The Standard ISO 19111, Geographic information – Spatial referencing by coordinates defines
the conceptual scheme for describing the spatial referencing by coordinates.
This describes the data required to define the coordinates reference systems of
one, two and three dimensions as well as the information required to convert
the coordinates of one system to another.
In accordance with this Standard, a
coordinates reference system is made up of a coordinates system and a datum. As
regards the different datum types specified by the Standard, Geodetic Datums and Vertical Datums are those which are going to be used in this
module. The former require the description of an Ellipsoid and the latter don't.
In view of this classification, two
coordinates reference system groups have been created: Geodetic CRS and Vertical
CRS.
The Geodetic CRS are divided, in turn, into various types. Based on the
classification of the Standard ISO 19111
and in the classification which makes the EPSG
(European Petroleum Survey Group, www.epsg.org, currently OGP, International Association of Oil & Gas Producers) on its data
base, the following will be distinguished between: Geographic CRS, Geocentric CRS and Projected CRS.
Hence, the 4 coordinates reference system
groups which are going to be dealt with are:
Geographic
CRS
Geocentric
CRS
Projected
CRS
Vertical
CRS
To carry out the transformation of
coordinates between two different systems it is necessary to know the
transformation parameters of both systems into a common system which is WGS-84.
In view of the fact that two datum types are distinguished, geodetic and
vertical, geodetic datum transformations and vertical datum transformations
will be looked at in the following sections.
All the information, except that of
the user, which the application handles about coordinates reference systems,
datums, data transformations etc of the different countries around the world
derive from the EPSG data base in
its version 8.3 dated November 23th 2013.
Coordinates conversions and
transformations are carried out with the cartographic projections library PROJ.4 v. 4.8.0 (trac.osgeo.org/proj) dated March 6th 2012.
The management of the different
elements going to make up the geodesy module is carried out by means of the
options shown by the window below:
