The coordinate system's y-axis is parallel to gravity, its x- and z-axes are oriented to compass heading, and its origin is the initial position of the device.
- iOS 11.0+
The y-axis matches the direction of gravity as detected by the device's motion sensing hardware; that is, the vector
(0,-1,0) points downward.
The x- and z-axes match the longitude and latitude directions as measured by Location Services. The vector
(0,0,-1) points to true north and the vector
(-1,0,0) points west. (That is, the positive x-, y-, and z-axes point east, up, and south, respectively.)
Although this option fixes the directions of the three coordinate axes to real-world directions, the location of the coordinate system's origin is still relative to the device, matching the device's position as of when the session configuration is first run.