You can download a preprint of this article:
Spatial calibration of an optical see-through head mounted display
Gilson, S.J., Fitzgibbon, A.W. and Glennerster, A.
Journal of Neuroscience Methods, 173, 140-146 (2008)
We present here a method for calibrating an optical see-through Head Mounted
Display (HMD) using techniques usually applied to camera calibration
(photogrammetry). Using a camera placed inside the HMD to take pictures
simultaneously of a tracked object and features in the HMD display, we could
exploit established camera calibration techniques to recover both the intrinsic
and extrinsic properties of the~HMD (width, height, focal length, optic centre
and principal ray of the display). Our method gives low re-projection
errors and, unlike existing methods, involves no time-consuming and error-prone
human measurements, nor any prior estimates about the HMD geometry.
There is more information about the calibration method here.
Science direct link to article (if you have a subscription) of I can email (a.glennerster "at" reading.ac.uk) a copy on request.