Patent ID: 8125629

Claim:
A tracking method, in which a target point provided with a reflector is tracked by a measurement beam (M) of a laser tracker, comprising the steps of: in an ordinary tracking mode (A), data for controlling the direction of the measurement beam (M) is derived from the detection of the measurement beam being reflected by the reflector, and in an extraordinary tracking mode (B), the data for controlling the direction of the measurement beam (M) is derived from data being registered by an overview apparatus, wherein the overview apparatus has a known position and orientation relative to the measurement beam (M), wherein the extraordinary tracking mode (B) is active when no measurement beam reflected by the reflector is detected, wherein in the extraordinary tracking mode (B), the data for controlling the direction of the measurement beam (M) is computed from a direction to the target point being determined from data registered by the overview apparatus, and from the known position and orientation of the overview apparatus, wherein the overview apparatus is an overview camera, the data registered by the overview camera are image coordinates, and the target point is in addition identified by the overview camera, and wherein the target point is identified on images registered by the overview camera with the aid of a plurality of light points or reflected marking elements, which are arranged around the reflector and imaged by the overview camera.