[2] How to measure geographic relief ?

The Litto3D® Project

The French cartographic services - “SHOM” for the sea and the “IGN” for the land - united their resources and their ability to measure, in high definition, the relief of the French costal zone, resulting in the Digital Terrain Model (DTM) dataset.

The three methods used

Topographic aerial laser (land)

Bathymetric aerial laser (sea)

Multi-bundles sounder (for underwater areas unaccessible by bathymetric laser)

Costal zones measured

For the sea, maximum limit of 10 meters in depth

White zones are areas without data

For the land, maximum limit of 2 kilometers inland

High definition : one meter resolution

Every square of 1×1 meter represents 3 values defining the geographic position : latitude, longitude and altitude. Combined, the squares form a network of data called a Digital Terrain Model (DTM).

SHOM : Service Hydraugraphique et Océanographique de la Marine

IGN : Institut Géographique National