iPhone/iPad gyroscope

I never re开发者_Go百科ally understand the applications of the gyroscope on the iPhone/iPad, does it serve the similar function as the accelerometer but like an improvement to the accelerometer? What is the practical use of it?

"An accelerometer is a direct measurement of orientation, while a gyro is a measurement of the time rate of change of orientation." (1)
By combing the output of the two sensors, called sensor fusion, one can determine the orientation of the device precisely and fast. If you only use accelerometer with a low-pass filter, you still get a reasonable estimate for the orientation but it will lag.

Here is an excellent live demo of both (Google Tech Talk), starting at 21:50.

Gyroscope measures orientation, where accelerometer measures movement. Both have useful applications (gyroscope: Which direction am I driving towards? Accelerometer: Did I just shake my device?)

The accelerometer tells you the difference in the force being experienced by the device and the force it would experience if it were in free fall. So if the device is static, the accelerometer tells you which way up is. When it's being shaken around, you get a summation of up plus the direction of the shake. Hence the accelerometer can detect some rotation, but not around the gravity vector and only if the device is otherwise static.

The gyroscope tells you the velocity at which the device is being rotated. So you can integrate values coming from it to keep track of orientation. That works across all axes and irrespective of device movement.