Motion study for remotely sensed data is a wide research field, involving tracking of structures, measurement of evolution and forecast. Several difficulties arise when tracking a vortex within oceanographic images: the structure is complex, and its evolution involves large changes of shape and topology. Therefore, the classical approach of motion based on the `small deformations' hypothesis does not hold: one must add exogeneous information, concerning the underlying physical phenomenon for instance. This information may be unavailable, or so complicated that a numerical treatment can not be carried out. We propose a surface based model that performs a global matching without relying on local features. It is defined by geometrical constraints that are a simplified approximation of the evolution model of the structure. This model is also applied to track a vortex within oceanographic images.