1. A polarimetric measurement method of a planar object carrying patterns repeated regularly and forming the lines of a grid including the generation of an excitation incident beam on said object forming a measuring beam whereof the orientation relative to the object is represented by an angle of incidence θ and an azimuthal angle φ, characterised in that a first measuring is carried out at zero order, under an angle of incidence θ 1 and for a first azimuthal angle φ 1 , a second measurement at least is carried out at zero order, under an angle of incidence θ 2 and for a second azimuthal angle φ 2 , the polarisation of the incident beam is modulated and the polarisation of the reflected beam is analysed for each measurement so as to obtain experimental polarimetric data, theoretical polarimetric data is calculated for a model object of the real object, said model object including parameters adjustable using a formalism of electromagnetism, the object is characterised by conducting an iterative comparison of the measurements with the theoretical polarimetric data for different values of the adjustable parameters.