The Camera Setup node in current versions of Experiment Builder has several properties that allow you to alter the location of the calibration and validation targets.
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 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).
- Calibration / Validation Area Proportion Properties
By default, calibration and validation targets are presented in a rectangle that covers 88% of the screen horizontally and 83% vertically. These default values are used if the properties are set to 0,0. You can change the proportion of the screen used for calibration and validation targets separately, by inputing a pair of values between 0.2 and 1.0 to the relevant properties (for example 0.8,0.8).
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 (for example if your display screen has to be closer than the recommended distance).
- Calibration / Validation Corner Scaling Properties (9- and 13-Point Calibrations Only)
This property controls the distance of the corner targets from the screen center. Values less than 1.0 will bring the corner targets towards the center, creating a more elliptical pattern, which can be helpful when viewing the calibration through a cylindrical viewport, such as in MRI environments. The minimum value is 0.5.
The validation corner scaling value should be slightly smaller than the calibration corner scaling value, to ensure a more robust test of the calibration model. By default, calibration corner scaling is 1.0 and validation corner scaling is 0.88. These default values will be used if the properties are set to 0.
Note: These properties can be used in combination with the rescaling properties described above.
- Enable Customized Calibration / Validation Positions Properties
For complete control, you can define your own list of X, Y coordinate pairs for each calibration / validation target. The target points must be defined in a specific order, and there are constraints about the positioning of the targets relative to one another. For detailed instructions and the correct point order for each model, please consult the Experiment Builder Manual (Help menu > Contents > Components > Actions > Performing Camera Setup and Calibration).
Note: If these properties are checked, the scaling and corner correction properties are not available.