1. A method for calibrating a three-dimensional imaging system the method comprising: providing first and second measurement units, the first measurement unit configured to acquire information from which locations of object features within a first measurement field can be determined in a first local coordinate system, the second measurement unit configured to acquire information from which locations of object features within a second measurement field can be determined in a second local coordinate system; determining first locations in the first local coordinate system of a first plurality of calibration features located in the first measurement field, and, based on the first locations, determining locations in the first local coordinate system of a second plurality of calibration features located in the second measurement field; determining locations of the second plurality of features in the second local coordinate system; and, deriving a transformation between the local coordinate systems and a common coordinate system based upon the locations of the second plurality of calibration features in the first and second local coordinate systems.