Abstract: Aiming at the problem of model based definition (MBD) in the assessment of coherence
between product geometry definition and measurement, GPS (geometrical product specification and
verification) is proposed to be applied to model definition. The solution scheme is established based
on the duality principle of GPS, and key technologies of GPS used in model definition are analyzed.
GPS used in MBD is illustrated through face-gear model definition examples. Combined with the
example of the face-gear tooth surface accuracy assessment, the impact of product assessment is
expatiated. Thus, an idea is provided for the combinative application of MBD and GPS.

Key words: GPS technologies, model definition, application, example