1. A method of obtaining a local terrain elevation database from detector means on board a vehicle, said means sending measurement signals towards the terrain for which the database is to be determined and recovering at least some of said signals in the form of range images made up of a plurality of individual plots expressed in the form of three-dimensional coordinates, said method comprising, for the purpose of correcting false echoes by filtering them out: a step of subdividing said terrain in a horizontal plane grid using two-dimensional terrain meshes in a local geographical frame of reference; the horizontal grid-making step using at least two arrays of plot meshes that are mutually geographically offset such that two offset plot meshes share a portion in common and each has a respective distinct portion; wherein a neighboring plot is a plot in the same plot mesh as the highest altitude plot and the absolute value of the difference between its altitude and the altitude of said highest altitude plot is less than a predetermined value: a step of storing each terrain mesh in a plot mesh with a specific sub-step for each of the arrays, each stored plot mesh receiving from the detector means the plots it has sent and retaining in memory at least the altitude of the highest plot and the number of plots neighboring said highest plot in said plot mesh, said altitude and said number being updated for each plot newly sent into the plot mesh; a step of rejecting plot meshes that present a number of neighboring plots that is less than a predetermined rejection threshold value; and a step of preparing the local terrain elevation database from the non-rejected plot meshes; in which step false echoes contained in the plot memory are filtered out; the plot mesh retained for preparing the terrain elevation database being that one of the non-rejected plot meshes amongst the arrays that presents the greatest respective maximum altitude; and a digital terrain model is developed from the remaining plots.