Position sensing and augmented reality

One of the greatest challenges for the emerging discipline of Augmented Reality (AR) is solving the visual registration problem i.e. aligning virtual computer graphics accurately over the real world scene to provide the user with a usefully “augmented” interactive experience. To achieve this goal the position and orientation of the user’s head must be measured with high accuracy and low latency. There is no general purpose technology that works outdoors or indoors (with unlimited range) to accomplish this. Addressing the application of reconstructing ancient Roman buildings in situ which once existed at a now green field archæological park in Colchester, an AR system has been developed. This consists of an optical look-through stereoscopic VR headset and a wearable computer, with GPS and computer vision being used for position determination. The Visual Positioning System (VPS) finds and identifies specially designed targets within the scene to work out camera location. The targets have unique signatures when the image is turned into a Region Adjacency Graph (RAG) resulting in robustness and reliability (no false positives). The GPS system uses two receivers: one on the archæological tourist and one at a base station in order to perform differential processing for greater positional accuracy. Initial evaluations were made of the ADXL202 “accelerometer on a chip” and of the LAMBDA method for high accuracy GPS positioning, with a view towards a multi-component hybrid solution for the registration problem. Currently, the VPS can work unassisted indoors or automatically initialise the registration for use of the lower accuracy GPS outdoors. The systems developed are inexpensive: the VPS uses laser-printed targets and a commodity PC for the visual processing, while the GPS is based on two inexpensive Garmin G12 receivers. The software developed in-house has been put into the public domain.