FAQ: Can I change the location of the calibration targets during the calibration routine?

[Sam]

Please Note:

• Calibration and Validation target locations should only be altered if the participant cannot see them in their default locations, or if the default calibration area exceeds the trackable range of the system (for example if your screen is too close and cannot be moved further back).
  
• If you reduce the calibrated area, it is important that any stimuli you present fit within the reduced calibrated area.
  
• Calibrating a relatively small area of the screen, even if your stimuli are small and confined to that area, will inevitably result in poorer spatial accuracy than calibrating to a larger proportion of the screen, so should be avoided.
  
• If custom target locations are used, it is critical that the new locations maintain the spatial arrangement of the original calibration model (e.g. a 3x3 grid for the HV9 calibration / a cross shape for the HV5 calibration).
  

There are two primary methods for adjusting the calibration and validation target locations:

• Option 1:
  This method allows you to change the overall horizontal and vertical proportion of the display screen used for calibration and validation. You can implement this by either:
  • Copying the parameters below to the FINAL.INI file on the Host PC (see footnote for instructions on accessing .INI files).
    
  • Sending commands via your experimental script.
    
  Code:

  calibration_area_proportion 0.88 0.83
validation_area_proportion 0.88 0.83
  In the above parameters, the first value represents the horizontal proportion of the screen used, and the second value represents the vertical proportion. The values 0.88 and 0.83 are the default settings.
  
  To determine appropriate proportion values based on your stimuli, screen size and eye-to-screen distance, you can use our handy online Calibration Coordinate Calculator.
  
  
• Option 2:
  
  Alternatively, each calibration / validation target can be precisely specified in pixel coordinates (see notes below about screen origin). To achieve this, specific parameters need to be modified on the Host PC. These parameters should be specified in the FINAL.INI file (see footnote for file location) or by sending commands via your experimental script (e.g., Experiment Builder, Psychtoolbox, E-Prime, etc.) before entering Camera Setup mode.
  
  Note that the full syntax of these commands can be referenced in the CALIBRI.INI, but please do not alter the values in this file as they my get overwritten by future host software upgrades and alterations. All custom commands should be saved into the FINAL.INI, or simply sent by your experimental script.
  • First, disable default targets:
    
    Code:

        ## generate_default_targets = <YES or NO>
    ;; YES = Default targets and sequence are enabled for calibration and validation
    ;; NO = Default targets will be DISABLED and custom targets positions must be specified.
generate_default_targets = NO
    
    
  • Then, the pixel coordinates for each target position must be specified as x,y pairs (pixel positions must be specified assuming the top-left corner of the Display PC as [0, 0] and bottom right corner is the maximum resolution of your display):
    
    Code:

        ## calibration_targets = <list of x,y coordinate pairs>
    ;; X,Y pairs of target point positions.
calibration_targets = 320,240 320,40 320,440 40,240 600,240 40,40 600,40, 40,440 600,440
    ## validation_targets = <list of x,y coordinate pairs>
    ;; X,Y pairs of validation target positions.
validation_targets = 320,240 320,40 320,440 40,240 600,240 40,40 600,40, 40,440 600,440
    
    IMPORTANT NOTE - Each parameter contains a set of X,Y pixel coordinate pairs. While you can specify different values, it is crucial to preserve the ordering for the pattern as outlined below::
    
    Code:

    ## calibration_targets = <list of x,y coordinate pairs>
;; X,Y pairs of target point positions
;; these are in display coordinates

;; FOR 9-POINT ALGORITHM:
;; POINTS MUST BE ORDERED ON SCREEN:
;; 6   2   7
;; 4   1   5
;; 8   3   9 

;; FOR 13-POINT ALGORITHM:
;; POINTS MUST BE ORDERED ON SCREEN:
;; 6        2      7
;;     10     11
;; 4       1       5
;;    12     13
;; 8       3       9
    
    
  • Experiment Builder Specific Recommendation:
    If you are using Experiment Builder, it is highly recommended to use the built-in properties of the Camera Setup node for customizing calibration and validation positions, rather than manually editing the FINAL.INI file. Please see the following FAQ:
    
    How can I change the calibration / validation target locations in Experiment Builder?
    
    

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Both the CALIBRI.INI and FINAL.INI files are located in the /ELCL/EXE/ folder within the EyeLink partition on the Host PC.

• EyeLink 1000 Plus and EyeLink Portable Duo: These files can be edited via the file manager software on the Host PC.
  
• EyeLink II and EyeLink 1000: You will need to boot the Host PC to Windows to edit these files (the EyeLink partition will appear as another drive).