What does Core Motion error 102 mean?

Question

I use Core Motion's sensor fusing to get north oriented motion updates:

[motionManager startDeviceMotionUpdatesUsingReferenceFrame:CMAttitudeReferenceFrameXTrueNorthZVertical toQueue:motionQueue withHandler:motionHandler]

In a very rare case that can be reproduced only on selected customer devices (iPhone 4S running iOS 6.0.2) I receive this error in the motionHandler:

Error Domain=CMErrorDomain Code=102 "The operation couldn’t be completed. (CMErrorDomain error 102.)

Also, it seems I don't get any valid deviceMotion updates after that. Does anybody know what this error 102 means? I can't find anything in the documentation.

Answer 1

As Krishnabhadra correctly pointed out, this error code means CMErrorTrueNorthNotAvailable. The description ("True north is not available on this device. This usually indicates that the device’s location is not yet available.") unfortunately doesn't give any hint how to solve the issue so I'd like to describe my findings when this error occurs.

It occurs on a tiny (a handful out of many thousands) fraction of iOS 6.0+ devices when using CMAttitudeReferenceFrameXTrueNorthZVertical (CMAttitudeReferenceFrameXMagneticNorthZVertical is OK). Despite the error description, Core Location works correctly. On affected devices the bug is triggered in 100% of the cases and blocks Core Motion updates completely. -[CMMotionManager deviceMotion] always returns nil.

Resetting the iOS system settings fixes the problem.

I’ve logged rdar://12952327 with some more details.

Update: This error occurs if compass calibration is disabled in the privacy / location services / system services section.

Answer 2

From documentation

typedef enum {
   CMErrorNULL = 100,
   CMErrorDeviceRequiresMovement,
   CMErrorTrueNorthNotAvailable
} CMError;

It seems error 102 is CMErrorTrueNorthNotAvailable, and its description is

CMErrorTrueNorthNotAvailable

It seems not much information is available regarding what causes this error. It can be any hardware issue with the device.

Answer 3

Also, make sure this is enabled. After I enabled this option, I did not encounter the 102 issue anymore while using xTrueNorthZVertical.

Settings > Privacy > Location Services > System Services > Compass Calibration