FAQ: How can I change the calibration / validation target locations?

[SR-SUPPORT]

There are three methods that can be used to change the size and shape of the calibration area.

1. Rescale the entire calibration area.
   
   By default calibration and validation targets are presented in a rectangle that subtends 88% of the screen horizontally and 83% vertically. These values can be altered by using two EL_COMMAND nodes at the start of the project with the following commands:
   
   
   Code:

   Command= calibration_area_proportion
Text = 0.88 0.88
   
   
      
   
   
   Code:

   Command = validation_area_proportion
Text = 0.88 0.88
   
   
      
   
   The two values correspond to the desired proportion of the X and Y dimensions of the screen used for the calibration area. We have a handy online Calibration Coordinate Calculator which given the screen measurements, resolution, and eye to screen distance value, can provide appropriate calibration proportion values. 
   Please note that it is generally not a sensible idea to calibrate only a small area of the screen (even if stimuli are only presented in a small area), the calibration targets should only be shifted if they are unable to be seen by the participant (for example, a large monitor is too close to the participant to calibrate the entire screen). 
   
   
2. Alter the location of the corner targets (for 9 and 13 point calibrations only).
   
   To do this use two EL_COMMAND nodes at the start of the experiment with the following commands:
   
   
   Code:

   Command = calibration_corner_scaling
Text = 0.88
   
   
      
   
   
   Code:

   Command = validation_corner_scaling
Text = 0.88
   
   
      
   
   The value will scale the corners in a given percentage of the overall screen to make more of an elliptical calibration pattern.
   This can be particularly helpful in MRI environments. Also, note that the validation_corner_scaling value should be slightly less than the calibration value to give the validation process a slightly more robust test of the model by using different gaze locations than the original calibration.
   
   
3. Create your own custom target locations using the "Enable Customized Calibration Positions" of the CAMERA_SETUP node.
   
   This requires a list of screen points in a very specific order, depending on the chosen calibration model (HV5, HV9, etc...). Please see the Experiment Builder Manual (Help menu -> Contents) for further details (Components -> Actions -> Performing Camera Setup and Calibration).