A graphic data-acquisition system which employs an active tracking system provides a retrofittable apparatus for converting a substantially planar surface into an electronic data capture device, in which the components of the system are readily retrofittable, at relatively low cost, to a wide variety...http://www.google.com/patents/US6266051?utm_source=gb-gplus-sharePatent US6266051 - Retrofittable apparatus for converting a substantially planar surface into an electronic data capture device
