Automatic Marker Field Calibration

In many augmented reality applications a marker field (set of markers) is used to define the 3Dcoordinate transformation between the camera and the virtual objects. In most systems, the physical positions and pose of each marker relative to each others need to be measured in advance. This calibration process is often time consuming and inaccurate if done by hand. We present an automatic calibration process for a set of markers creating a marker field. Our automatic calibration can be used without any preparations and the markers may be placed in any 3D arrangement including even arbitrary angles and slanting planes. The calibration is a real time process and it does not need separate calibration phase. The user may lay markers randomly on suitable places and start tracking immediately. The accuracy of the system improves on the run as the transformation matrices are updated dynamically. The calibration can also be done as a separate calibration stage, and the results can be saved and used later with another application. In our implementation we used ARToolKit and its marker field implementation. However, the algorithms to create a marker field can be applied to create any type of feature/marker field mapping, not only ARToolKit compatible.