In a previous work we evaluated the gaze mapping accuracy within 3D scene environments using a novel 3D-Eye-Tracker.
17 For this study, we used this 3D-Eye-Tracker to acquire participants' dioptric demand in spatiotemporally diverse ecological environments. The 3D-Eye-Tracker combines head-mounted eye-tracking (Core–binocular; Pupil Labs GmbH, Berlin, Germany)
20,21 and time-of-flight camera technology (Pico Flexx; PMD Technologies AG, Siegen, Germany)
22 to map gaze estimates onto 3D point clouds taken from the participant's vantage point. To record eye-tracking data, Pupil Labs’ open-source software package “Pupil” was used (PLPupil, version 1.21-5). A custom software plugin was developed to temporally align the 3D point cloud with PLPupil's eye-tracking data (Pico Flexx Depth Plugin–Backend version: f24533a, Plugin version: 0fd0b3f).
23 Mapped gaze estimates were determined from high-speed eye cameras (120Hz binocular) within a 0.11 ± 2.4 milliseconds window of point-cloud acquisition. For gaze estimation, PLPupil's 3D eye-model mode was used since it compensates for slippage
24—the undesirable but common displacement of the head-mounted eye-trackers relative to the eye(s). The long-term accuracy for gaze mapping has been found to be maintained within 3.6° for the entire field of view of the Pico Flexx.
17 Pico Flexx records a point cloud, which contains the spatial scene information, with a visual field of 62° horizontal and 45˚ vertical/224 × 171pixels (for each pixel, a distance-vector is recorded with x, y, and z coordinates)/0.28° × 0.26° resolution, respectively. On average, five point clouds were acquired per second, with each at an acquisition time of approximately 30 milliseconds.
22 Before measurements were taken, the 3D-Eye-Tracker needed to be adjusted according to instructions from the manufacturer.
25 The field of view of the 3D-Eye-Tracker's scene camera was aligned with the anticipated range of the regions of interest for attentional capture during the study. With a habitual head position, the field of view of the Pico Flexx comprised the horizontal line of vision as an upper extreme and the direct view onto hand-held devices as a lower extreme (because they are positioned habitually much lower than the horizontal line of vision). The 3D-Eye-Tracker established a 3D model of each eye including nominal gaze direction from the eye-camera images.
24,26 These gaze direction estimates were aligned with the point cloud during a five-point calibration process as described previously.
17,27