This video shows how to track 3d head pose based on fiducial markers in the environment. 1 – Preparation Print out the fiducial markers (Apriltag). All markers need be printed with the same size. Place markers in the space where you want to track the head pose. Wear your Pupil Labs eye tracking headset and make a recording. Move slowly around the space. Tip: Try to record 2 to 8 markers every moment. 2 – Building a 3d model of the space Open Pupil Player Select the “Offline Head Pose Tracker” plugin. Click “Start detection” to detect markers in the recording. You can see the marker detection progress in the timeline. After marker detection is done, the 3d model will be built automatically. Click “Visualization 3d Window” “Open” to see the 3d model. The 3d model is being built… You can see the progress in the “Status” field 3 – Head pose Tracking After the 3d model done building, the camera poses will be calculated automatically. You can see the camera frustum moving in the Visualization 3d window. You can switch on “Show camera trace” to see the camera path through the space. You can export the 3d model and estimated head poses as csv files. See our documentation for more information on the export data format.