity, values);
rollingAverage[0] = roll(rollingAverage[0], values[0]);
rollingAverage[1] = roll(rollingAverage[1], values[1]);
rollingAverage[2] = roll(rollingAverage[2], values[2]);
azimuth = Math.toDegrees(values[0]);
pitch = Math.toDegrees(values[1]);
roll = Math.toDegrees(values[2]);
mags = null;
accels = null;
double diffRoll = lastRoll - roll;
double diffPitch = lastPitch - pitch;
long curTime = System.currentTimeMillis();
if (Math.abs(diffRoll) >= 2) {
if (diffRoll > 0)
imageView.panLeft();
else
imageView.panRight();
lastRoll = roll;
}
}
}
}
Any ideas on achieving this using other methods?

You have to implement sensor fusion techniques based on Kalman filter or other filters. You can use open source libraries if needed. Refer this bitbucket repository. If you want to do yourself, read the tutorial.

For loop not acting as expected

Good night.
I have a for loop to calculate some values along the week, during some weeks. My code compare day of the week with the quantity of days that have passed.
The for only works fine on monday when workday is the same than totdays. The rest of days totact is 0 and the fianl equation become NaN.
int totdias = PrefProteos.getInt("dia",0);
int totact = 0;
float califtot = 0;
int stateday = 0;
float promdias;
float promcalif;
int workdays;
Date day = new Date();
SimpleDateFormat formatter = new SimpleDateFormat("EE", Locale.US);
String dayweek = formatter.format(day);
if (dayweek.equals("Mon")) {
stateday = 1;
}
else if (dayweek.equals("Tue")) {
stateday = 2;
}
else if (dayweek.equals("Wed")) {
stateday = 3;
}
else if (dayweek.equals("Thu")) {
stateday = 4;
}
else if (dayweek.equals("Fri")) {
stateday = 5;
}
else if (dayweek.equals("Sat")) {
stateday = 6;
}
else if (dayweek.equals("Sun")) {
stateday = 7;
}
if (stateday >= totdias) {
workdays = 1;
promdias = totdias;
} else {
workdays = (totdias - (stateday - 1));
promdias = stateday;
}
for (int y = workdays; y == totdias;y++) {
for (int x = 1; x <= 12; x++) {
String activ=PrefProteos.getString("act" + x + "-habit", "");
if (!activ.equals("")) {
float notactiv = PrefProteos.getFloat("act" + x + "-puntdia"+y, 0);
califtot = califtot+notactiv;
totact = totact+1;
}
}
}
promcalif = califtot / (totact * promdias);

You have write your first loop condition wrong, you ask only for to run only if workdays = totdias. I guess you want to loop for each days from workdays to totdias
So correct this block :
for (int y = workdays; y == totdias;y++) {
Into
for (int y = workdays; y <= totdias;y++) {
PS :
Your current loop is like writing
if(workdays == totdias) {

You should provide some more code because we can't understand your PrefProteos class and probably the error is in there.
You should also add the full logcat
And you should tell us which line throws the error.
Anyway there are some errors:
Here
for (int y = workdays;y==totdias;y++){
There is no sense of using an equals condition in a for loop exit condition if both equals condition and looping variable are the same, because it will result in an if loop. This is because the for will work only if workdays == totdias since the beginning, elseway it will not work.
For conditions are:
for(counter = defaultvalue; condition that if true, makes the loop goes on; what to do each loop end)
This means that your code will do:
is y(workdays) == totdias?
if yes, do the loop
add one to y(workdays)
exit because the condition is no more true
if not, don't run the loop
So you simply have to call:
if(y == totdias){
//do code
y++;
}
But probably this is an error, because except for monday, this code will never run! so in others days promdias is not istantiated
In the loop
for (int x = 1; x<=12; x++){
String activ=PrefProteos.getString("act" + x + "-habit", "");
if (!activ.equals("")){
//there must be an error here somewhere
float notactiv=PrefProteos.getFloat("act" + x + "-puntdia"+y, 0);
califtot=califtot+notactiv;
totact=totact+1;
}
}
And this must be throwing an error.
promcalif = califtot/(totact*promdias);
Two options:
promidias or totact are 0. you can't do number/0
As said above, promdias might not be istantiated in other days of the week, because the for loop never run
Btw, float name = 0; is not perfect, change them to float name = 0f;

creating a digital filter in android

I'm trying to deal with ECG signal processing in android. I want to implement simple digital filters (lowpass, highpass)
I've got a transfer function:
here is what i've found:
wikipedia - lowpass filter - it looks quite easy here.
for i from 1 to n
y[i] := y[i-1] + α * (x[i] - y[i-1])
but there is nothing about transfer function which I want to use.
I also found the following matlab code
%% Low Pass Filter H(z) = (1 - 2z^(-6) + z^(-12)) / (1 - 2z^(-1) + z^(-2))
b = [1 0 0 0 0 0 -2 0 0 0 0 0 1];
a = [1 -2 1];
h_l = filter(b,a,[1 zeros(1,12)]);
ecg_l = conv (ecg ,h_l);
but there is no function like filter and conv in java (or I missed something).
Also I was looking on stackoverflow for an answer. But I didn't found anything about transfer function.
so can someone help me? I just want to move on with my project.

Given a time-domain recurrence equation (such as the one you quoted from wikipedia), the corresponding transfer function in the z-domain can relatively easily be obtained by using the following properties:
Where X(z) and Y(z) are the z-transforms of the time-domain input sequence x and output sequence y respectively.
Going the other way around, given a transfer function which can be expressed as a ratio of polynomials in z, such as:
the recurrence equation of the transfer function can be written as:
There are of course many different ways to implement such a recurrence equation, but a simple filter implementation following the Direct Form II would be along the line of:
// Implementation of an Infinite Impulse Response (IIR) filter
// with recurrence equation:
// y[n] = -\sum_{i=1}^M a_i y[n-i] + \sum_{i=0}^N b_i x[n-i]
public class IIRFilter {
public IIRFilter(float a_[], float b_[]) {
// initialize memory elements
int N = Math.max(a_.length, b_.length);
memory = new float[N-1];
for (int i = 0; i < memory.length; i++) {
memory[i] = 0.0f;
}
// copy filter coefficients
a = new float[N];
int i = 0;
for (; i < a_.length; i++) {
a[i] = a_[i];
}
for (; i < N; i++) {
a[i] = 0.0f;
}
b = new float[N];
i = 0;
for (; i < b_.length; i++) {
b[i] = b_[i];
}
for (; i < N; i++) {
b[i] = 0.0f;
}
}
// Filter samples from input buffer, and store result in output buffer.
// Implementation based on Direct Form II.
// Works similar to matlab's "output = filter(b,a,input)" command
public void process(float input[], float output[]) {
for (int i = 0; i < input.length; i++) {
float in = input[i];
float out = 0.0f;
for (int j = memory.length-1; j >= 0; j--) {
in -= a[j+1] * memory[j];
out += b[j+1] * memory[j];
}
out += b[0] * in;
output[i] = out;
// shift memory
for (int j = memory.length-1; j > 0; j--) {
memory[j] = memory[j - 1];
}
memory[0] = in;
}
}
private float[] a;
private float[] b;
private float[] memory;
}
which you could use to implement your specific transfer function like so:
float g = 1.0f/32.0f; // overall filter gain
float[] a = {1, -2, 1};
float[] b = {g, 0, 0, 0, 0, 0, -2*g, 0, 0, 0, 0, 0, g};
IIRFilter filter = new IIRFilter(a, b);
filter.process(input, output);
Note that you can alternatively also factorize the numerator and denominator into 2nd order polynomials and obtain a cascade of 2nd order filters (known as biquad filters).

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);
}
}
}

updating Textview based on sensordata

I'm trying to update a textview based on sensorinput - more precise pitch. I have no problem getting the sensor data, converting it to degrees and displaying it in a textview.
The problem is, that I wan't different numbers displayed, based on the pitch in degrees. I have written a if-else if statement and placed it in the onsensorchanged, but apart from the initial number it does not update.
#Override
public void onSensorChanged(SensorEvent event) {
switch(event.sensor.getType()){
case Sensor.TYPE_ACCELEROMETER:
for(int i =0; i < 3; i++){
valuesAccelerometer[i] = event.values[i];
}
break;
case Sensor.TYPE_MAGNETIC_FIELD:
for(int i =0; i < 3; i++){
valuesMagneticField[i] = event.values[i];
}
break;
}
boolean success = SensorManager.getRotationMatrix(
matrixR,
matrixI,
valuesAccelerometer,
valuesMagneticField);
if(success){
SensorManager.getOrientation(matrixR, matrixValues);
// Float to double
double pitch = Math.toDegrees(matrixValues[1]);
// 1 decimal
pitch = Math.abs(round(pitch, 0));
//set textview vinkel to degrees
vinkel.setText(String.valueOf(pitch));
// find tubesize from edittext
String tubesizestring = tubesize.getText().toString();
if(tubesizestring=="1000"){
if(pitch>=0.6){
kwh.setText("2,69");
}else if(pitch>=1.0){
kwh.setText("3,47");
}else if(pitch>=2.0){
kwh.setText("4,90");
}else if(pitch>=5.0){
kwh.setText("7,75");
}else if(pitch>=10.0){
kwh.setText("10,96");
}else if(pitch>=20.0){
kwh.setText("15,50");
}else if(pitch>=30.0){
kwh.setText("18,99");
}else{
kwh.setText("more than 30 degrees");
}
}
}
I hope it is clear what I'm trying to do. Othervise please ask
Hope somebody can point me in the right direction

It doesn't work because your logic is fundamentally flawed. Let's assume the pitch is around 25. It's greater than 0.6 and 1.0 and so on. So obviously only the first if statement will be seen, since the others are else if statements. To get it to work, change the order of the statements.
if(pitch>=30.0){
kwh.setText("18,99");
}else if(pitch>=20.0){
kwh.setText("15,50");
}else if(pitch>=10.0){
kwh.setText("10,96");
}else if(pitch>=5.0){
kwh.setText("7,75");
}else if(pitch>=2.0){
kwh.setText("4,90");
}
else if(pitch>=1.0){
kwh.setText("3,47");
}
else if(pitch>=0.6){
kwh.setText("2,69");
}eelse{
kwh.setText("more than 30 degrees");