Patent ID: 7696899

Claim:
A marker navigation device for determining or tracking a location of a marker device attachable to an object, said marker device including a plurality of markers having known dimensions and being in a known positional relationship relative to each other, comprising: a detection device operative to detect signals emitted by or reflected from the plurality of markers, wherein in first locations of the detection device relative to the marker device, detection of signals from one marker of the plurality of markers is restricted or impossible due to a location of another marker of the plurality of markers, and in second locations of the detection device relative to the marker device, the plurality of markers are detectable by the detection device; a processing device communicatively coupled to the detection device and configured to calculate the first relative locations based on the relative locations of individual markers of the plurality of markers and based on the known dimensions of the plurality of markers, and calculate an actual location of the marker device relative to the detection device based on detected signals from at least one marker of the plurality of markers, the known locations of the plurality of markers relative to each other, and the known dimensions of the plurality of markers, and determine whether the actual relative location of the marker device is one of the first locations; and a warning device communicatively coupled to the processing device and operative to output a warning signal when the actual relative location is one of the first relative locations.