FAQ: How do I tell the system how far the camera is from the screen? Why is this needed?
In order to accurately compute eye velocity and saccade amplitude in degrees of visual angle, the Host PC software needs to know the distance of the eye to the screen, as well as the screens physical dimensions (see our Visual Angle blog post).

When using either the EyeLink 1000, EyeLink 1000 Plus, or EyeLink Portable Duo in head-stabilized mode, the distance from the eye to screen is specified using the screen_distance parameter (or the Eye-to-Screen Distance setting in the EyeLink 1000 Plus or EyeLink Portable Duo's Screen Settings page). In Remote mode, the tracker calculates the eye-to-camera distance for each sample based on the size of the head target sticker in the camera image. Therefore, in order to accurately calculate the eye-to-screen viewing distance in Remote Mode, the Host software needs to also know the distance of the eye tracker relative to the screen (because the screen-to-camera distance plus camera-to-eye distance equals screen-to-eye distance). In order to set the screen-to-camera distance please follow the steps below:

For the EyeLink 1000 Plus or EyeLink Portable Duo:

To set the screen_distance parameter, quit the host software to the File Manager (CTRL+ALT+Q), go to the Configuration page by clicking the cogwheel icon, then go to Screen Settings, and select Camera-to-Screen Distance. Here you can enter the distance camera-to-screen distance necessary for remote mode operation. For the EyeLink 1000, this is the distance from the front of the screen to the point where the lens connects to the camera. For the EyeLink Portable Duo, this would be the distance from the back of the camera case to the front of the screen. Once entered, click “Save” to apply the value.


For the EyeLink 1000:

Go into the Windows partition of the Host PC and add the "remote_camera_position" command to the FINAL.INI file in the /ELCL/EXE/ folder:

// remote_camera_position <rh> <rv> <dx> <dy> <dz>
remote_camera_position 10 17 -80 60 -90

The first four arguments in this function are fixed and camera-specific so they should not be altered. The last argument (<dz>) in the code above corresponds to the distance of the camera to the screen in millimeters and is the only parameter that needs to be modified for remote mode configurations. To get the appropriate value for your setup, measure the distance between the base of the camera lens (at the point where the lens connects to the camera) to the Display monitor, e.g. if the distance is 190 mm, set the remote_camera_position to “10 17 -80 60 -190”, make sure that there is a "-" sign before final parameter. Copy the updated setting to the FINAL.INI file, or send the command within the experiment script after initializing a connection to the Host PC.