iPhone/iPad 陀螺仪
我一直不太了解陀螺仪在iPhone/iPad上的应用，它是否具有与加速度计类似的功能，但像是对加速度计的改进？它的实际用途是什么？
I never really 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?
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“加速度计是方向的直接测量，而陀螺仪是方向变化的时间速率的测量。” (1)
通过组合两个传感器的输出（称为传感器融合），人们可以精确、快速地确定设备的方向。
如果您仅使用带有低通滤波器的加速度计，您仍然可以获得对方向的合理估计，但它会滞后。
这是精彩的现场演示（Google 技术讲座），将于 21:50 开始。
"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.
陀螺仪测量方向，加速计测量运动。两者都有有用的应用（陀螺仪：我正在朝哪个方向行驶？加速计：我刚刚摇动了我的设备吗？）
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?)
加速度计会告诉您设备所承受的力与自由落体时所承受的力的差异。因此，如果设备是静态的，加速度计会告诉您向上的方向。当它被晃动时，你会得到向上的总和加上晃动的方向。因此，加速度计可以检测到一些旋转，但不能检测到围绕重力矢量的旋转，并且仅当设备处于静止状态时。
陀螺仪告诉您设备旋转的速度。因此您可以整合来自它的值来跟踪方向。这适用于所有轴，并且与设备移动无关。
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.