09-07-2020, 05:57 AM
The drift correction offset value is saved in the EyeLink Data File (EDF) for each session. To find this value, you must convert the binary EDF file into a human-readable text file (ASCII).
How to Find the Drift Correction Value
In this example, the measured drift offset was 0.26 degrees. Keep in mind that on modern EyeLink systems (including the EyeLink 1000, 1000 Plus, and Portable Duo), this drift offset is only recorded for your reference by default and is NOT automatically applied to the gaze data. The system's calibration model is not changed by the drift check procedure unless "Apply Correction" is enabled.
How to Find the Drift Correction Value
- Convert the EDF to ASCII. Use the EDF2ASC utility to convert your .edf file into an ASCII (.asc) file. GUI versions of this tool are included with our Data Viewer software (Windows) or Developers Kit (macOS) and does not require a license.
- Open and Search the File. Open the new text file in any text editor and search for the term "DRIFTCORRECT". You will find a message line that looks like this:
Code:MSG 8546331 DRIFTCORRECT R RIGHT at 512,384 OFFSET 0.26 deg
In this example, the measured drift offset was 0.26 degrees. Keep in mind that on modern EyeLink systems (including the EyeLink 1000, 1000 Plus, and Portable Duo), this drift offset is only recorded for your reference by default and is NOT automatically applied to the gaze data. The system's calibration model is not changed by the drift check procedure unless "Apply Correction" is enabled.