Coordinate System Reforms
Modern coordinate systems utilised in Rauma
On 19 November 2012, the city of Rauma started to use European standard ETRS-GK22 horizontal coordinate system and N2000 vertical datum for all map and spatial data production.
The transition to new systems has improved national and regional exchange of information. Sharing of spatial data sets will be significantly improved. Satellite positioning devices also operate directly in the EUREF-FIN system, which facilitates survey work and system maintenance.
The change was based on the recommendations of public administration 163, 196 and 197 for the information management of municipal administration.
The system conversion was based on comprehensive, municipality wide GPS measurements which were used to determine transformation parameters between the old (KKJ) and the new coordinate system (EUREF-FIN).
Adopting N2000 vertical datum
Rauma has previously used N60 vertical datum. In addition, heights for some data sets are still in old NN vertical datum.
Vertical conversion can be based on so-called constant shift, which is a constant height correction between N60 and N2000 vertical datum. In Rauma, the constant correction is +0.337 metres. When transforming from NN to N2000, the constant correction is +0.614 metres.
Formulas for converting N60 and NN heights to N2000 heights:
H (N2000) = H (N60) + 0.337 m
H (N2000) = H (NN) + 0.614 m
Be careful to do the correction into the right direction!
Constant shift can be used to convert all elevation values of spatial data sets from N60 to N2000, except points with the highest accuracy, such as vertical control points. These points have their own method.
The theoretical mean sea level (MSL) is calculated from the mean sea level table according to the desired year and height system. The height of the N2000 vertical datum relative to the mean sea level is about 13 centimetres higher in Rauma (in 2017). Additional information on the mean sea level can be found from the website of Finnish Meteorological Institute.
Adopting N2000 vertical datum calls for special attention by planners and constructors
There are plenty of end users for vertical data, and their every day practices may vary a lot. It is important to have uniform methods for handling vertical information.
A general recommendation is that projects started in the old coordinate systems are completed in the same system. It is also possible to convert the coordinate data of an already started project into a new system if, for example, the project is only in its initial stage. In this situation too, it must be ensured that all parties are promptly informed about the changes to the plan. Especially during the transition period, it must be ensured which heights are used.