A method essentially comprising a step of storing each plot mesh. Each plot mesh receiving plots sent thereto by detector means and retaining in memory at least the altitude of the highest plot and the number of plots neighboring said highest plot in said mesh. The altitude and the number of plots neighboring are updated each time a new plot is sent to the plot mesh. A step of rejecting plot meshes is presenting a number of neighboring plots that is less than a predetermined rejection threshold value. The rejection threshold value is a function of the position of the mesh relative to the detector means. A step is preparing the local terrain elevation database from the plot meshes (M(i,j)) that are not rejected.