09-09-2020, 05:56 AM
A skewed (asymmetrical) calibration grid can negatively affect your data quality / spatial accuracy, so you should always inspect the grid of crosshairs (+) after a calibration.
What to Look For
How to Fix a Skewed Calibration
A poor calibration grid is almost always caused by a suboptimal geometric relationship between the camera, the display monitor, and the participant.
What to Look For
- A Good Calibration: The grid should be well-formed grid in the same pattern presented to the subject. For example, a 9-point calibration should show three roughly parallel horizontal lines and three roughly parallel vertical lines. A slight tilt or a trapezoidal shape is generally acceptable.
- A Problematic Calibration: Significant skew, distortion, or the presence of clear outliers indicates a problem with the physical setup. For example, if the top corners of the grid are stretched too far out, it often means the monitor is too close to the participant or positioned too high.
How to Fix a Skewed Calibration
A poor calibration grid is almost always caused by a suboptimal geometric relationship between the camera, the display monitor, and the participant.
- Adjust Camera Height and Angle
- The camera should be positioned as high as possible without blocking the participant's view of the bottom of the screen. In Remote mode, an improperly placed camera can also make it easier to lose track of the head-tracking sticker if the participant tilts their head.
- For EyeLink 1000 Plus: Adjust the camera height directly on the Desktop mount.
- For EyeLink 1000: You may need to place the Desktop mount on a stand or a stack of books to achieve the proper height.
- For EyeLink Portable Duo Laptop Mount: Adjust the position of the mount over the keyboard and its angle of tilt.
- For EyeLink Portable Duo Tripod Mount: Adjust the length of the tripod legs and the angle of the ball head.
- For EyeLink 1000 Plus: Adjust the camera height directly on the Desktop mount.
- The camera should be positioned as high as possible without blocking the participant's view of the bottom of the screen. In Remote mode, an improperly placed camera can also make it easier to lose track of the head-tracking sticker if the participant tilts their head.
- Adjust Participant and Monitor Position
Ensure the camera is centered with the monitor from the participant's perspective.- For EyeLink 1000 Plus: Center the middle post of the Desktop mount with the monitor.
- For EyeLink 1000: Center the thumb screen, between the camera and illuminator, of the Desktop mount with the monitor.
- For EyeLink Portable Duo: Center the device with the screen.
- For EyeLink 1000 Plus: Center the middle post of the Desktop mount with the monitor.