====== HOWTO ======
Headtracking is a system allowing to cpature head position and movements, and convert them in data suitable in programs.

Sensor type , markers and tracking method alter the number of degrees of freedom,  with a maximum of 6 degrees of freedom :
  * X rotation (left-right rotation)
  * Y rotation (up-down rotation)
  * Z rotation (left-right lean)
  * X translation (left-right translation)
  * Y translation (up-down translation)
  * Z translation (front-back translation (zoom))

The most usual modes are :
  * 2DOF : X and Y rotation
  * 3DOF : X,Y,Z rotation OR X,Y rotation and Z translation (zoom)
  * 4DOF : X,Y rotation and X,Y translation
  * 5DOF : X,Y rotation and X,Y,Z translation
  * 6DOF : all axis

====== TRACKING METHODS ======
===== Gyroscopic Tracking =====
This tracking is acheived by detecting movements with gyroscopic devices or accelerometers, in each axis.

PROS :

  * Can track the full head movement (Very interesting if used with 3D VR goggles, full head movement can be used on a 1 per 1 basis).

CONS :

  * Electronic schematics more complex than an optical headtracker.
  * Needs a pos 0 calibration.
  * Based on the fact this kind of device only tracks movements (not positions), a progressive drift is unavoidable. Thus , it is often necessary to recalibrate the position 0.

===== Optical Tracking =====

==== Face recognition Tracking ====

This optical tracking uses an optical sensor to scan the user's face, and find some outstanding points, used as reference markers.

Head movements are decteted by the movements of those reference markers.


PROS :
  * low hardware cost

CONS :
  * Needs a pos 0 calibration
  * Usually needs a face recognition calibration, for each user.
  * Complex software.



==== Markers Tracking ====

This optical tracking uses an optical sensor to detect a set of markers, fastened to the head.
The optical sensor is setup to work in a high-contrast mode, to help dissociate markers from ambient light.

Head movements induce movements and twisting of the markers geometrical model image.

PROS :
  * Low cost
  * Low hardware needs
  * Since detection is made by analysing a simple geometrical model, the software is small and fast enough to work in realtime on most today's  personnal computers.

CONS :
  * Can't reproduce the full head movement capabilities (optical sensor looses sight on markers, past max angle)
  * Needs a pos0 calibration







====== EXISTING PRODUCTS ======

^  Poduct  ^  Commercial/Free  ^  Method  ^  Max.Capability  ^  Status  ^  WWW  ^
| TrackIR  | Commercial  | Optical / markers  |  6DOF  | Active  | http://www.trackir.com  |
| SPICA Helmet Tracker  | Commercial  | Optical / markers  |  6DOF  | Active  | http://www.spicatek.com/HeadTracker/Headtracker.htm  |
| 3D Visor  | Commercial  | Gyroscopic  |  6DOF  | Active  | http://www.3dvisor.com  |
| FreeTrack  | Free  | Optical / markers  |  6DOF  | Active  | http://www.free-track.org  |
| Cam2pan  | Commercial  | Optical / markers  |  2DOF  | ?  | http://www.mousevision.com/game/index.html  |
| Freelook  | Free  | Optical / markers  |  2DOF  | ?  | http://freelook.org/  |