Do I need to use NSTimer to get data from gyroscope iOS?

Question

Right now I'm using the following code to get Euler values from the device's gyroscope. Is this how it's supposed to be used? Or is there a better way without using NSTimer?

- (void)viewDidLoad {
[super viewDidLoad];
CMMotionManager *motionManger = [[CMMotionManager alloc] init];
[motionManger startDeviceMotionUpdates];

NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:(1/6) target:self selector:@selector(read) userInfo:nil repeats:YES];
}

- (void)read {
CMAttitude *attitude;
CMDeviceMotion *motion = motionManger.deviceMotion;
attitude = motion.attitude;
int yaw = attitude.yaw; 
}

My goal is to continuously monitor the yaw value to determine if the device has rotated 360 degrees along its center. What's the most efficient way to do this? — thisiscrazy4, Dec 21 '12 at 06:43

score 1 · Answer 1 · answered Dec 21 '12 at 06:42

You Can Use This...

    [motionManager startDeviceMotionUpdatesToQueue:[NSOperationQueue currentQueue] withHandler:^(CMDeviceMotion *motion, NSError *error)
 {
     CMAttitude *attitude;
     attitude = motion.attitude;
     int yaw = attitude.yaw; 
 }];

score 0 · Answer 2 · answered Dec 21 '12 at 06:42

Directly to quote the documentation:

Handling Motion Updates at Specified Intervals

To receive motion data at specific intervals, the app calls a “start” method that takes an operation queue (instance of NSOperationQueue) and a block handler of a specific type for processing those updates. The motion data is passed into the block handler. The frequency of updates is determined by the value of an “interval” property.

[...]

Device motion. Set the deviceMotionUpdateInterval property to specify an update interval. Call the or startDeviceMotionUpdatesUsingReferenceFrame:toQueue:withHandler: or startDeviceMotionUpdatesToQueue:withHandler: method, passing in a block of type CMDeviceMotionHandler. With the former method (new in iOS 5.0), you can specify a reference frame to be used for the attitude estimates. Rotation-rate data is passed into the block as CMDeviceMotion objects.

So e.g.

motionManger.deviceMotionUpdateInterval = 1.0/6.0; // not 1/6; 1/6 = 0
[motionManager 
    startDeviceMotionUpdatesToQueue:[NSOperationQueue mainQueue]
    withHandler:
        ^(CMDeviceMotion *motion, NSError *error)
         {
             CMAttitude *attitude;
             attitude = motion.attitude;
             int yaw = attitude.yaw; 
         }];

I've lazily just used the main queue but that still may be a better solution than the NSTimer because it'll give the motion manager an explicit clue about how often you care to be updated.

Do I need to use NSTimer to get data from gyroscope iOS?

2 Answers2