问CMAttitudeReferenceFrameXTrueNorthZVertical不指向北方

EN

        [self.motionManager startDeviceMotionUpdatesUsingReferenceFrame:CMAttitudeReferenceFrameXTrueNorthZVertical toQueue:[NSOperationQueue currentQueue]
                                                   withHandler: ^(CMDeviceMotion *motion, NSError *error){
                                                       [self performSelectorOnMainThread:@selector(handleDeviceMotion:) withObject:motion waitUntilDone:YES];
                                                   }];
    }
}

- (void)handleDeviceMotion:(CMDeviceMotion*)motion {
   CMAttitude *attitude = motion.attitude;
   double yaw = attitude.yaw * 180 / M_PI;
   double pitch = attitude.pitch * 180 / M_PI;
   double roll = attitude.roll * 180 / M_PI;
   self.xLabel.text = [NSString stringWithFormat:@"%7.4f", yaw];
   self.yLabel.text = [NSString stringWithFormat:@"%7.4f", pitch];
   self.zLabel.text = [NSString stringWithFormat:@"%7.4f", roll];
   [self sendDeviceAttitudeLogWithYaw:yaw pitch:pitch roll:roll];
}