Calibrate Dikablis eye tracking in Vicon Nexus

Before capturing an eye tracking trial, you must calibrate eye tracking within Nexus.

To do this, complete the following procedures in the order shown.

Set up a calibration trial for eye-tracking

To set up a Vicon Nexus calibration trial for eye-tracking:

1. Before you begin a calibration trial for eye-tracking, ensure you have calibrated your Vicon cameras, set the volume origin, and added the Dikablis device to Nexus.
2. Get your subject to enter the volume wearing the head unit with markers, and holding the calibration wand in front of them.
3. In the Capture tools pane, in the Next Trial Setup section, enter a Trial Name (for example, Calibration), and in the Capture section, click Start to capture a short trial (a couple of seconds).

4. Load the trial you just created (on the Data Management tab (F2), double-click on the trial) and on the Nexus toolbar, click the Reconstruct button .

5. In 3D Perspective view, zoom in so you can see the two objects (subject and wand).

   

Create objects for eye tracking in Vicon Nexus

To set up a calibration trial for eye tracking, you need to create wand and head objects.

To create the objects in Nexus:

1. On the Subjects resources pane, click the Create a blank subject button.

   

2. In the Enter Subject Name dialog box, enter the subject name: Wand.
3. On the Subjects tab, click the Wand object you just created to select it and at the top of the Subject Preparation tools pane on the right of the screen, in the Subject dropdown menu, ensure Wand is selected.
4. In the Subject Preparation tools pane, in the Labeling Template Builder section, enter a segment name (Wand) in the Create Segments box and click Create.

   

5. In a 3D Perspective view, select the wand markers, beginning with the origin (middle) marker.

   

6. Ensure all the wand markers are selected.

   

7. In the Labeling Template Builder section, click Create again.
8. In the 3D Perspective view, check the axes and origin are shown for the wand.

   

9. To create a head object, in the Subjects Resources pane, click the Create a blank subject button and in the Enter Subject Name dialog box, enter Head.
10. On the Subjects resources pane, click the Head object you just created and at the top of the Subject Preparation tools pane, ensure Head is selected.
11. In the Labeling Template Builder section, in the Create Segments box, type Head and click Create.
12. In the 3D Perspective view, select the head markers, beginning with the origin marker. For the head's origin marker, select the marker closest to the eyeball, then select the others.

    

13. In the Labeling Template Builder section, click Create again.
14. In the 3D Perspective view, check the axes and origin are shown for the new object.

    

15. Before proceeding, it is a good idea to save both subjects (Wand and Head). To do this, on the Subjects Resources pane, right-click on the node for each subject in turn and then click Save Subject.

Specify Dikablis Eye Tracker device properties

After you have created both the Wand and the Head in Nexus, specify their properties on the System Resources tab.

1. On the System resources tab, click on the Dikablis Eye Tracker node, and in the General section of the Properties pane, in the Head Segment field, enter Head.
2. In the Eye Offset section, enter the relevant values (that is, the distance between the origin marker and the eye).

   Tip
   To find the relevant eye offset values, if your Vicon system includes video cameras, you can use overlay video. If not, you can measure the distance from the origin marker.

3. In the Calibration Object field in the Calibration section, enter the name of the calibration object (Wand).

   

You have now set up the eye tracker properties.

Calibrate eye tracking in Vicon Nexus

After you have added eye tracking to Nexus, created Head and Wand objects, and set the eye tracking properties, you can complete the final steps.

To calibrate the eye tracker in Nexus:

1. On the System Resources pane, under the expanded Dikablis Eye Tracker node, click the Eye node to select it.
2. Display a Data Correction view, to show both a 3D Perspective and Graph view.

   

   You should see the x and y values for the selected eye.
3. In the capture volume, place the wand 2–2.5 meters from the subject and get the subject to look at the origin marker (the middle marker at the top of the T).
4. On the System Resources tab, click the Dikablis Eye Tracker node and in the Properties pane, go to the Calibration section and click Add.
5. Move the wand to another part of the volume and click Add again.
   In the Samples box, 2 is displayed.
6. Repeat the previous step.
   After you have collected three samples, an eye vector and an eyeball are displayed in the 3D Perspective view.

   

7. Collect more samples (aim for at least five samples in total) to refine your results.

   Tip
   When collecting samples, place the wand in the bottom left of volume and have the subject look at the origin marker. Pause for about a second and then in the Calibration section, and click Add. Then place the wand in the top left of the volume, and have the subject look at the origin marker. Again, pause, and click Add. Repeat with the wand at the top right of the volume, and then at the bottom right of the volume. Continue to move the wand and click Add until the eye gaze vector accurately tracks the origin marker.

8. When the eye tracker system has been calibrated (and if the subject is looking at the origin marker), in 3D Perspective view, the eye gaze vector will pass through (or point to) the origin marker of the calibration wand, depending on how far the subject's head is from the wand.

   

9. View the results in a 3D Perspective view.
10. To check that the eye tracks the wand correctly, record a short trial.