Pose estimation in mobile computing systems

An apparatus for determining orientation information, the apparatus comprising:

• at least one memory;
• and
• at least one processor coupled to the at least one memory and configured to:
• determine a pose of a head-mounted device (HMD) according to a six-degrees-of-freedom (6DoF) pose-determination mode of operation, wherein the pose of the HMD comprises a position of the HMD and an orientation of the HMD and wherein the 6DoF pose-determination mode of operation includes processing image data captured at the HMD to determine the pose of the HMD;
• determine that a pose constraint is satisfied based on the determined pose;
• responsive to determining that the pose constraint is satisfied, switch between the 6DoF pose-determination mode of operation and a three-degrees-of-freedom (3DoF) orientation-determination mode of operation;
• and
• determine the orientation of the HMD according to the 3DoF orientation-determination mode of operation, wherein the 3DoF orientation-determination mode of operation includes processing inertial-measurement unit (IMU) data to determine the orientation.