Retroreflector acquisition in a coordinate measuring device

A three-dimensional (3D) measuring system comprising:

• a tracker including a source of light, a position detector, one or more target cameras, and a tracking system, the source of light operable to emit a beam of light along an optical axis of the tracker, the position detector operable to produce an electrical signal based at least in part on a position of light on a surface of the position detector, the position detector having a retrace point, the tracking system operable being to steer the optical axis;
• a processor coupled to the tracker, the processor operable to execute computer instructions that, when executed on the processor includes:
• determining whether the tracker is in a retro-follow mode;
• for the tracker in the retro-follow mode:
• determining whether the beam of light emitted on the optical axis of the tracker is detected by the position detector;
• when the beam of light is detected by the position detector, tracking on a retroreflector with the tracking system by moving the beam of light to arrive at the retrace point;
• and
• when the beam of light is not detected by the position detector, turning off the beam of light, identifying the retroreflector in first images of the one or more target cameras with the beam of light off, steering the optical axis toward the retroreflector with the beam of light off until a retroreflector acquisition criterion has been satisfied by the first images, and thereafter turning on the beam of light.