A relative keyboard, or predictive keyboard is a textual input method whereby 'keystrokes' are detected via machine vision, as movements relative to one another, instead of a discrete, unambiguous sequence of key-presses activating electrical circuits.

If the user is a touch-typist, never needing to look at the keys, this means they can type on any haptic-enabled surface, without requiring visual keys, or indeed any form of key at all.

Evolving out of projection keyboard systems first developed in 2005, a relative keyboard goes one step further, and removes the projection system.

The projection keyboard "virtual keyboard" used an infra-red scan based on optical recognition to detect objects such as fingers, passing through the space where the keys would be if they were physical. A relative keyboard can still do this, even without points of reference: it comes down to marking an arbitrary 'start' co-ordinate on the haptic surface.

Disadvantages are of course a lack of any auditory clicking sounds when a 'key' is pressed, however, they may find a market when combined with a solely VR based screen projection of a keyboard or input device - see an input panel in the VR, and the relative keyboard could sync with ease, regardless of the input type. Wall displays, keyboards, even piano keys, treated exactly the same way.

Links:

VR Interfaces: Virtual Keyboard

VR Interfaces: Relative Keyboard Prototype