4. Control interfaces

We can define a 3D mouse (figure 7 ) by an interface that only allows the user to control three perpendicular translations and three perpendicular rotations in space. As already mentioned, a sensor can do the same, but a 3D mouse cannot measure the absolute location of the hand. The advantage of 3D mice is that they are technically easier to realize using voluntary hand movements. The consequence is generally a relatively low purchase price compared with location sensors.

Remember that, while it's not too difficult to "translate" any virtual object (cursor, part, etc.) in any direction using the three translation commands, cursor orientation is tricky. Rotations along three perpendicular axes are not commutative geometrical operations....