Method for determining the path of a measurement beam of an interferometric measuring device, and measuring device for interferometric measurement of an object under measurement

A measurement apparatus for interferometric measurement of a measurement object, the measurement apparatus comprising:

• one or more beam sources configured to generate at least one measurement beam and at least one reference beam,
• a detector,
• an evaluation unit connected to the detector configured to evaluate measurement signals from the detector, an image recording unit,
• the measurement apparatus is configured to guide the measurement beam to at least one measurement point on the measurement object and to superimpose the measurement beam, which has been at least partially reflected or scattered by the measurement object, and the reference beam on a detection surface of the detector such that a superimposition or interference signal between measurement beam and reference beam is measurable by the detector,
• the evaluation unit (9) is configured to determine the beam path of the measurement beam, and is configured to:
• A. record a plurality of spatially resolved measurement object images of at least one measurement surface of the measurement object from different perspectives by the image recording unit;
• B. create a three-dimensional measurement object model which comprises at least the measurement surface of the measurement object by the plurality of spatially resolved images of the measurement surface;
• C. provide a measuring head model which comprises at least one measuring head element which is related to the measurement beam (6) in a specified way;
• D. create a mapping between coordinates in the three-dimensional measurement object model and coordinates in the measuring head model with the aid of a first structure in the measurement object model and a second structure in the measuring head model and based on a spatial relationship between the first and second structure;
• E. determine the measurement beam path by carrying out at least two of the following steps by the evaluation unit (9):
• Ei. determining coordinates of at least one location, which is located on an optical axis defined by the measurement beam (6) or which is spatially related thereto, based on the measuring head model;
• Eii. determining a direction vector specified by a measurement beam propagation direction (7) based on the measuring head model;
• Eiii. determining coordinates of a measurement beam point of incidence of the measurement beam on the measurement object based on at least one spatially resolved image which comprises at least one of the measurement beam point of incidence on the measurement object (8) or at least one auxiliary beam point of incidence of an auxiliary beam with a specified spatial relation to the measurement beam (6).