Frame of reference géoréférencées

Introduction

To indicate a place on the Earth using coordinates, it is necessary to associate a to them Frame of reference géoréférencées. There are several for historical, technical reasons and of use.

Until recently the technical systems of positioning were founded on the local principles (like the Triangulation) and thus in each area a specific frame of reference was defined. The possibility of defining total systems for the whole of the Earth appeared with the satellites in particular with the implementation of the Système GPS. As it to change frame of reference because should in particular be remade all the charts are rather complicated, old frames of reference are still frequently used.

A world frame of reference is inevitably vague because of the continental drift which induces displacements about a few centimetres per annum. Thus in a world system the punctual coordinates considered as fixed evolve/move what is not very practical.

It is often more practical to rather use plane coordinates in a cartographic system of Projection than of the geographical coordinates and as any system of projection deforms either the angles or the forms, it is useful to be able to choose the best system of projection according to its needs.

Classification of the frames of reference géoréférencés

One distinguishes several types of frames of reference géoréférencées:
  • geographical frame of reference. The coordinates are two angles called Latitude and Longitude generally expressed in degrees. The height with the top of the ellipsoid can be associated like third coordinate.
  • geocentric frame of reference. It is a Cartesian Frame of reference in space based on the center of the Earth and a first axis in the plan of the equator and intersecting the meridian line of Greenwich, a second axis in the same plan of the equator and orthogonal to the first and a third axis corresponding to the axis of rotation of the Earth. This type of system is especially used as intermediate system for calculations of change of system.
  • system of definition of Altitude. Altitude is measured as a distance along the vertical compared to a reference which is generally the sea level.
  • frame of reference projected. There exist many systems of cartographic Projection which make it possible to define coordinates on a plan.
  • the composition of a horizontal system and a definite vertical system a frame of reference.

Codes EPSG

The EPSG - European Petroleum Survey Group -, a group which disappeared now, defined a list of the frames of reference géoéréférencées and their associated codes to identify them. This list is available below on the site indicated in the bonds. These codes are in particular used in the standards of the Open Geospatial Consortium.

The whole of the elements interesting the national territory (historical systems & TOM included) are on line on the site of the IGN: Register of the geodetic internal frames of reference (RIG).

Geographical frames of reference frequently used

in Metropolitan France

in overseas French

Frames of reference projected frequently used

in Metropolitan France

In the overseas departments

In a general way, the use of a square UTM based on WGS84 implies a precision equalizes with that of the WGS84 (between 5m and 10m even less). For the DOM, the UTM is based on geodetic systems more precise (RRAF91, RGR92…) : the enforcement zone is thus reduced to that of the subjacent system and the precision is that of subjacent system.

See too

other articles

external bonds

  • ''' Site of the OGP Surveying and Positioning Committee in connection with codes EPSG '''
  • ''' Site of PROJ.4 - Cartographic Projections Library diffuses codes EPSG with the ASCII format '''
  • ''' Frames of reference for the overseas departments (IGN) '''
  • ''' Frames of reference for the communities of overseas (IGN) '''

Random links:Albinen | Cross from Oceania of football | Giovanni Battista Sammartini | Antoine Deparcieux (1753-1799) | Mauritius Telecom | J'arrive