iOS Accelerometer-Based Gesture Recognition - iphone

Question

I want to create a project that reads the user's gesture (accelerometer-based) and recognise it, I searched a lot but all I found was too old, I neither have problems in classifying nor in recognition, I will use 1 dollar recogniser or HMM, I just want to know how to read the user's gesture using the accelerometer.
Is the accelerometer data (x,y,z values) enough or should i use other data with it like Attitude data (roll, pitch, yaw), Gyro data or magnitude data, I don't even understand anyone of them so explaining what does these sensors do will be useful.
Thanks in advance !

Answer 1

Finally i did it, i used userAcceleration data which is device acceleration due to device excluding gravity, i found a lot of people use the normal acceleration data and do a lot of math to remove gravity from it, now it's already done by iOS 6 in userAcceleration.
And i used 1$ recognizer which is a 2D recongnizer (i.e. point(5, 10), no Z).Here's a link for 1$ recognizer, there's a c++ version of it in the downloads section.
Here are the steps of my code...
Read userAcceleration data with frequancy 50 HZ.
Apply low pass filter on it.
Take a point into consideration only if its x or y values are greater than 0.05 to reduce noise. (Note: The next step depends on your code and on the recognizer you use).
Save x and y points into array.
Create a 2D path from this array.
Send this path to the recognizer to weather train it or recongize it.
Here's my code...
#implementation MainViewController {
double previousLowPassFilteredAccelerationX;
double previousLowPassFilteredAccelerationY;
double previousLowPassFilteredAccelerationZ;
CGPoint position;
int numOfTrainedGestures;
GeometricRecognizer recognizer;
}
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
previousLowPassFilteredAccelerationX = previousLowPassFilteredAccelerationY = previousLowPassFilteredAccelerationZ = 0.0;
recognizer = GeometricRecognizer();
//Note: I let the user train his own gestures, so i start up each time with 0 gestures
numOfTrainedGestures = 0;
}
#define kLowPassFilteringFactor 0.1
#define MOVEMENT_HZ 50
#define NOISE_REDUCTION 0.05
- (IBAction)StartAccelerometer
{
CMMotionManager *motionManager = [CMMotionManager SharedMotionManager];
if ([motionManager isDeviceMotionAvailable])
{
[motionManager setDeviceMotionUpdateInterval:1.0/MOVEMENT_HZ];
[motionManager startDeviceMotionUpdatesToQueue:[NSOperationQueue currentQueue]
withHandler: ^(CMDeviceMotion *motion, NSError *error)
{
CMAcceleration lowpassFilterAcceleration, userAcceleration = motion.userAcceleration;
lowpassFilterAcceleration.x = (userAcceleration.x * kLowPassFilteringFactor) + (previousLowPassFilteredAccelerationX * (1.0 - kLowPassFilteringFactor));
lowpassFilterAcceleration.y = (userAcceleration.y * kLowPassFilteringFactor) + (previousLowPassFilteredAccelerationY * (1.0 - kLowPassFilteringFactor));
lowpassFilterAcceleration.z = (userAcceleration.z * kLowPassFilteringFactor) + (previousLowPassFilteredAccelerationZ * (1.0 - kLowPassFilteringFactor));
if (lowpassFilterAcceleration.x > NOISE_REDUCTION || lowpassFilterAcceleration.y > NOISE_REDUCTION)
[self.points addObject:[NSString stringWithFormat:#"%.2f,%.2f", lowpassFilterAcceleration.x, lowpassFilterAcceleration.y]];
previousLowPassFilteredAccelerationX = lowpassFilterAcceleration.x;
previousLowPassFilteredAccelerationY = lowpassFilterAcceleration.y;
previousLowPassFilteredAccelerationZ = lowpassFilterAcceleration.z;
// Just viewing the points to the user
self.XLabel.text = [NSString stringWithFormat:#"X : %.2f", lowpassFilterAcceleration.x];
self.YLabel.text = [NSString stringWithFormat:#"Y : %.2f", lowpassFilterAcceleration.y];
self.ZLabel.text = [NSString stringWithFormat:#"Z : %.2f", lowpassFilterAcceleration.z];
}];
}
else NSLog(#"DeviceMotion is not available");
}
- (IBAction)StopAccelerometer
{
[[CMMotionManager SharedMotionManager] stopDeviceMotionUpdates];
// View all the points to the user
self.pointsTextView.text = [NSString stringWithFormat:#"%d\n\n%#", self.points.count, [self.points componentsJoinedByString:#"\n"]];
// There must be more that 2 trained gestures because in recognizing, it gets the closest one in distance
if (numOfTrainedGestures > 1) {
Path2D path = [self createPathFromPoints]; // A method to create a 2D path from pointsArray
if (path.size()) {
RecognitionResult recongnitionResult = recognizer.recognize(path);
self.recognitionLabel.text = [NSString stringWithFormat:#"%s Detected with Prob %.2f !", recongnitionResult.name.c_str(),
recongnitionResult.score];
} else self.recognitionLabel.text = #"Not enough points for gesture !";
}
else self.recognitionLabel.text = #"Not enough templates !";
[self releaseAllVariables];
}