Method and system for determining position and orientation of a measuring instrument

A system comprising a first measuring instrument, MI including a retroreflector unit;

• a second MI;
• and at least one target, TGT, said system being arranged for determining position and orientation of the first MI, wherein
• the at least one TGT includes at least one identification device configured to enable said TGT to be identified in an image capturing said TGT;
• the second MI comprising at least one second optical radiation source, configured to emit optical radiation when activated, and a position calculating circuit, comprising an angle measuring system and a distance measuring system (126), adapted to measure angle and distance to the first MI and the at least one TGT, respectively;
• the first MI further comprising:
• at least one first optical radiation source configured to emit optical radiation when activated and a control module adapted to selectively activate and deactivate the at least one first optical radiation source;
• a communication module adapted to, on instruction from the control module, communicate control signals to the second MI for activating or deactivating the at least one second optical radiation source, the communication module being further adapted to receive signals from the second MI indicating distances and angles determined by the second MI;
• and
• at least one imaging module adapted to, on instruction from the control module, capture an image, wherein the control module is adapted to cause the at least one imaging module to capture images including alternating activation and deactivation of the at least one second optical radiation source, and produce an image representation of each captured image;
• a processing module adapted to:
• create differential images using said image representations;
• extract information regarding objects being present in the differential images;
• distinguish the second MI and the at least one TGT, respectively, from any other objects present in the images using said extracted information;
• wherein the processing module is further adapted to, on a condition that the second MI and the at least one TGT can be distinguished from any other objects present in the images:
• on basis of said extracted information, process any of the image representations to determine angular information of the second MI and/or the at least one TGT with respect to at least one axis, respectively;
• and
• on basis of angle and distance to the second MI and the at least one TGT, respectively, and the angular information, estimate orientation of the first MI.