6.4.22.1 Coordinate reference systems

From Geostandards

The current version of the data specification is version 3.0. The document is available here.

This page currently contains the executive summary from the data specification document:

Coordinate reference systems are included in Annex I, which means that they are considered as reference data, i.e. data that constitute the spatial frame for linking and/or pointing to other information that belong to specific thematic fields as defined in the INSPIRE Annexes II and III.

The INSPIRE specification on Coordinate reference systems has been prepared following the participative principle of a consensus building process. The stakeholders, based on their registration as a Spatial Data Interest Community (SDIC) or a Legally Mandated Organisation (LMO) had the opportunity to bring forward user requirements and reference materials, propose experts for the specification development, and participate in the review of the data specifications. The Thematic Working Group responsible for the specification development was composed of geodetic and mapping experts coming from Portugal, Slovenia, France, Germany, Italy, Sweden, the UK and the Netherlands, all of them for many years involved in activities aiming to establish uniform geo-referencing within Europe. Due to the close links between and the special technical nature of the two themes of Coordinate reference systems and Geographical grid systems, the specifications of both themes were developed by one thematic working group.

Coordinate reference systems (hereafter: CRS) play a specific role that is quite different from the other themes in the Directive’s annexes. Contrary to the other themes the CRS specification does not concern a downloadable or viewable thematic data set. Rather, it presents a basic functionality allowing the harmonised and interoperable geographic localisation of spatial objects defined by the other INSPIRE thematic data specifications. Therefore, the methodology developed by the Drafting Team Data Specifications is only partly applicable to the work of this Thematic Working Group.

The specific task of the definition of the CRS therefore consists in taking the right decisions on the choice of one (or a limited number of) coordinate reference systems and map projections that will ensure a common basis for the geographical harmonisation between all the other themes defined in the Annexes of the Directive. There are however themes for which in addition to linear systems (that are usually used for the horizontal component) parametric, or on non-length-based systems are used for the vertical component.

There are also themes that may require temporal references. The referencing by parameters and temporal reference systems is not defined in general by the theme CRS. However, it is required that when data are exchanged using such reference systems, this is either specified using the ISO 19111-2 standard, or it is linked by reference to a document explaining the reference system.

There are specific parametric reference systems for the vertical component which are used by the atmospheric and oceanographic communities, and in the case of the atmospheric reference system, there is an existing ISO standard (ISO 2533:1975) which defines the International Standard Atmosphere.

In the free ocean depths, observations of temperature, salinity etc. have no direct height measure. Pressure is the parametric reference system used and any measure of depth is an approximation or inferred value based on the vertical profile.

In the free atmosphere, aircraft use barometric pressure, scaled as heights and appropriately calibrated to a surface datum to ensure separation. Relative height differences measured by pressure are not appreciably affected by changes in the actual surface pressure. Here too, there are no direct height measurements.

In 1951, the International Civil Aviation Organisation (ICAO) incorporated the International Standard Atmosphere (ISA) into international law under Annex 8 of the Convention on International Civil Aviation (the Chicago Convention, 1947). ISO adopted the Standard Atmosphere as ISO 2533:1975 in the range 2km to 32km. (Manual of the ICAO Standard Atmosphere: Doc 7488/3).

The document provides the result of the specification of the CRS. It contains elements that will be proposed as part of the draft Implementing Rule on interoperability of spatial data sets and services. These elements are clearly indicated in the document as “requirements”. The other parts of the documents give clarification, background information and examples and are intended as part of the technical guidance documents accompanying the Implementing Rule.

The cornerstone of the specification development was the definition of the Directive on Coordinate reference systems as being “Systems for uniquely referencing spatial information in space as a set of coordinates (X, Y, Z) and/or latitude and longitude and height, based on a geodetic horizontal and vertical datum”.

For the horizontal component, INSPIRE will mandate the use of the European Terrestrial Reference System 1989 (ETRS89) for the areas within the geographical scope of ETRS89. The International Terrestrial Reference System (ITRS) or other geodetic coordinate reference systems compliant with ITRS shall be used in areas that are outside the geographical scope of ETRS89. Compliant with the ITRS means that the system definition is based on the definition of the ITRS and there is a well established and described relationship between both systems, according to ISO 19111:2007 Geographic Information – Spatial referencing by coordinates.

For the height component on Land, INSPIRE will mandate the use of the European Vertical Reference System (EVRS) for the areas within the geographic scope of EVRS. Other vertical reference systems related to the Earth gravity field shall be used to express gravity-related heights in areas that are outside the geographical scope of EVRS.

INSPIRE will adopt barometric pressure and the ISA as the vertical reference system for the free atmosphere, and barometric pressure for the free ocean.

For depth values of the sea floor in marine areas with an appreciable tidal range, the Lowest Astronomical Tide is already mandated by Technical Resolution A2.5 of the International Hydrographic Organisation (IHO), and may be used as an exception in some themes. In marine areas without an appreciable tidal range, in open oceans and effectively in waters deeper than 200m tide is not measured since it has no significant impact on the accuracy of the sounding.

The requirements and recommendations Map projections are based on the results from the “Map Projections for Europe” workshop14. These are:

• Lambert Azimuthal Equal Area (ETRS89-LAEA) for pan-European spatial analysis and reporting, where true area representation is required;
• Lambert Conformal Conic (ETRS89-LCC) for conformal pan-European mapping at scales smaller than or equal to 1:500,000;
• Transverse Mercator (ETRS89-TMzn) for conformal pan-European mapping at scales larger than 1:500,000.

These projections shall be available in INSPIRE transformation services.

For regions outside of continental Europe, for example for overseas MS territories, the MS shall define a map projection they consider most suitable for the purpose. Moreover, different INSPIRE themes or applications may use appropriate map projections, for example if the data characteristics require large scale mapping. In these cases the map projections shall be well documented to allow the conversion to geographic coordinates and an identifier shall be created, according to ISO 19111.

For the rendering of spatial information for INSPIRE View Services, and in case there is a need for plane coordinates, the “Plate-Carrée” projection is recommended for the non-polar regions. For the polar regions a Polar stereographic projection is recommended.

This document contains also the identifiers for the different types of coordinates that shall be used.

← previous

Infrastructure for Spatial Information in the European Community (INSPIRE)

next →