ARToolKit is a computer vision tracking library that allows for the creation of augmented reality applications that overlay virtual imagery on the real world. To do this, it uses video tracking capabilities in order to calculate the real camera position and orientation relative to square physical markers in real time. Once the real camera position is known a virtual camera can be positioned at the same point and 3D computer graphics models drawn exactly overlaid on the real marker. So ARToolKit solves two of the key problems in Augmented Reality; viewpoint tracking and virtual object interaction.