In Tokamak devices the accuracy and the robustness of the control system rely on the precise and quick identification of plasma geometry. For this purpose, at JET a code is employed that computes the flux map in real time simply by interpolating the magnetic measurements. A simple plasma model has been developed to help the fitting procedure and to improve the boundary reconstruction while keeping the high computational speed. The plasma presence is taken into account by using a set of filamentary currents placed inside the vacuum vessel. The filament position remains fixed during the plasma evolution and the current moment method has been chosen to determine the amount of current flowing in the filaments. The moments describe features of the plasma current distribution, thus separating internal field sources from external ones. The filaments preserve the consistency with the physics and provide at the same time a linear formulation that can be expressed in matrix product form, which makes this solution particularly suitable for real time implementation. With reference to the JET Tokamak, a wide range of configurations has been tested, verifying the reliability of the methodology and the correctness of the filament model.