User manual

124 Appendix A: Using the EyeLink 1000 Analog and Digital Output Card

ANALOG.INI). This allows operation with binocular data when few analog inputs

are available, and when pupil size data is not required. The results of all

combinations of configurations and monocular/binocular eye tracking modes

are summarized in the table below, with X and Y representing horizontal and

vertical position data, and P representing pupil size data.

7.4.2 Analog Data Types and Ranges

Both gaze and HREF position data are available for analog output. These are

selectable through the EyeLink 1000 tracker's Set Options menu screen. Each

of these is scaled to a voltage on the analog output as described below. Raw

pupil (or pupil-CR) data is also available for applications that implement their

own calibrations.

7.4.3 Scaling of Analog Position Data

Each of the types of position data is scaled to match the selected analog output

voltage range. Several variables in ANALOG.INI set what proportion of the

expected data range for each type will be represented at the output, and what

the total voltage range will be.

• Total analog voltage range is set by analog_dac_range, followed by the

highest and lowest voltage required. The voltage range may be from -10 to

+10 volts, with other typical ranges being -5 to +5, or 0 to +10 volts.

• The fraction of the total data range to be covered is set by the

analog_x_range and analog_y_range variables. These are followed by the

data type, and the minimum and maximum range fraction. For example, 0

to 1.0 would cover the full range of the data, 0.1 to 0.9 would cover the

central 80% of the data, and -0.2 to 1.2 would add a 20% margin above and

below the expected data range.

• For raw data, the default range is 0.1 to 0.9, because the pupil position will

never reach the edges of the camera image. It is possible that the scaled and

transformed pupil-CR data might exceed this range, but in general this

range will be similar to that of the camera image. Raw data should be

assumed to be in arbitrary units.

For HREF data, the entire data range is assumed to be -30000 to +30000. This

is about 127°. This should never be exceeded. The default range setting is

therefore 0.0 to 1.0. The HREF data may be recovered from the voltage by the

following formula:

HREF = (voltage-(minvoltage+maxvoltage/2)*60000/(maxvoltage-minvoltage)