CMDeviceMotion userAcceleration漂移 [英] CMDeviceMotion userAcceleration drift

问题描述

我使用获取加速度数据 - [CMDeviceMotion userAcceleration]

我注意到了一个有趣的是：我总是在Z轴上得到一个小偏差。它约为0.0155（方差为0.002）。在其他轴上，平均值接近0。

I've noticed one interesting thing: I always get a small bias on the Z axis. It is about 0.0155 (with variance of 0.002). While on other axes the average values are near 0.

我正在使用iPod Touch 4G进行测试（测试期间它只是放在桌子上）。问题是：这个偏差来自哪里？它是特定于设备的？

I'm testing this with iPod Touch 4G (and it is just laying on the table during testing). The question is: where this bias is from and is it device specific?

推荐答案

我注意到类似的值，尽管CoreMotion试图消除偏见。如果旋转设备使x（或y）与重力平行，则可能会看到x方向的偏差。使用原始传感器数据显示了相同的趋势，但具有更大的值和一些更强大的效果，如温度依赖性，基于时间的移位，...

I noticed similar values although CoreMotion tries to eliminate bias. If you rotate your device so that x (or y) is parallele to gravity you will probably see the bias in x direction. Using raw sensor data showed the same tendency but with larger values and some more super-imposing effects like temperature dependency, time based shifting, ...

18个月前我读过iPhone 3设备的加速度计的规格，据此，准确度约为g的1.8％。 （可惜我现在设置的STM产品页面的书签导致404）。

18 months ago I read a specification of the iPhone 3 devices' accelerometers and according to this the accuracy was about 1.8 % of g. (what a pity the bookmark to STM product page I set now leads to 404).

基本上这不应该是一个问题，只要你不试图估计准确的位置（位移），这似乎是不可能的，具有可接受的准确性 - 请参见SO上的几个讨论。

Basically this should not be a problem as long as you don't try to estimate exact positions (displacements) and this seems to be impossible with an acceptable accuracy - see the several discusion here on SO.

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