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Clarification of the Transverse Mercator projections allowed in INSPIRE


Question raised by Poland about the conformance to the Coordinate reference systems mandated in the INSPIRE Implementing Rules and associated Technical Guidelines, if the country stick to its national projected coordinate reference system (national CRS PUWG 1992 (EPSG:2180) when providing data for the Directive. This aspect is not totally clear when reading the corresponding text in the Implementing Rule.

In particular, the parameters of the Polish national system (longitude of origin, scale factor, etc.) are different than those defined for the ETRS89-TMzn (projected CRS allowed by INSPIRE.

It was also asked if it is really that important for the INSPIRE interoperability to provide raster data in ETRS89-TMzn instead of using other transverse Mercator projections, since re-projection of Elevation and Orthoimagery data sets implies a big burden for Member States (costs and time for transforming data, need for computer and storage resources, loss of data quality, etc.) whereas this kind of transformations may practically be obtained on-the fly for enclosed geographical areas using most GIS software tools.

Summary of discussion

The topic counted with the participation of an expert from the former INSPIRE Annex I Reference Systems Thematic Working Group (TWG-RS), which brought light to the question.

The text from the Implementing Rule on Interoperability of Spatial Data Sets and Services (IR ISDSS) is not specific enough in the corresponding section (1.3.2), i.e. when reading the requirement establishing the ETRS89 Transverse Mercator projected CRS for INSPIRE data provision someone may interpret that other Transverse Mercator projections (e.g. applied in Member States) are also valid for such purpose. This is mainly due to the fact that no EPSG codes were explicitly included in the statement, in contrast to the Technical Guidelines.

The intervention of the expert clarified that EPSG codes were intentionally omitted from the text of the Implementing Rule, because it is not an official coordinate reference system registry.

As a conclusion, a proposal for re-phrasing the corresponding section of the IR ISDSS is going to be proposed to the MIG-T.

Discussion thread (closed)

Proposal for MIG-T

The following minor rewording for section 1.3.2 of the IR ISDSS is proposed to the MIG-T to prevent further misunderstandings.

1.3.2.  Two-dimensional Coordinate Reference Systems

  • Two-dimensional geodetic coordinates (latitude and longitude) based on a datum specified in 1.2 and using the parameters of the GRS80 ellipsoid.
  • Plane coordinates using the ETRS89-LAEA coordinate reference system.
  • Plane coordinates using the ETRS89-LCC coordinate reference system.
  • Plane coordinates using the ETRS89-TMzn coordinate reference system.

Additionally, the Technical Guidelines document should be revised accordingly - especially if the IR rewording is postponed.

This proposal is forwarded to MIG-T for further analysis and potential endorsement.

Elevation, Ortho & Grids

Elevation, Ortho & Grids

INSPIRE Thematic Cluster Elevation, Orthoimagery, Reference systems, Geographical grids - Join this group to share your knowkledge, learn and collaborate in solving issues related to the Elevation, Orthoimagery, Reference systems and Geographical grids themes