# The Effects of Augmented Reality Interaction Techniques on Egocentric Distance Estimation Accuracy
## 2 Methods
### Experimental Settings and Stimuli  
The VE, the 3D stereoscopic targets, and the experimental task were developed in Unity 3D (version 4.3.4f1). The VE was projected by a ViewSonic 3D projector and the task ran on a high-speed computer that supported stereoscopic vision (processor Intel Core-i7-7700 CPU @3.60 GHz, with installed RAM 8 GB, and NVIDIA GeForce GTX 1060 6 GB graphics); the latency of the virtual system could be minimized such that it should not affect the performance of interaction. To perceive the 3D stereoscopic targets at three different egocentric distances, participants wore NVIDIA 3D glasses integrated with a 3D vision emitter. The parallax was adjusted based on the required egocentric distances (90 cm, 120 cm, or 150 cm from the participant) and the interpupillary distance (IPD) of each participant. The interaction by direct pointing was performed using light wooden sticks of three different lengths, 80 cm, 110 cm, and 140 cm, with 0.6 cm reflective markers attached to their tips. The material of the pointing stick was carefully chosen to minimize the adverse effects of its weight on the participants' pointing postures or performance. The data of the reflective marker positions were recorded and tracked by a 6D motion capture system (Optitrack) at a frame rate of 120 frames per second. To confirm the pointing actions, participants had to click a Logitech spotlight wireless remote attached at the lower end of the stick. The interaction by indirect cursor was performed using a gamepad, a Sun-Yes R-0011 dual analog. The gamepad analog enabled the movement of the cursor along the x-, y-, and z-axes within the VE. The left analog of the gamepad controlled a virtual cursor in two-degrees-of-freedom (DoF) of translation (up and down, left and right), including diagonal movement, while the right analog of the gamepad controlled the depth (forward and backward) of the virtual cursor. The size of the virtual cursor was scaled to approximately the width of each target to provide good visualization when touching the target. Four programmable buttons were located on the gamepad grip, but for this study, only the primary button \"X\" was activated (to confirm the pointing). Greater force on the gamepad analog increased the velocity of the virtual cursor. We optimized the sensitivity value of the gamepad between the exerted force and the cursor speed. A preliminary experiment was conducted to obtain an optimum sensitivity value to control the cursor to a comfortable condition for precise and fast movement. The average value was approximately 2 m/s, and we used this value for subsequent experiments. The starting points of the stick tips and virtual cursors were kept fixed at three different positions, P\({}_{1}\), P\({}_{2}\), and P\({}_{3}\), marked on the table (as shown in Figure 3). Considering the projector as a reference of measurement, the relative positions of the initial positions of the tips and cursors were P\({}_{1}\) (82, 0, 82), P\({}_{2}\) (82, 0, 90), and P\({}_{3}\) (82, 0, 120) for targets at egocentric distances of 90, 120, and 150 cm, respectively. For each trial, both the stick tip and the cursor position were restarted at the initial positions. The data streams from the marker position, virtual cursor, and virtual target were collected and processed by PC to analyze how close the estimates of the egocentric distance were to the reference of the theoretical positions. To minimize the possibility of differences in the perceived egocentric distances because of the head motions, the participants rested their chins on a fixed chinrest on the tabletop and sat on an adjustable chair to ensure consistency in height.