  In order to analyze the geometric quality of any surface we have defined a
shape language that can be used in tolerancing and metrology softwares. Modal
parameters defines a shape langage allowing to describe geometric variations
associating undulation, form, position, orientation and dimensions. It defines
a geometric basis, easy to use by a simple user or deeply by an expert. The
principal properties of this basis are the exhaustiveness and the metric of the
parameters. We can use either natural mode shapes that can be modified by
technological mode shapes.
