gf_interpolated_on_grid — interpolates a field defined on mesh_fem 'mf' on a cartesian grid [X(1),X(2),...] x [Y(1),Y(2),...] x ...
G=gf_interpolate_on_grid(mf,U,X,Y,...)
Interpolates a field defined on mesh_fem 'mf' on a cartesian grid [X(1),X(2),...] x [Y(1),Y(2),...] x ...