Patent ID: 8860809

Claim:
A tracker unit for a measuring instrument including an instrument body, the tracker unit configured to distinguish at least one specific target comprising at least one retroreflector from other targets and other reflective objects in a vicinity of the measuring instrument, the tracker unit comprising: a plurality of photosensors, each of the plurality of photosensors configured to generate a signal corresponding to intensity of reflected optical radiation impinging on a corresponding one of the plurality of photosensors; a first optical radiation source and at least one second optical radiation source, each of the first optical radiation source and the at least one second optical radiation source being arranged in the instrument body and configured to emit optical radiation when activated, the first optical radiation source being coaxially arranged in relation to at least some of the plurality of photosensors and the at least one second optical radiation source being eccentrically arranged in relation to the first optical radiation source; a control module configured to, at least once, selectively activate and deactivate the first optical radiation source and the at least one second optical radiation source, and cause the plurality of photosensors to, generate at least one first set of signals during a first period when the first optical radiation source is activated and the at least one second optical radiation source is deactivated, and generate at least one second set of signals during a second period when the at least one second optical radiation source is activated and the first optical radiation source is deactivated; and a signal processing module configured to, extract first information regarding a presence of at least one reflective object in a vicinity of the measuring instrument based on the at least one first set of signals, extract second information regarding the presence of the at least one reflective object in the vicinity of the measuring instrument based on the at least one second set of signals, and compare the first extracted information and the second extracted information to distinguish the at least one specific target from the other targets and the other reflective objects in the vicinity of the measuring instrument.