任意方向上的ios加速度计值

Question

Accelerometer values are provided with respect to the device orientation..

My goal is to get these values irrespective of the device position.

In a considered scenario, if the device is placed in a vehicle, placed face up or horizontally, the accelerometer values along y would indicate the vehicles acceleration.

What if the device is placed in the glove box with random orientation? We can get the roll pitch and yaw values, and convert them into degrees to get the angular displacement of device from the normal face up orientation position but at that random orientation moment, can I get/convert the acceleration values into the the normal face up orientation position values?

Basically what I am following is: get the angular displacement of device -> convert the accelerometer values received at the distorted position to a normal face up orientation position -> get the Y to see the actual acceleration of vehicle irrespective of the device position.

Reference (Point 3.1): http://www.itsasiapacificforum2014.co.nz/files/3314/0194/4873/Abstract_-_Automatic_Accelerometer_Reorientation_for_Driving_Event_Detection_Using_Smartphone_by_Passakon_Prathombutr.pdf

Answer 1

Its quite simple actually, just start generating device motion updates using a reference frame:

- (void)startDeviceMotionUpdatesUsingReferenceFrame:(CMAttitudeReferenceFrame)referenceFrame

Depending on what you want to achieve you can select one of the different options

typedef enum {
   CMAttitudeReferenceFrameXArbitraryZVertical = 1 << 0,
   CMAttitudeReferenceFrameXArbitraryCorrectedZVertical = 1 << 1,
   CMAttitudeReferenceFrameXMagneticNorthZVertical = 1 << 2,
   CMAttitudeReferenceFrameXTrueNorthZVertical = 1 << 3
} CMAttitudeReferenceFrame;

For example, by using "CMAttitudeReferenceFrameXMagneticNorthZVertical" the readings you get from the acceleration would be constant regardless of the device position (they get aligned with "gravity" bellow" and "north" in front). I don't remember the exact reference position but i believe the "top of the phone" points north while the "screen of the phone" points up.