Investigation of Inside-Out Tracking Methods for Six Degrees of Freedom Pose Estimation of a Smartphone in Augmented Reality

Six degrees of freedom (6DoF) input interfaces are essential for manipulating virtual objects through translation or rotation in three-dimensional (3D) space. A traditional outside-in tracking controller requires the installation of expensive hardware in advance. While inside-out tracking controllers have been proposed, they often suffer from limitations such as interaction limited to the tracking range of the sensor (e.g., a sensor on the head-mounted display (HMD)) or the need for pose value modification to function as an input interface (e.g., a sensor on the controller). This study investigates 6DoF pose estimation methods without restricting the tracking range, using a smartphone as a controller in augmented reality (AR) environments. Our approach involves proposing methods for estimating the initial pose of the controller and correcting the pose using an inside-out tracking approach. In addition, seven pose estimation algorithms were presented as candidates depending on the tracking range of the device sensor, the tracking method (e.g., marker recognition, visual-inertial odometry (VIO)), and whether modification of the initial pose is necessary. Through two experiments (discrete and continuous data), the performance of the algorithms was evaluated. The results demonstrate enhanced final pose accuracy achieved by correcting the initial pose. Furthermore, the importance of selecting the tracking algorithm based on the tracking range of the devices and the actual input value of the 3D interaction was emphasized.