Reference Frames – Projects

NKG GNSS Analysis centre (NKG AC):

The goal of the NKG GNSS Analysis Centre (NKG AC) project is to produce a common, harmonized, densified and continuous ITRFyy solution for the Nordic area. Such solution is needed for various purposes, most notably for maintaining of the national reference frames (ETRS89) in the Nordic and Baltic countries as well as an accurate link to global reference frames. It is also essential data for modelling crustal motions, e.g. caused by Glacial Isostatic Adjustment (GIA). All Nordic and Baltic countries are actively participating as NKG local analysis centres (LAC) and sub-networks are combined to NKG daily and weekly solutions. Subsequently these solutions are stacked and analyzed to obtain coordinates, velocities and their uncertainties. More details in:

  • Lahtinen S., Häkli P., Jivall L., Kempe C., Kollo K., Kosenko K., Pihlak P., Prizginiene D., Tangen O., Weber M., Paršeliunas E., Baniulis R., and Galinauskas K. (2018): First results of the Nordic and Baltic GNSS Analysis Centre, Journal of Geodetic Science, 8:1 (2018), 34-42.
  • Lahtinen S., Jivall L., Häkli P., Kall T., Kollo K., Kosenko K., Galinauskas K., Prizginiene D., Tangen O., Weber M., Nordman M. (2019): ITRF2014 Densification for the Nordic and Baltic Countries. GPS Solutions (2019) 23:95,
  • Lahtinen S., Jivall L., Häkli P., Nordman M. (2022): Updated GNSS velocity solution in the Nordic and Baltic countries with a semi-automatic offset detection method. GPS Solutions 26, 9 (2022).

NKG transformations:

The goal of the NKG transformation project is to create and maintain an accurate link between global and national reference frames. Nordic and Baltic countries are affected by the Glacial Isostatic Adjustment (GIA) that is causing intraplate deformations up to a few millimeters per year in horizontal coordinates and up to a centimeter per year in heights. These motions need to be accounted for in order to reach sub-centimeter transformation accuracy from global reference frames to official national ETRS89 realizations. NKG has released land uplift models and transformation methodology and parameters that together enable accurate link to global reference frames. To make NKG transformation available to users, it has been implemented to PROJ. More details:

  • Häkli, P., M. Lidberg, L. Jivall, T. Nørbech, O. Tangen, M. Weber, P. Pihlak, I. Aleksejenko and E. Paršeliunas (2016): The NKG2008 GPS campaign – final transformation results and a new common Nordic reference frame. Journal of Geodetic Science. Volume 6, Issue 1, ISSN (Online) 2081-9943, DOI:, March 2016.
  • Häkli P., Lidberg M., Jivall L., Steffen H., Kierulf H.P., Ågren J., Vestøl O., Lahtinen S., Steffen R., and Tarasov L. (2019): New horizontal intraplate velocity model for Nordic and Baltic countries. In FIG Working Week 2019 Proceedings: Geospatial information for a smarter life and environmental resilience, Hanoi, Vietnam, 22 – 26 April 2019. (
  • Knudsen T., Evers K., Hjelle G.A., Valsson G., Lidberg M., Häkli P. (2019): The bricks and mortar for contemporary reimplementation of legacy Nordic transformations. Geophysica (2019), 54(1), 107–116. (
  • Häkli P., Evers K., Jivall L., Nilsson T., Himle S., Kollo K., Liepiņš I., Paršeliūnas E., Vestøl O., and Lidberg M. NKG2020 Transformation: An Updated Transformation between Dynamic and Static Reference Frames in the Nordic and Baltic Countries. Journal of Geodetic Science 13, no. 1 (June 14, 2023): 20220155.