Develop Reference

Android calculating Velocity wtih Accelerometer data

Due to the power consuming GPS data, I would like to calculate the device speed with only the accelerometer x,y and z data. I have read a lot of questions about this topic and I tried many set-ups to find a satisfactory solution to calculate the speed when my device is in my car.
It seems so simple but nothing works, which drives me crazy.
Been trying the Sensor.TYPE_LINEAR_ACCELERATION and the Sensor.TYPE_ACCELEROMETER with removed gravity. Tried a Low Pass Filter on the Linear acceleration data. Unfortunately all with no succes.
Looks like the calculated speed is correct but testing in my car the calculated speed doesn't get higher then about 2 m/s.
below a code snip
mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_LINEAR_ACCELERATION);
public void onSensorChanged(SensorEvent event) {
if (event.sensor == mAccelerometer) {
if (timestamp != 0) {
final float dT = (event.timestamp - timestamp) * NS2S;
lax = event.values[0];
lay = event.values[1];
laz = event.values[2];
vx = vxo + lax * dT ;
vy = vyo + lay * dT ;
vz = vzo + laz * dT ;
speed = (float) (Math.sqrt(vx*vx + vy*vy + vz*vz)) ;
if (speed < 0.01) {speed = 0 ; }
tv_speed.setText(String.valueOf(speed));
}
timestamp = event.timestamp;
}
}
Hope someone can help, thanks a lot.

It's possible to compute distance and speed using only accelerometer, but with three conditions:
1. Linear movement - trajectory must be straight.
2. Slope of the road must be constant.
3. You must perform calibration procedure before start.
Where can you use this method with such restrictions - it's up to you... Now, how to do it:
We need something, implementing SensorEventListener interface. For the future use, let's add following abstract class:
public abstract class Accelerometer implements SensorEventListener {
protected float lastX;
protected float lastY;
protected float lastZ;
public abstract Point getPoint();
public void onAccuracyChanged(Sensor arg0, int arg1) {
}
}
and this will be our SensorEventListener:
public class XYZAccelerometer extends Accelerometer {
private static final int BUFFER_SIZE = 500;
// calibration
private float dX = 0;
private float dY = 0;
private float dZ = 0;
// buffer variables
private float X;
private float Y;
private float Z;
private int cnt = 0;
// returns last SenorEvent parameters
public Point getLastPoint(){
return new Point(lastX, lastY, lastZ, 1);
}
// returrns parameters, using buffer: average acceleration
// since last call of getPoint().
public Point getPoint(){
if (cnt == 0){
return new Point(lastX, lastY, lastZ, 1);
}
Point p = new Point(X, Y, Z, cnt);
reset();
return p;
}
// resets buffer
public void reset(){
cnt = 0;
X = 0;
Y = 0;
Z = 0;
}
public void onSensorChanged(SensorEvent se) {
float x = se.values[SensorManager.DATA_X] + dX;
float y = se.values[SensorManager.DATA_Y] + dY;
float z = se.values[SensorManager.DATA_Z] + dZ;
lastX = x;
lastY = y;
lastZ = z;
X+= x;
Y+= y;
Z+= z;
if (cnt < BUFFER_SIZE-1) {
cnt++;
} else
{
reset();
}
}
public int getCnt(){
return cnt;
}
public void setdX(float dX) {
this.dX = dX;
}
public void setdY(float dY) {
this.dY = dY;
}
public void setdZ(float dZ) {
this.dZ = dZ;
}
}
Calibrating accelerometer must be called before each experiment. Phone orientation must not be changed while measuring.
To calibrate accelerometer, i use this class:
public class Calibrator {
final static int UPDATE_INTERVAL = 400;
final static int ITERATIONS = 5;
Handler hRefresh;
XYZAccelerometer acc;
int eventNumber;
private LinkedList calData;
public Calibrator(Handler hRefresh, XYZAccelerometer acc, int eventNumber) {
this.hRefresh = hRefresh;
this.acc = acc;
this.eventNumber = eventNumber;
}
public void calibrate() {
final Timer calTimer = new Timer();
calData = new LinkedList();
acc.setdX(0);
acc.setdY(0);
acc.setdZ(0);
calTimer.scheduleAtFixedRate(
new TimerTask() {
public void run() {
addCalData(calData);
if (calData.size() > ITERATIONS) {
calTimer.cancel();
try {
calSensor(calData);
} catch (Exception ex) {
try {
throw ex;
} catch (Exception ex1) {
hRefresh.sendEmptyMessage(5);
}
}
hRefresh.sendEmptyMessage(eventNumber);
}
}
},
0,
UPDATE_INTERVAL);
}
private void addCalData(LinkedList cD) {
Point p = acc.getPoint();
cD.add(p);
acc.reset();
}
private void calSensor(LinkedList cD) throws Exception {
if (cD.size() < ITERATIONS-1) {
throw new Exception("not enough data to calibrate");
}
float x = 0;
float y = 0;
float z = 0;
// Don't use first measure
for (int i = 1; i < cD.size(); ++i) {
x += cD.get(i).getX();
y += cD.get(i).getY();
z += cD.get(i).getZ();
}
x = x / (cD.size() - 1);
y = y / (cD.size() - 1);
z = z / (cD.size() - 1);
acc.setdX(-x);
acc.setdY(-y);
acc.setdZ(-z);
}
}
maintenance class to keep data of one measure
public class Point {
private float x = 0;
private float y = 0;
private float z = 0;
private int cnt = 1;
public float getX() {
return x/(float)cnt;
}
public float getY() {
return y/(float)cnt;
}
public float getZ() {
return z/(float)cnt;
}
public Point(float x, float y, float z, int cnt) {
this.x = x;
this.y = y;
this.z = z;
this.cnt = cnt;
}
public float getForce(){
return getX()*getX()+getY()*getY()+getZ()*getZ();
}
}
And class to process data of measure
public class MeasurePoint {
private float x;
private float y;
private float z;
private float speedBefore;
private float speedAfter;
private float distance;
private float acceleration;
private long interval;
private Point averagePoint;
public MeasurePoint(float x, float y, float z, float speedBefore, long interval, Point averagePoint) {
this.x = x;
this.y = y;
this.z = z;
this.speedBefore = speedBefore;
this.interval = interval;
this.averagePoint = averagePoint;
speedAfter = 0;
calc();
}
private void calc(){
//Acceleration as projection of current vector on average
acceleration = this.x*averagePoint.getX() +
this.y*averagePoint.getY() +
this.z*averagePoint.getZ();
acceleration = acceleration / ((float)Math.sqrt(averagePoint.getForce()));
float t = ((float)interval / 1000f);
speedAfter = speedBefore + acceleration * t;
distance = speedBefore*t + acceleration*t*t/2;
}
public String getStoreString(){
String s = "write here whatever you want";
return s;
}
// add getters
}
This one - to store and save data array
public class MeasureData {
// points from accelerometr
private LinkedList accData;
private LinkedList data;
// timer interval of generating points
private long interval;
public MeasureData(long interval) {
this.interval = interval;
accData = new LinkedList ();
data = new LinkedList ();
}
public void addPoint(Point p){
accData.add(p);
}
public void process(){
for(int i = 0; i < accData.size(); ++i){
Point p = accData.get(i);
float speed = 0;
if(i > 0){
speed = data.get(i-1).getSpeedAfter();
}
data.add(new MeasurePoint(p.getX(), p.getY(), p.getZ(), speed, interval, getAveragePoint()));
}
}
public boolean saveExt(Context con, String fname) throws Throwable {
try {
File file = new File(con.getExternalFilesDir(null), fname);
FileOutputStream os = new FileOutputStream(file);
OutputStreamWriter out = new OutputStreamWriter(os);
for (int i = 0; i < data.size(); ++i) {
MeasurePoint m = data.get(i);
out.write(m.getStoreString());
}
out.close();
} catch (Throwable t) {
throw (t);
}
return true;
}
private Point getAveragePoint() {
float x = 0;
float y = 0;
float z = 0;
for(int i = 0; i < accData.size(); ++i){
Point p = accData.get(i);
x += p.getX();
y += p.getY();
z += p.getZ();
}
return new Point(x, y, z, 1);
}
public float getLastSpeed(){
return data.getLast().getSpeedAfter();
}
public float getLastSpeedKm(){
float ms = getLastSpeed();
return ms*3.6f;
}
}
And, finally, how to use all this in your activity(I cleaned it up a lot, sorry if it will not complie - fill free to write it in comments:
public class TestActivity extends Activity {
static final int TIMER_DONE = 2;
static final int START = 3;
static final int CAL_TIMER_DONE = 4;
static final int ERROR = 5;
private StartCatcher mStartListener;
private XYZAccelerometer xyzAcc;
private SensorManager mSensorManager;
private static final long UPDATE_INTERVAL = 500;
private static final long MEASURE_TIMES = 20;
private Timer timer;
private TextView tv;
private Button testBtn;
int counter;
private MeasureData mdXYZ;
/** handler for async events*/
Handler hRefresh = new Handler() {
#Override
public void handleMessage(Message msg) {
switch (msg.what) {
case TIMER_DONE:
onMeasureDone();
String es1 = Float.toString(Math.round(mdXYZ.getLastSpeedKm()*100)/100f);
tv.append(" END SPEED " + es1 + " " + es2 + " \n");
enableButtons();
break;
case START:
tv.append(" START");
timer = new Timer();
timer.scheduleAtFixedRate(
new TimerTask() {
public void run() {
dumpSensor();
}
},
0,
UPDATE_INTERVAL);
break;
case ERROR:
Toast.makeText(getApplicationContext(), "ERROR", Toast.LENGTH_SHORT).show();
break;
}
}
};
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
tv = (TextView) findViewById(R.id.txt);
testBtn = (Button) findViewById(R.id.btn);
}
#Override
protected void onResume() {
super.onResume();
tv.append("\n ..");
mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
setAccelerometer();
setStartCatcher();
mSensorManager.registerListener(xyzAcc,
mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),
SensorManager.SENSOR_DELAY_GAME);
}
#Override
protected void onPause() {
mSensorManager.unregisterListener(xyzAcc);
super.onPause();
}
public void onButtonTest(View v) {
disableButtons();
mdXYZ = new MeasureData(UPDATE_INTERVAL);
counter = 0;
tv.setText("");
tv.append("Calibrating");
Calibrator cal = new Calibrator(hRefresh, xyzAcc, START);
cal.calibrate();
}
void dumpSensor() {
++counter;
mdXYZ.addPoint(xyzAcc.getPoint());
hRefresh.sendEmptyMessage(TICK);
if (counter > MEASURE_TIMES) {
timer.cancel();
hRefresh.sendEmptyMessage(TIMER_DONE);
}
}
private void enableButtons() {
testBtn.setEnabled(true);
}
private void setAccelerometer() {
xyzAcc = new XYZAccelerometer();
mSensorManager.registerListener(xyzAcc,
mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),
SensorManager.SENSOR_DELAY_UI);
}
private void disableButtons() {
testBtn.setEnabled(false);
}
private void onMeasureDone() {
try {
mdXYZ.process();
long now = System.currentTimeMillis();
mdXYZ.saveExt(this, Long.toString(now) + ".csv");
} catch (Throwable ex) {
Toast.makeText(this, ex.getMessage().toString(), Toast.LENGTH_SHORT);
}
}
}
<serviceLinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<serviceButton
android:id="#+id/btn"
android:text="TEST"
android:layout_width="300px"
android:layout_height="200px"
android:onClick="onButtonTest" />
<serviceTextView
android:id = "#+id/txt"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text=":"
/>
<service/LinearLayout>

Although at the developer.android.com site it is stated clearly that
you could use the linear accelerometer to see how fast your car is going"
But I did not find anything (in testing or in examples or code) that showed this is really true.
Now, unfortunately, I am convinced that it is not possible to calculate the speed of a car with the linear accelerometer.

Please see the below code to get the velocity using accelerometer
public class SensorTestActivity extends Activity implements SensorEventListener {
double calibration = Double.NaN;
private SensorManager sensorManager;
private boolean color = false;
private TextView view;
private long lastUpdate;
float appliedAcceleration = 0;
float currentAcceleration = 0;
float velocity = 0;
Date lastUpdatedate;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
view = findViewById(R.id.textView);
// view.setBackgroundColor(Color.GREEN);
lastUpdatedate = new Date(System.currentTimeMillis());
sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
lastUpdate = System.currentTimeMillis();
}
#Override
public void onSensorChanged(SensorEvent event) {
// if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
// getAccelerometer(event);
// }
double x = event.values[0];
double y = event.values[1];
double z = event.values[2];
double a = Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2) + Math.pow(z, 2));
if (calibration == Double.NaN)
calibration = a;
else {
updateVelocity();
currentAcceleration = (float)a;
}
}
private void getAccelerometer(SensorEvent event) {
float[] values = event.values;
// Movement
float x = values[0];
float y = values[1];
float z = values[2];
float accelationSquareRoot = (x * x + y * y + z * z)
/ (SensorManager.GRAVITY_EARTH * SensorManager.GRAVITY_EARTH);
long actualTime = event.timestamp;
if (accelationSquareRoot >= 2) //
{
if (actualTime - lastUpdate < 200) {
return;
}
lastUpdate = actualTime;
// Toast.makeText(this, "Device was shuffed", Toast.LENGTH_SHORT)
// .show();
if (color) {
view.setBackgroundColor(Color.GREEN);
} else {
view.setBackgroundColor(Color.RED);
}
color = !color;
view.setText("SPEEDDDDD=== "+accelationSquareRoot);
// Log.i("SensorTestActivity","SPEEDDDDD=== "+accelationSquareRoot+" ");
}
}
private void updateVelocity() {
// Calculate how long this acceleration has been applied.
Date timeNow = new Date(System.currentTimeMillis());
long timeDelta = timeNow.getTime()-lastUpdatedate.getTime();
lastUpdatedate.setTime(timeNow.getTime());
// Calculate the change in velocity at the
// current acceleration since the last update.
float deltaVelocity = appliedAcceleration * (timeDelta/1000);
appliedAcceleration = currentAcceleration;
// Add the velocity change to the current velocity.
velocity += deltaVelocity;
final double mph = (Math.round(100*velocity / 1.6 * 3.6))/100;
Log.i("SensorTestActivity","SPEEDDDDD=== "+mph+" "+velocity);
}
#Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
}
#Override
protected void onResume() {
super.onResume();
// register this class as a listener for the orientation and
// accelerometer sensors
sensorManager.registerListener(this,
sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),
SensorManager.SENSOR_DELAY_NORMAL);
}
#Override
protected void onPause() {
// unregister listener
super.onPause();
sensorManager.unregisterListener(this);
}
}

Android RotationSensor returns positive values but no negative values ? on y axis

I need help with onSensorChanged(SensorEvent event). I can get a toast message when device is facedown (y axis) 0 to 180.but can not get it to work going the other way on the (y axis) -0 to -180 faceup. Any help is greatly appreciated.
Thanks for your interest,
Mike
Relevant code follows:
public class MainActivity extends Activity implements SensorEventListener {
private SensorManager mSensorManager;
private Sensor mRotationSensor;
private double[] values;
private String TAG;
private static final int SENSOR_DELAY = 500 * 1000; // 500ms
private static final int FROM_RADS_TO_DEGS = -57;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
try {
mSensorManager = (SensorManager) getSystemService(Activity.SENSOR_SERVICE);
mRotationSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ROTATION_VECTOR);
mSensorManager.registerListener(this, mRotationSensor, SENSOR_DELAY);
} catch (Exception e) {
Toast.makeText(this, "Hardware compatibility issue", Toast.LENGTH_LONG).show();
}
}
#Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
// TODO Auto-generated method stub
}
#Override
public void onSensorChanged(SensorEvent event) {
if (event.sensor == mRotationSensor) {
if (event.values.length > 4) {
float[] truncatedRotationVector = new float[4];
System.arraycopy(event.values, 0, truncatedRotationVector, 0, 4);
update(truncatedRotationVector);
} else {
update(event.values);
}
}
}
private void update(float[] vectors) {
float[] rotationMatrix = new float[9];
SensorManager.getRotationMatrixFromVector(rotationMatrix, vectors);
int worldAxisX = SensorManager.AXIS_X;
int worldAxisZ = SensorManager.AXIS_Z;
float[] adjustedRotationMatrix = new float[9];
SensorManager.remapCoordinateSystem(rotationMatrix, worldAxisX, worldAxisZ, adjustedRotationMatrix);
float[] orientation = new float[3];
SensorManager.getOrientation(adjustedRotationMatrix, orientation);
float pitch = orientation[1] * FROM_RADS_TO_DEGS;
float roll = orientation[2] * FROM_RADS_TO_DEGS;
((TextView)findViewById(R.id.pitch)).setText("Pitch: "+pitch);
((TextView)findViewById(R.id.roll)).setText("Roll: "+roll);
if (pitch <= 81 && pitch >= 50) {
// mostly vertical
Toast.makeText(this, "Device Face Down ", Toast.LENGTH_SHORT).show();
}
{
if (pitch < -81&& pitch >= -50) {
Toast.makeText(this, "Device Face Up", Toast.LENGTH_SHORT).show();
}} }

unable to make 2nd circle follow its own path

I am unable to create more circles which follows its own path with drawCircle .
I have used the code below which creates another circle but follows the path along the lines of 1st circle but not independent .How do I move both circles independent of each other?
I have added
c.drawCircle(ballX-100, ballY-100, 50, ballPaintyellow);
How do I make the above circle independent from the 1st circle?. I really appreciate any help.Thanks in Advance.
BouncingBallActivity.java
package com.stuffthathappens.games;
import static android.hardware.SensorManager.DATA_X;
import static android.hardware.SensorManager.DATA_Y;
import static android.hardware.SensorManager.SENSOR_ACCELEROMETER;
import static android.hardware.SensorManager.SENSOR_DELAY_GAME;
import java.util.concurrent.TimeUnit;
import android.app.Activity;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.hardware.SensorListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.os.Vibrator;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.SurfaceHolder.Callback;
/**
* This activity shows a ball that bounces around. The phone's
* accelerometer acts as gravity on the ball. When the ball hits
* the edge, it bounces back and triggers the phone vibrator.
*/
#SuppressWarnings("deprecation")
public class BouncingBallActivity extends Activity implements Callback, SensorListener {
private static final int BALL_RADIUS =20;
private SurfaceView surface;
private SurfaceHolder holder;
private final BouncingBallModel model = new BouncingBallModel(BALL_RADIUS);
private GameLoop gameLoop;
private Paint backgroundPaint;
private Paint ballPaint;
private SensorManager sensorMgr;
private long lastSensorUpdate = -1;
private Paint ballPaintyellow;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.bouncing_ball);
surface = (SurfaceView) findViewById(R.id.bouncing_ball_surface);
holder = surface.getHolder();
surface.getHolder().addCallback(this);
backgroundPaint = new Paint();
backgroundPaint.setColor(Color.WHITE);
ballPaint = new Paint();
ballPaint.setColor(Color.BLUE);
ballPaint.setAntiAlias(true);
ballPaintyellow = new Paint();
ballPaintyellow.setColor(Color.YELLOW);
ballPaintyellow.setAntiAlias(true);
}
#Override
protected void onPause() {
super.onPause();
model.setVibrator(null);
sensorMgr.unregisterListener(this, SENSOR_ACCELEROMETER);
sensorMgr = null;
model.setAccel(0, 0);
}
#Override
protected void onResume() {
super.onResume();
sensorMgr = (SensorManager) getSystemService(SENSOR_SERVICE);
boolean accelSupported = sensorMgr.registerListener(this,
SENSOR_ACCELEROMETER,
SENSOR_DELAY_GAME);
if (!accelSupported) {
// on accelerometer on this device
sensorMgr.unregisterListener(this, SENSOR_ACCELEROMETER);
// TODO show an error
}
// NOTE 1: you cannot get system services before onCreate()
// NOTE 2: AndroidManifest.xml must contain this line:
// <uses-permission android:name="android.permission.VIBRATE"/>
Vibrator vibrator = (Vibrator) getSystemService(Activity.VIBRATOR_SERVICE);
model.setVibrator(vibrator);
}
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
model.setSize(width, height);
}
public void surfaceCreated(SurfaceHolder holder) {
gameLoop = new GameLoop();
gameLoop.start();
}
private void draw() {
// thread safety - the SurfaceView could go away while we are drawing
Canvas c = null;
try {
// NOTE: in the LunarLander they don't have any synchronization here,
// so I guess this is OK. It will return null if the holder is not ready
c = holder.lockCanvas();
// this needs to synchronize on something
if (c != null) {
doDraw(c);
}
} finally {
if (c != null) {
holder.unlockCanvasAndPost(c);
}
}
}
private void doDraw(Canvas c) {
int width = c.getWidth();
int height = c.getHeight();
c.drawRect(0, 0, width, height, backgroundPaint);
float ballX, ballY;
synchronized (model.LOCK) {
ballX = model.ballPixelX;
ballY = model.ballPixelY;
}
c.drawCircle(ballX, ballY, BALL_RADIUS, ballPaint);
c.drawCircle(ballX-100, ballY-100, 50, ballPaintyellow);
}
public void surfaceDestroyed(SurfaceHolder holder) {
try {
model.setSize(0,0);
gameLoop.safeStop();
} finally {
gameLoop = null;
}
}
private class GameLoop extends Thread {
private volatile boolean running = true;
public void run() {
while (running) {
try {
// don't like this hardcoding
TimeUnit.MILLISECONDS.sleep(5);
draw();
model.updatePhysics();
} catch (InterruptedException ie) {
running = false;
}
}
}
public void safeStop() {
running = false;
interrupt();
}
}
public void onAccuracyChanged(int sensor, int accuracy) {
}
public void onSensorChanged(int sensor, float[] values) {
if (sensor == SENSOR_ACCELEROMETER) {
long curTime = System.currentTimeMillis();
// only allow one update every 50ms, otherwise updates
// come way too fast
if (lastSensorUpdate == -1 || (curTime - lastSensorUpdate) > 50) {
lastSensorUpdate = curTime;
model.setAccel(values[DATA_X], values[DATA_Y]);
}
}
}
}
Bouncingballmodel.java
package com.stuffthathappens.games;
import java.util.concurrent.atomic.AtomicReference;
import android.os.Vibrator;
/**
* This data model tracks the width and height of the playing field along
* with the current position of a ball.
*/
public class BouncingBallModel {
// the ball speed is meters / second. When we draw to the screen,
// 1 pixel represents 1 meter. That ends up too slow, so multiply
// by this number. Bigger numbers speeds things up.
private final float pixelsPerMeter = 10;
private final int ballRadius;
// these are public, so make sure you synchronize on LOCK
// when reading these. I made them public since you need to
// get both X and Y in pairs, and this is more efficient than
// getter methods. With two getters, you'd still need to
// synchronize.
public float ballPixelX, ballPixelY;
private int pixelWidth, pixelHeight;
// values are in meters/second
private float velocityX, velocityY;
// typical values range from -10...10, but could be higher or lower if
// the user moves the phone rapidly
private float accelX, accelY;
/**
* When the ball hits an edge, multiply the velocity by the rebound.
* A value of 1.0 means the ball bounces with 100% efficiency. Lower
* numbers simulate balls that don't bounce very much.
*/
private static final float rebound = 0.8f;
// if the ball bounces and the velocity is less than this constant,
// stop bouncing.
private static final float STOP_BOUNCING_VELOCITY = 2f;
private volatile long lastTimeMs = -1;
public final Object LOCK = new Object();
private AtomicReference<Vibrator> vibratorRef =
new AtomicReference<Vibrator>();
public BouncingBallModel(int ballRadius) {
this.ballRadius = ballRadius;
}
public void setAccel(float ax, float ay) {
synchronized (LOCK) {
this.accelX = ax;
this.accelY = ay;
}
}
public void setSize(int width, int height) {
synchronized (LOCK) {
this.pixelWidth = width;
this.pixelHeight = height;
}
}
public int getBallRadius() {
return ballRadius;
}
/**
* Call this to move the ball to a particular location on the screen. This
* resets the velocity to zero, but the acceleration doesn't change so
* the ball should start falling shortly.
*/
public void moveBall(int ballX, int ballY) {
synchronized (LOCK) {
this.ballPixelX = ballX;
this.ballPixelY = ballY;
velocityX = 0;
velocityY = 0;
}
}
public void updatePhysics() {
// copy everything to local vars (hence the 'l' prefix)
float lWidth, lHeight, lBallX, lBallY, lAx, lAy, lVx, lVy;
synchronized (LOCK) {
lWidth = pixelWidth;
lHeight = pixelHeight;
lBallX = ballPixelX;
lBallY = ballPixelY;
lVx = velocityX;
lVy = velocityY;
lAx = accelX;
lAy = -accelY;
}
if (lWidth <= 0 || lHeight <= 0) {
// invalid width and height, nothing to do until the GUI comes up
return;
}
long curTime = System.currentTimeMillis();
if (lastTimeMs < 0) {
lastTimeMs = curTime;
return;
}
long elapsedMs = curTime - lastTimeMs;
lastTimeMs = curTime;
// update the velocity
// (divide by 1000 to convert ms to seconds)
// end result is meters / second
lVx += ((elapsedMs * lAx) / 1000) * pixelsPerMeter;
lVy += ((elapsedMs * lAy) / 1000) * pixelsPerMeter;
// update the position
// (velocity is meters/sec, so divide by 1000 again)
lBallX += ((lVx * elapsedMs) / 1000) * pixelsPerMeter;
lBallY += ((lVy * elapsedMs) / 1000) * pixelsPerMeter;
boolean bouncedX = false;
boolean bouncedY = false;
if (lBallY - ballRadius < 0) {
lBallY = ballRadius;
lVy = -lVy * rebound;
bouncedY = true;
} else if (lBallY + ballRadius > lHeight) {
lBallY = lHeight - ballRadius;
lVy = -lVy * rebound;
bouncedY = true;
}
if (bouncedY && Math.abs(lVy) < STOP_BOUNCING_VELOCITY) {
lVy = 0;
bouncedY = false;
}
if (lBallX - ballRadius < 0) {
lBallX = ballRadius;
lVx = -lVx * rebound;
bouncedX = true;
} else if (lBallX + ballRadius > lWidth) {
lBallX = lWidth - ballRadius;
lVx = -lVx * rebound;
bouncedX = true;
}
if (bouncedX && Math.abs(lVx) < STOP_BOUNCING_VELOCITY) {
lVx = 0;
bouncedX = false;
}
// safely copy local vars back to object fields
synchronized (LOCK) {
ballPixelX = lBallX;
ballPixelY = lBallY;
velocityX = lVx;
velocityY = lVy;
}
if (bouncedX || bouncedY) {
Vibrator v = vibratorRef.get();
if (v != null) {
v.vibrate(20L);
}
}
}
public void setVibrator(Vibrator v) {
vibratorRef.set(v);
}
}

Which view you are using has nothing to do with it ....
At the moment you have only one BouncingBallModel
private final BouncingBallModel model = new BouncingBallModel(BALL_RADIUS);
This is the one you see when you draw something. Now if you want to draw multiple balls, you will need many BouncingBallModel. So either create a BouncingBallModel model2 or make it dynamic using an array.
Then iterate over the array and draw each ball.

unable to add circles to canvas dynamically

I tried to make a single ball bouncing to dynamic ball bouncing . Eg: here the number of circles is 50.
But I am getting error while trying to make the circles dynamic (Model) .How do I make it work and make the model/circle dynamic.In this case 50 circles ? I really appreciate any help. Thanks in Advance.
package com.stuffthathappens.games;
import static android.hardware.SensorManager.DATA_X;
import static android.hardware.SensorManager.DATA_Y;
import static android.hardware.SensorManager.SENSOR_ACCELEROMETER;
import static android.hardware.SensorManager.SENSOR_DELAY_GAME;
import java.util.concurrent.TimeUnit;
import android.app.Activity;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.hardware.SensorListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.os.Vibrator;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.SurfaceHolder.Callback;
/**
* This activity shows a ball that bounces around. The phone's
* accelerometer acts as gravity on the ball. When the ball hits
* the edge, it bounces back and triggers the phone vibrator.
*/
#SuppressWarnings("deprecation")
public class BouncingBallActivity extends Activity implements Callback, SensorListener {
private static final int BALL_RADIUS =20;
private SurfaceView surface;
private SurfaceHolder holder;
private GameLoop gameLoop;
private Paint backgroundPaint;
private Paint ballPaint;
private SensorManager sensorMgr;
private long lastSensorUpdate = -1;
private Paint ballPaintyellow;
private BouncingBallModel[] model;
int Totalcircles=50;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.bouncing_ball);
for (int i = 0; i < Totalcircles; i++) {
model[i] = new BouncingBallModel(BALL_RADIUS);
}
surface = (SurfaceView) findViewById(R.id.bouncing_ball_surface);
holder = surface.getHolder();
surface.getHolder().addCallback(this);
backgroundPaint = new Paint();
backgroundPaint.setColor(Color.WHITE);
ballPaint = new Paint();
ballPaint.setColor(Color.BLUE);
ballPaint.setAntiAlias(true);
ballPaintyellow = new Paint();
ballPaintyellow.setColor(Color.YELLOW);
ballPaintyellow.setAntiAlias(true);
}
#Override
protected void onPause() {
super.onPause();
for (int i = 0; i < Totalcircles; i++) {
model[i].setVibrator(null);
}
sensorMgr.unregisterListener(this, SENSOR_ACCELEROMETER);
sensorMgr = null;
for (int i = 0; i < Totalcircles; i++) {
model[i].setAccel(0, 0);
}
}
#Override
protected void onResume() {
super.onResume();
sensorMgr = (SensorManager) getSystemService(SENSOR_SERVICE);
boolean accelSupported = sensorMgr.registerListener(this,
SENSOR_ACCELEROMETER,
SENSOR_DELAY_GAME);
if (!accelSupported) {
// on accelerometer on this device
sensorMgr.unregisterListener(this, SENSOR_ACCELEROMETER);
// TODO show an error
}
// NOTE 1: you cannot get system services before onCreate()
// NOTE 2: AndroidManifest.xml must contain this line:
// <uses-permission android:name="android.permission.VIBRATE"/>
Vibrator vibrator = (Vibrator) getSystemService(Activity.VIBRATOR_SERVICE);
for (int i = 0; i < Totalcircles; i++) {
model[i].setVibrator(vibrator);
}
}
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
for (int i = 0; i < Totalcircles; i++) {
model[i].setSize(width, height);
}
}
public void surfaceCreated(SurfaceHolder holder) {
gameLoop = new GameLoop();
gameLoop.start();
}
private void draw() {
// thread safety - the SurfaceView could go away while we are drawing
Canvas c = null;
try {
// NOTE: in the LunarLander they don't have any synchronization here,
// so I guess this is OK. It will return null if the holder is not ready
c = holder.lockCanvas();
// this needs to synchronize on something
if (c != null) {
doDraw(c);
}
} finally {
if (c != null) {
holder.unlockCanvasAndPost(c);
}
}
}
private void doDraw(Canvas c) {
int width = c.getWidth();
int height = c.getHeight();
c.drawRect(0, 0, width, height, backgroundPaint);
///
float ballX[]=new float[50], ballY[]=new float[50];
for (int i = 0; i < Totalcircles; i++) {
synchronized (model[i].LOCK) {
ballX[i] = model[i].ballPixelX;
ballY[i] = model[i].ballPixelY;
}
}
//
for (int i = 0; i < Totalcircles; i++) {
c.drawCircle(ballX[i], ballY[i], BALL_RADIUS, ballPaint);
}
}
public void surfaceDestroyed(SurfaceHolder holder) {
try {
for (int i = 0; i < Totalcircles; i++) {
model[i].setSize(0,0);
}
gameLoop.safeStop();
} finally {
gameLoop = null;
}
}
private class GameLoop extends Thread {
private volatile boolean running = true;
public void run() {
while (running) {
try {
// don't like this hardcoding
TimeUnit.MILLISECONDS.sleep(5);
draw();
for (int i = 0; i < Totalcircles; i++) {
model[i].updatePhysics();
}
} catch (InterruptedException ie) {
running = false;
}
}
}
public void safeStop() {
running = false;
interrupt();
}
}
public void onAccuracyChanged(int sensor, int accuracy) {
}
public void onSensorChanged(int sensor, float[] values) {
if (sensor == SENSOR_ACCELEROMETER) {
long curTime = System.currentTimeMillis();
// only allow one update every 50ms, otherwise updates
// come way too fast
if (lastSensorUpdate == -1 || (curTime - lastSensorUpdate) > 50) {
lastSensorUpdate = curTime;
for (int i = 0; i < Totalcircles; i++) {
model[i].setAccel(values[DATA_X], values[DATA_Y]);
}
}
}
}
}
model.java
package com.stuffthathappens.games;
import java.util.concurrent.atomic.AtomicReference;
import android.os.Vibrator;
/**
* This data model tracks the width and height of the playing field along
* with the current position of a ball.
*/
public class BouncingBallModel {
// the ball speed is meters / second. When we draw to the screen,
// 1 pixel represents 1 meter. That ends up too slow, so multiply
// by this number. Bigger numbers speeds things up.
private final float pixelsPerMeter = 10;
private final int ballRadius;
// these are public, so make sure you synchronize on LOCK
// when reading these. I made them public since you need to
// get both X and Y in pairs, and this is more efficient than
// getter methods. With two getters, you'd still need to
// synchronize.
public float ballPixelX, ballPixelY;
private int pixelWidth, pixelHeight;
// values are in meters/second
private float velocityX, velocityY;
// typical values range from -10...10, but could be higher or lower if
// the user moves the phone rapidly
private float accelX, accelY;
/**
* When the ball hits an edge, multiply the velocity by the rebound.
* A value of 1.0 means the ball bounces with 100% efficiency. Lower
* numbers simulate balls that don't bounce very much.
*/
private static final float rebound = 0.8f;
// if the ball bounces and the velocity is less than this constant,
// stop bouncing.
private static final float STOP_BOUNCING_VELOCITY = 2f;
private volatile long lastTimeMs = -1;
public final Object LOCK = new Object();
private AtomicReference<Vibrator> vibratorRef =
new AtomicReference<Vibrator>();
public BouncingBallModel(int ballRadius) {
this.ballRadius = ballRadius;
}
public void setAccel(float ax, float ay) {
synchronized (LOCK) {
this.accelX = ax;
this.accelY = ay;
}
}
public void setSize(int width, int height) {
synchronized (LOCK) {
this.pixelWidth = width;
this.pixelHeight = height;
}
}
public int getBallRadius() {
return ballRadius;
}
/**
* Call this to move the ball to a particular location on the screen. This
* resets the velocity to zero, but the acceleration doesn't change so
* the ball should start falling shortly.
*/
public void moveBall(int ballX, int ballY) {
synchronized (LOCK) {
this.ballPixelX = ballX;
this.ballPixelY = ballY;
velocityX = 0;
velocityY = 0;
}
}
public void updatePhysics() {
// copy everything to local vars (hence the 'l' prefix)
float lWidth, lHeight, lBallX, lBallY, lAx, lAy, lVx, lVy;
synchronized (LOCK) {
lWidth = pixelWidth;
lHeight = pixelHeight;
lBallX = ballPixelX;
lBallY = ballPixelY;
lVx = velocityX;
lVy = velocityY;
lAx = accelX;
lAy = -accelY;
}
if (lWidth <= 0 || lHeight <= 0) {
// invalid width and height, nothing to do until the GUI comes up
return;
}
long curTime = System.currentTimeMillis();
if (lastTimeMs < 0) {
lastTimeMs = curTime;
return;
}
long elapsedMs = curTime - lastTimeMs;
lastTimeMs = curTime;
// update the velocity
// (divide by 1000 to convert ms to seconds)
// end result is meters / second
lVx += ((elapsedMs * lAx) / 1000) * pixelsPerMeter;
lVy += ((elapsedMs * lAy) / 1000) * pixelsPerMeter;
// update the position
// (velocity is meters/sec, so divide by 1000 again)
lBallX += ((lVx * elapsedMs) / 1000) * pixelsPerMeter;
lBallY += ((lVy * elapsedMs) / 1000) * pixelsPerMeter;
boolean bouncedX = false;
boolean bouncedY = false;
if (lBallY - ballRadius < 0) {
lBallY = ballRadius;
lVy = -lVy * rebound;
bouncedY = true;
} else if (lBallY + ballRadius > lHeight) {
lBallY = lHeight - ballRadius;
lVy = -lVy * rebound;
bouncedY = true;
}
if (bouncedY && Math.abs(lVy) < STOP_BOUNCING_VELOCITY) {
lVy = 0;
bouncedY = false;
}
if (lBallX - ballRadius < 0) {
lBallX = ballRadius;
lVx = -lVx * rebound;
bouncedX = true;
} else if (lBallX + ballRadius > lWidth) {
lBallX = lWidth - ballRadius;
lVx = -lVx * rebound;
bouncedX = true;
}
if (bouncedX && Math.abs(lVx) < STOP_BOUNCING_VELOCITY) {
lVx = 0;
bouncedX = false;
}
// safely copy local vars back to object fields
synchronized (LOCK) {
ballPixelX = lBallX;
ballPixelY = lBallY;
velocityX = lVx;
velocityY = lVy;
}
if (bouncedX || bouncedY) {
Vibrator v = vibratorRef.get();
if (v != null) {
v.vibrate(20L);
}
}
}
public void setVibrator(Vibrator v) {
vibratorRef.set(v);
}
}
Logcat error:
FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.stuffthathappens.games/com.stuffthathappens.games.BouncingBallActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2194)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2229)
at android.app.ActivityThread.access$600(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1261)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:4945)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.stuffthathappens.games.BouncingBallActivity.onCreate(BouncingBallActivity.java:52)
at android.app.Activity.performCreate(Activity.java:4531)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1071)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2150)

You can declare you array like this:
private BouncingBallModel[] model = new BouncingBallModel[50];
like the following
How do I declare and initialize an array in Java?

Moving image when wave hand in front of camera using opencv for android

i'm trying to implement like this in my application
http://www.youtube.com/watch?v=QrXwJIco4w8
but it seems i don't really get the idea how to do it..
seems i must use motion tracking and hand recognition, also communicate with front-end camera, but mostly link that i found only show detect OUTSIDE object not INSIDE object(means inside device).
so what i want is if there is object(like image or anything) in application, then when i move my hand in front of camera like go to left, then the image position also go to left.
Make the image move without interact with touch but using camera instead(touchless)
Can you help me show way to do it?
thanks

I dont know about camera but I do have an alternative idea for using wave gestures to change image etc.
You can use the proximity sensor on the phone. But it cannot understand that you moved your hand from left to right or right to left. So, you can have something like this:
Moving once over sensor - left to right
Moving twice over sensor - right to left
You can define proximity sensor something like this:
public class ProximityNotifier implements SensorEventListener{
private final SensorManager mSensorManager;
private final Sensor mProximitySensor;
private final Sensor mAccelSensor;
private float mProximityMax = 0.0f;
private boolean mStartProxComparison;
public float mProximityValue = 0.0f;
private long lastBlockedTimestamp = 0;
private long gapPlayPause = 0;
private long gapNext = 0;
private static float mValue0 = 0.0f;
private static float mValue1 = 0.0f;
private ProximityNotifier.Callback cb = null;
private static final String TAG = "ProximityNotifier";
public ProximityNotifier(Context ctxt, ProximityNotifier.Callback cb, long gap1, long gap2) {
this.cb = cb;
this.gapPlayPause = gap1;
this.gapNext = gap2;
mSensorManager = (SensorManager)ctxt.getSystemService(Context.SENSOR_SERVICE);
mProximitySensor = mSensorManager.getDefaultSensor(Sensor.TYPE_PROXIMITY);
mAccelSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
if (null != mProximitySensor)
mProximityMax = mProximitySensor.getMaximumRange();
mProximityValue = mProximityMax;
startProximityNotifier();
}
public interface Callback {
void pageChange();
}
public void startProximityNotifier() {
if(null != mSensorManager) {
if ((null != mProximitySensor) && (null != mAccelSensor)) {
mSensorManager.registerListener(this, mProximitySensor, SensorManager.SENSOR_DELAY_UI);
mSensorManager.registerListener(this, mAccelSensor, SensorManager.SENSOR_DELAY_UI);
mStartProxComparison = true;
}
else
mStartProxComparison = false;
}
}
public void stopProximityNotifier() {
if(null != mSensorManager) {
if ((null != mProximitySensor) && (null != mAccelSensor)) {
mSensorManager.unregisterListener(this, mProximitySensor);
mSensorManager.unregisterListener(this, mAccelSensor);
}
}
}
public void onAccuracyChanged(Sensor sensor, int accuracy) {
}
public void onSensorChanged(SensorEvent sensorEvent) {
if (sensorEvent.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
mValue0 = sensorEvent.values[0];
mValue1 = sensorEvent.values[1];
}
if ((sensorEvent.sensor.getType() == Sensor.TYPE_PROXIMITY) &&
((mValue0 < 2) && (mValue0 > -2)) &&
((mValue1 < 2) && (mValue1 > -2))) {
// check for a max -> 0 transition
if((mStartProxComparison == true) && ((mProximityValue == mProximityMax) && (sensorEvent.values[0] == 0))) {
lastBlockedTimestamp = SystemClock.uptimeMillis();
}
else {
long now = SystemClock.uptimeMillis();
if (lastBlockedTimestamp != 0) {
/*if ((now - lastBlockedTimestamp) > gapPlayPause) {
if (cb != null) {
//cb.gesturePlayPause();
}
}else*/ if ((now - lastBlockedTimestamp) > gapNext){
if (cb != null)
cb.pageChange();
}
}
lastBlockedTimestamp = 0;
}
mProximityValue = sensorEvent.values[0];
}
}
}
and in your activity you can declare and use like this:
mProximityNotifier = new ProximityNotifier(this, this, 400, 200);
//Callback method for Proximity Sensor
public void pageChange() {
//call for image change
}
Hope it helps you