Jerk or throw motion detection with iphone - iphone

Question

I am making a stone throw app that shows a rock skipping over water. What I want do to is detect a motion when the hand moves quickly from side to the front (like as if you were skipping rocks). I tried the following code and this is the results I get in my log. Is there a gesture detection that I can use?
-(void)motionEnded:(UIEventSubtype)motion withEvent:(UIEvent *)event
{
if (event.subtype == UIEventSubtypeEndSeekingForward)
{
NSLog(#" Forward event ...");
}
else
{
NSLog(#" Something moved but I dont know what event ...");
}
if ([super respondsToSelector:#selector(motionEnded:withEvent:)])
[super motionEnded:motion withEvent:event];
}
-(BOOL)canBecomeFirstResponder
{
return YES;
}
-(void) viewWillAppear:(BOOL)animated
{
[self becomeFirstResponder];
[super viewWillAppear:animated];
}
- (void) viewWillDisappear:(BOOL)animated
{
[self resignFirstResponder];
[super viewWillDisappear:animated];
}
This is what I get when I quickly move my iPhone back and forth (happens both ways)
Something moved but I dont know what event ...
Something moved but I dont know what event ...
Something moved but I dont know what event ...
Also, I had to put a lot of force to make the detection work. So two questions
Is there some built in threshold number that I can override?
And how can I tell it to do this action only when phone is moved forward?
Thanks

Answer 1

If you see the class reference for UIEvent, you'll realize that the only motion related event subtype is UIEventSubtypeMotionShake, which means you can only know, from that event, that the device was shaken.
To achieve what you want to achieve, you would have to use accelerometer values directly.
This means that, first, you would have to do some tests on what values the accelerometer returns when you are doing that specific movement, and on different steps of the movement. You also have to get the range of values in which the movement still makes sense.
Then, you will need to integrate those values into your app, basically, what you'd have to do, is, in your accelerometer delegate, to check that, in every step of the movement, the values the accelerometer is giving you are inside the ranges that you tested make sense.
It's not gonna be a walk in the park, be advised.