305
A Test Environment for Studying Robotic Eye Movements
a forward-facing, wide-angled scene camera operating in the near-infrared
spectrum. The wizard’s screen has five infrared light-emitting diodes (LEDs)
arranged in a predefined geometrical setup. These LEDs are detected by the
eye tracker’s calibrated scene camera, so it is possible to calculate the goggles’
position and with it the head pose.
After a simple calibration procedure, which requires the subject to fixate
on five different calibration targets projected by a head-fixed laser, the eye
tracker yields eye directions in degrees. The fixation points are generated by
a diffraction grating at equidistant angles, regardless of the distance to the
projection. Because at small distances a parallax error would be generated
by the offset between eye and calibration laser, the laser dots are projected
to a distant wall. At a typical distance of 5 meters, the error decreases to
0.4 degrees. In view of the refixation accuracy of the human eye of about 1
degrees (Eggert 2007), this is a tolerable value.
In an additional step, the wizard’s origin of gaze, that is, the center of the
eyeballs, with respect to the head coordinate system, has to be calculated.
This is done by letting the wizard fixate on two known points on the screen
without moving his head. The results are two gaze vectors per eye from
which the eyeball center can be calculated in head coordinates. After complete calibration, the point of gaze in the screen plane can be determined
together with the head pose.
During normal operation, the wizard is shown two markers on his screen
as a feedback. The calculated eye position is displayed together with the
intersection of the head direction vector and the screen plane. This is used
to validate the calibration during the experiment. Furthermore, the wizard
has better control over the robot, because he sees where the robot’s head
points to.
Depending on the robot’s capabilities two, respectively five, head angles
plus two eye angles for each eye are sent.
In the Results section we will report on the accuracy, resolution, and
real-time capable delays that we achieved with this eye tracker.
16.2.4 Teleoperation Channel
The robot head (see Figure 16.1) is equipped with a forward-facing, wide-angle
camera mounted on the neck. The camera is tilted slightly upwards to point
to the face level of humans in front of the robot. The image of the scene camera is displayed on the wizard’s video monitor.
To keep the latency low, we decided to use two different transmission
channels: a USB connection for the eye and head position signals and standard analog video equipment for the scene view, consisting of an analog
video camera and a CRT video monitor, both operating at a 50 Hz PAL
frame rate.
A Test Environment for Studying Robotic Eye Movements
a forward-facing, wide-angled scene camera operating in the near-infrared
spectrum. The wizard’s screen has five infrared light-emitting diodes (LEDs)
arranged in a predefined geometrical setup. These LEDs are detected by the
eye tracker’s calibrated scene camera, so it is possible to calculate the goggles’
position and with it the head pose.
After a simple calibration procedure, which requires the subject to fixate
on five different calibration targets projected by a head-fixed laser, the eye
tracker yields eye directions in degrees. The fixation points are generated by
a diffraction grating at equidistant angles, regardless of the distance to the
projection. Because at small distances a parallax error would be generated
by the offset between eye and calibration laser, the laser dots are projected
to a distant wall. At a typical distance of 5 meters, the error decreases to
0.4 degrees. In view of the refixation accuracy of the human eye of about 1
degrees (Eggert 2007), this is a tolerable value.
In an additional step, the wizard’s origin of gaze, that is, the center of the
eyeballs, with respect to the head coordinate system, has to be calculated.
This is done by letting the wizard fixate on two known points on the screen
without moving his head. The results are two gaze vectors per eye from
which the eyeball center can be calculated in head coordinates. After complete calibration, the point of gaze in the screen plane can be determined
together with the head pose.
During normal operation, the wizard is shown two markers on his screen
as a feedback. The calculated eye position is displayed together with the
intersection of the head direction vector and the screen plane. This is used
to validate the calibration during the experiment. Furthermore, the wizard
has better control over the robot, because he sees where the robot’s head
points to.
Depending on the robot’s capabilities two, respectively five, head angles
plus two eye angles for each eye are sent.
In the Results section we will report on the accuracy, resolution, and
real-time capable delays that we achieved with this eye tracker.
16.2.4 Teleoperation Channel
The robot head (see Figure 16.1) is equipped with a forward-facing, wide-angle
camera mounted on the neck. The camera is tilted slightly upwards to point
to the face level of humans in front of the robot. The image of the scene camera is displayed on the wizard’s video monitor.
To keep the latency low, we decided to use two different transmission
channels: a USB connection for the eye and head position signals and standard analog video equipment for the scene view, consisting of an analog
video camera and a CRT video monitor, both operating at a 50 Hz PAL
frame rate.