# SK-42 reference system

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Soviet geodetic datum

The **SK-42 reference system** is a [geodetic datum](/source/Geodetic_datum) established in the [Soviet Union](/source/Soviet_Union) in 1942 as *Systema koordinat* ([Russian](/source/Russian_language): Система координат 1942 года). It was used in geodetic calculations, notably in military mapping and determining state borders.

SK-42 is based on the **Krasovsky 1940 ellipsoid**, a locally best fitting [reference ellipsoid](/source/Reference_ellipsoid) named after [Feodosy Krasovsky](/source/Feodosy_Krasovsky). It has a [semi-major axis](/source/Semi-major_axis) (equatorial radius) *a* of 6,378,245 m, and an inverse flattening 1/*f* of 298.3 [1][2]: 220

SK-42 served as a foundation for developing the [SK-63 reference system](https://en.wikipedia.org/w/index.php?title=SK-63_reference_system&action=edit&redlink=1) which was created and used primarily for civilian and industrial development purposes.[1] It was later linked to the [geocentric coordinate system](/source/Geocentric_coordinate_system) [PZ-90](/source/PZ-90) via a [datum transformation](/source/Datum_transformation).[1]

## Citations and notes

1. ^ [***a***](#cite_ref-mazurova_1-0) [***b***](#cite_ref-mazurova_1-1) [***c***](#cite_ref-mazurova_1-2) E.M. Mazurova; S.M. Kopeikin; A.P. Karpik (2017). "Development of a terrestrial reference frame in the Russian Federation". *Studia Geophysica et Geodaetica*. **61** (4): 616–638. [Bibcode](/source/Bibcode_(identifier)):[2017StGG...61..616M](https://ui.adsabs.harvard.edu/abs/2017StGG...61..616M). [doi](/source/Doi_(identifier)):[10.1007/s11200-015-1106-4](https://doi.org/10.1007%2Fs11200-015-1106-4). [S2CID](/source/S2CID_(identifier)) [133884317](https://api.semanticscholar.org/CorpusID:133884317).

1. **[^](#cite_ref-2)** Office, United States Naval Observatory Nautical Almanac; Office, Great Britain Nautical Almanac (2005). [*Explanatory Supplement to the Astronomical Almanac*](https://books.google.com/books?id=uJ4JhGJANb4C). University Science Books. [ISBN](/source/ISBN_(identifier)) [9781891389450](https://en.wikipedia.org/wiki/Special:BookSources/9781891389450).

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