  During the last years, the emerging field of Augmented and Virtual Reality
(AR-VR) has seen tremendous growth. An interface that has also become very
popular for the AR systems is the tangible interface or passive-haptic
interface. Specifically, an interface where users can manipulate digital
information with input devices that are physical objects. This work presents a
low cost Augmented Reality system with a tangible interface that offers
interaction between the real and the virtual world. The system estimates in
real-time the 3D position of a small colored ball (input device), it maps it to
the 3D virtual world and then uses it to control the AR application that runs
in a mobile device. Using the 3D position of our "input" device, it allows us
to implement more complicated interactivity compared to a 2D input device.
Finally, we present a simple, fast and robust algorithm that can estimate the
corners of a convex quadrangle. The proposed algorithm is suitable for the fast
registration of markers and significantly improves performance compared to the
state of the art.
