The New triangulation of France (NTF) sometimes wrongly called " system Lambert " (of the name of projection which is associated for him) geodetic Système is a covering the Territoire French subway. Today it leaves room to RGF93.

This Triangulation similar to those carried out by Cassini and the engineers geographers, pursues the goal of the realization of a national Cartographie.

Origin

It is about a two-dimensional realization carried out by angular measurements of the end of the XIXe century at 1991. The scaling is ensured by the integration of 15 bases of a precision of 10^-6D. the orientation results from the observations of 10 points of Laplace (precision of some 10^-6). The definition of matérialisation is of level centimetric (engraved cross of the granite terminals).

A hierarchy of cover of the Territoire associated with the possibilities of calculation brings a succession of levels of thickening: first order of chain (of which the first level is the Méridienne of France), first complementary order, second order, then third and fourth order. The whole of the observations is organized in a homogeneous way. On the other hand, calculations following one another in blocks of points progressively of the missions of ground, do not authorize the total coherence promised by the quality of the observations (some 10^-6).

The planimetric coordinates of a point in NTF are of the Cartesian type: Is, Northern (E; NR)

Matérialisation

The 70.000 geodetic sites (more than 80.000 if the points of 5th order or complementary triangulation is also counted) are regularly distributed on the national territory, and thus materialize system NTF with an average relative precision about 10^-6 (i.e. a few centimetres between two close points).

1. Principal network:

• 800 points of 1st order separated by approximately 30 km
• 5.000 points of 2nd order separated by approximately 10 km
• 60.000 points of 3rd and 4th order separated by approximately 3 km

2. Complementary network:

• 20.000 points of various precise details

IGN ensures the conservation of this networks and places at the disposal of the public the coordinates of each consultable point on a dedicated waiter.