# Coordinate Systems

In general we have to differ between geographic systems or projections.
In geographic systems the point on a position on the reference ellipsoid ( earth )
is given with Latitude and Longitude (these order is the usual form). Rarely seen is the cartesian form of the coordinates with three values in the three axis ( X,Y,Z ).
The ellipsoid were adapted for the different areas, this mounting with a defined center, twisting and scaling is named Datum. The prime meridian is the meridian where the longitude value is set to 0. Often the local systems uses a prime meridian through the capital city's. (NGO-1948/Oslo, ROMA40/Rom, NTF/Paris ) contrary to the prime meridian Greenwich. Sometimes both are still in use.

A projection is a mathematical conversion from the ellipsoid on a cylinder or cone ( then unrolled ) or directly to a plane producing a coordinate value pair with x/y, also designated to Easting/Northing. Im some systems (UTM) x/y is like the mathematic notation, others uses y for the Easting and x for Northing (e.g. Gauss/Krüger). So Easting/Northing is on the save side :-)
But there are also coordinate systems, in which the values increases to west instead of east and southing instead of northing ( like the Krovak-projection in Czechia ). So this is a little complicated ;-)

Worldwide in use is the geographic system WGS84. The GPS navigation satellites deliver their coordinates in this system. So the calculated coordinates from a GPS-receiver system is WGS84.
The related projection is UTM ( Universal Transverse Mercator ). This are 6°-Zones, who cover the whole earth. The 60 Zones are numbered( 01 = 177° West ) and completed with a character for north or south of the equator (e.g. UTM33N). UTM is valid for Latitude 80° south to 84° north.

The official reference system in Europe is ETRS89 ( European Terrestrial Reference System from 1989 ) and is fixed in the continent. Between WGS84 and ETRS89 are differences, because of the continental drift ( and a slight diff. in the reference ellipsoids WGS84 ? GRS80 ). This difference increases every year, but is still so small, that for normal use both systems are in fact ident. Only for use with RTK for geodesy survey this is of course important.

And all adopted (new) national coordinate systems are based on this ETRS89.

Austria

In Austria the official geographic system is the MGI. It is based on an Bessel ellipsoid and also named Datum Austria.
M34, M31 and M28 are the three corresponding projections from east to west.
Here is M34 the name for meridianzone 34 , - that means 34° easting of Ferro (today El-Hierro - Canary Islands) is the center merdian of that Gauss-Krüger projection. From Greenwich this meridian has a Longitude 16°20' (in MGI).
In Geotrafo x-values (Northing) with or without the -5-Mio. false northing are accepted. The common use of the coordinates is without the -5 Mio. So this is what the result shows. To avoid negativ y-values the Bundemeldenetz uses a false easting for the three zones ( BMN28, BMN31, BMN34 ).
Lamb-AUT stand for the Lambert Conformal Conic projection with standard paralells by 46° and 49° and the Origin Latitude with 47,5° (EPSG: 31287).

In future UTM will replace the Gauss/Krüger system.

Germany

In the old parts of Germany DHDN (Deutsches Hauptdreiecksnetz) is in use. It is based on the Bessel ellipsoid .
The projections are devided to 4(5) zones ( Gauss-Krüger ).
To the easting value ( y ) a constant of 500000 is added and mainly the zonenumber is preplaced.
geotrafo accepts the y-values with or without this zone number.

In the newer countries various systems were used.
So we can find the system S42/83, based on the Krassovsky ellipsoid (1940),
in use in (Mecklenburg-Vorpommern and) Sachsen-Anhalt.
Analogous to DHDN there are Gauß-Krüger zones ( Number 3 - 5 ) with the same properties. In Sachsen exist the system RD/83 ( Rauhenberg ), in Thüringen PD/83 ( Potsdam ).

Partially the switch to the ETRS89/UTM is already happened or is in process.

Switzerland

In Switzerland one system cover the whole country, the CH1903 with anchor point Bern/Sternwarte. It is based on a Bessel ellipsoid and also named Swiss Datum.

The projection is an oblique Mercator (LV03).
By addition of 600 or 200 km in y (Easting) and x (Northing) result in the so called Militärkoordinaten (LV-03M). The Zivilkoordinaten (LV-03C) without this constants are still in use in Liechtenstein.

The new CH1903+ (LV95) is corresponding to the CHTRF95, best fitting to CH1903. His projection LV95 differs from the old one up to 1.6 meter. To avoid confusion, an offset for the coordinates (y,x) is used - 2600 and 1200 km.

In geotrafo the calculation for the three swiss projektions are the same, they only differ through the offset values. So the deviation will be max. 1.6 meters.

Czechia/Slovakia

The system Krovak is the official projection in Czechia and Slovakia. This is an oblique conformal conic projection from the S-JTSK. In Geotrafo the Lamb Longitude-(Lambda-) value is related to Greenwich. ( Ferro - Greenwich => 17°40' ) [S-JTSK Ferro will be added in the next update]
Please pay attention to the fact, that the y-axis increses to west and the x-axis to south direction.

Luxembourg

The LURES (Luxembourg Reference System) is the national Datum with the ellipsoid Hayford or International 1924. The fundamental point is Laplace point in Belgium. A transverse Mercator projection (LUREF-TM) with the Origin in 49°50' Lat. and 6°10' Long. has a false Easting of 80 km and a false Northing of 100 km.

Netherlands

The Datum in Netherland is the named RD (Rijksdriehoeks) with the anchor point in Amersfoort and a ellipsoid Bessel 1841. In Geotrafo the Datum is named Amersfoort and the projection is called Rijksdriehoeks. I hope this will not cause a confusion. The older RD projection (EPSG 28991) don't have a shift value, but otherwise the same options. It is a oblique stereographic projection with a scale factor of 0.9999079 and the central point in Amersfoort.

Belgium

A Lambert cone projection with two standard paralells give the plane coordinates in Belgium (LAMB72) . The Origin is at 90° North and the central Meridian is 4°22'02,952" East. Based is the cone on a Hayford ellipsoid with an anchor point in Brüssel. This Datum is named BD72. For the european ETRS89 is also a Lambert cone projection defined, which is called Belgian Lambert 2008 ( in Geotrafo: LB2008 ). It replaces the former "Belgian Lambert 2005".

France

The older Datum is NTF (Nouvelle triangulation de la France) based on Clarke 1880 IGN's ellipsoid with the anchor point in Paris (Pantheon). Still in use are the Lambert cone projections named NTF I up to NTF IV . In the Carto variants the zone number *10E6 is added to the false northing. Originally this projections are with one standard paralell and a scale factor, but in Geotrafo a equivalent calculation with two standard parallels without the scale is in use. The new realization of the Datum is the RGF93 (Réseau géodésique français) with the GRS80 ellipsoid, - de facto ident with ETRS89. Similar to NTF exist 9 cone projections named CC 42 - CC 50, the numbers stand for the latitude origins. All have a constant false easting of 1700000. Please pay attention, that the geographic NTF coordinates have gon instead of degree, so 45°30' = 50gon 50gonminutes.

Spain

In Spain ED50 (European Datum 1950) is in use. The ellipsoid is Hayford(International 1924) and the anchor point is Potsdam - Helmert tower. For Spain there are various adopted transformation paramater sets. So the ES-ED50 is for the mainland without the area in the northwest (ZNW-ED50). For the Balearic islands BAL-ED50 is optimized. The projection of this Datums is a Transversale Mercator with UTM specific parameters ( scale, false eating ). The same way the coordinate system in Gibraltar is defined, for this small area with the Datum GIBR-ED50.

Portugal

Both Datums D73 with anchor point in Melrica and DLX with anchor point in Lisboa have the same Hayford ellipsoid and the same Origin with Lat. 39°40' and Long. 8°07'54.862" West. For each exist a Gauss-Krüger projection and a Military variant with false eastings and northing to avoid negative values. Further exist a system on a bessel ellipse (DLB) and a Bonne projection. The axis of this coordinatesystem shows against normal usage to south and west. The new realization is named PT06 with GRS80 and is equivalent to ETRS89. PT06-TM is the Transverse Mercator projection for it and again a military variant with the same false values like by the old systems. Only the central point of projection differs slightly. Therefore the results of old and new systems ar near together.

Ireland

In Ireland the older Datum Ireland 1965 uses the so called Airy Modified ellipse and the plane coordinates result from a Transverse Mercator projection with the central point at 53°30' N and 8° West, false northing and false eastings and a scale factor at central meridian of 1.000035. The plane area is subdivided in 25 square grids (A-Z) and an other notation of the coordinates is possilble (e.g. N 25317 42145 -> E 225317, N 242145 meter ). The Irish Transverse Mercator (ITM) is the new projection of the GRS80 ellipsoid for Ireland Area, has the same Origin like the Irish Grid but other false eastings and northings, - so there is not a confusion with it.

Great Britain

OSGB36 is the Datum for Great Britain, it uses the Airy 1930 ellipsoid and the prime meridian in Greenwich. The projection is a Transverse Mercator and also named National grid. The plane area is divided in square grid with 100x100 km and named with two letters and an other notation of the coordinates is possilble.

Norway

The NGO1948 uses a modified Bessel ellipsoid and the anchor point in Oslo (Observatory), which is also the prime Meridian for the geographic system. A Gauss Krüger projection in eight zones with various central meridians produces the plane coordinates. As new coordinate systems ETRS89 and UTM are adopted since 1997.

Sweden

The coordinate system that previously was used in Sweden is RT 90. In conjunction with the Transverse Mercator projection six zones exist. One, the "RT 90 2.5 gon V 0:-15" - Rikets nät - is valid for the whole country. In this naming "2.5gon V" means 2.5 gon (2°15') west of Stockholm is the central meridian. "0:-15" means false easting = 1500000 and false northing = 0. In all there are six projections from 7.5 gon west to 5 gon east. The new SWEREF99 is the realization of ETRS for Sweden. One Transversal Mercator projection with a scale of 0.9996 and 12 projections from 12° to 23°15 are defined. The SWEREF99-TM has a false easting of 500000 and all the others have 150000 meter and are for the southern or the northern part of the land.

Finland

In Finland the KKJ is the coordinate frame ( kartastokoordinaattijärjestelmä ) and the projection is a Gauss Krüger with a central meridian at 27° east of Greenwich and a false easting of 3500000 meter. This general projection is also named KKJ Uniform. But at all Finland is divided into 6 zones ( zone 0 - zone 5 ) with central merdians at equal distances of 3° Longitude. The false easting is in general 500000 meter plus the zone number * 10E6 . The new ETRS-TM35FIN is a UTM-similar projection with the central meridian at 27° east of Greenwich and a width of zone greater than 6°. With a distance of 1 degree the zones ETRS-GK19 to ETRS-GK31 are Gauss Krüger projections with scale 1 and false eastings of 500000 meter.

Denmark

An UTM projection on the ED50 with the ellipsoid Hayford / International 1924 is used in Denmark. For the core-land the zone 32 (central meridian at 9° east) is defined with a width more than 6°, Zone 33 is in use for island Bornholm. For the ETRS89/GRS80 realization are four Transverse Mercator projections dktm1H_h_DVR90 and dktm2H_h_DVR90 are for the mainland east or west of 10° Long., the dktm3H_h_DVR90 is for use in Sealand and dktm1H_h_DVR90 for Bornholm. All but one are with a scale of 0.99998 and all with a false northing of -5 000 000. Three Kort projections are for the islands Jutland, Sealand and Bornholm. kp2000j , kp2000s and kp2000b. The central meridians for this projections are 9.5°, 12° and 15° Longitude.

Estonia

The S42/59-EST is the old Datum S42 with anchor Point in Pulkovo and the Krassovsky 1940 ellipsoid. This Datum was former used in most countries of eastern europe. Zone 34 and zone 35 are the two Gauss Krüger 6° wide-projections, who cover the region in Estonia. The central meridians are 21° and 27° east Greenwich and there is a false easting of 500000 plus 4 or 5 * 10E6. One newer projection is the EST92-LB (L-EST) based on the ETRS89/GRS80 and is defined as a Lambert conformal conic projection with two standard paralells. The Baltic93 is a Tranversal Mercator projection for all three baltic states, it is like an UTM, but has the central meridian at 24° east of Greenwich and unlike in UTM y-axis is easting and x-axis is northing.

Latvia

LV-LKS-92 is the actual used projection system in Latvia and is similar with the Baltic93, but with a false northing of -6 Mio. meter.

Lithuania

The Datum LT-LKS94 is consistent with ETRS89 and the related Gauss-Krüger projection on the GRS80 with a scale of 0.9998. There is a false easting of 500000 meters and no false northing. The central meridian is also 24° east.

Poland

For Poland Pulkowo Datum S42/58 with the Krassovsky ellipsoid was former used. There are five projections, the projection I - IV are a stereographic projection and number V is a modified Gauss Krüger projection ( with a scale factor ? 1 ) for different regions in the country. The EUREF89 projections are Transversal Mercator projections with a special scale factor ( 0.999923 ) and central merdians at 15°, 18°, 21° and 24° are name zone 5,6,7,8 and have the false easting of 500000 plus zone-number * 10E6. Additional exist a TM projection named CS92 for whole poland. This one has its central meridian at 19° east and also a false northing of -5300000 meter. The EUREF89 refer to the ETRS89 ( with GRS80 ).

Hungary

HD72 ( Hungarian Datum 1972 ) has its anchorpoint in Szölöhegy, the used ellipsoid is a GRS67 [IUGG 1967] and there is one Oblique Mercator projection for the land. The name is EOV (Egyseges Orszagos Vetületi rendszer) with false northing and easting and a scale factor of 0.99993.

Romania

Dealul Piscului 70 is a Datum for Romania with the Krassovsky ellipsoid. It replaces the older Dealul Piscului 33 which has a little different fundamental point and uses the International 1924 ( Hayford ). And the two projections are Stereo 70 and Stereo 33, both an oblique stereographic projection with false northing (y) and easting (x) of 500000 meter. "Stereo 33" is the one with the Dealul Piscului 33 Datum. S42(ANCPI = Agentia Nationala De Cadastru Si Publicate Imobiliara) in combination with an oblique stereographic projection is a optimized projection for the romanian territory.

Greece

The GGRS87-Grid is a UTM-similar projection of the GGRS87 Datum with the fundamental point of Dionysos based on GRS80 ellipsoid. The central merdian is 24 ° east of Greenwich. The Datum Greek It was defined by information from Topography Department (National Technical University of Greece). For this region the ED50 with zones 35 and 36 was in use.

Italy

In Italy various systems are in use. So we have the Datum Monte Mario, which is also named ROMA40. The anchor point is Monte Mario ( Roma ) on the ellipsoid Hayford or International 1924. The geographic system ROMA40-Roma has the prime meridian through Monte Mario. For the mainland there are two projections for the western and eastern part. They have different central meridians and false easting values. For the islands Sardinia and Sicily other Datum transformation parameter are used. In Sardinia the zone west projection is used, in sicily the zone east. For Südtirol the Datum Roma40 with the Gauss-Boaga projection with false easting 500000 and false northing of -5 Mio. is in use. Another coordinate system for italy was the ED50 and the projections UTM32 - 34. The fundamental point for that is Potsdam, Helmert Tower and the ellipsoid is also Hayford/International. The newer coordinate systems are ETRS89 in combination with UTM.

Croatia

HDKS (or MGI1901) is the Datum used in Croatia. The anchor point is Vienna, Hermannskogel and the ellipsoid is the Bessel 1848. The zone 5 and 6 of the the Gauss Krüger projections are valid for the area. The central meridians are 15° and 18° and the false eastings are 500000 meter plus zone number * 10E6. There is a factor of 0.9999 but nofalse northing. The HTRS96-TM is a transverse mercator projection for the whole country, the central meridian is at 16°30', false easting is 500000 and its builded up on the HTRS96 (equivalent to ETRS89).

Slovenia

In Slovenia D48 is the geodetic datum. The anchor point is Vienna, Hermannskogel and the ellipsoid is the Bessel 1848. The zone Nr.5 cover the whole Land area and the false easting 500000 meter and false northings of -5Mio. are given. The central meridian is 15° east of Greenwich. The new realization of ETRS89 in Slovenia is the D96 and the projection system is the D96/TM. This have the same parameter like the old projection system.

This is only a very short overview about the circumstances, for more information about the coordinate systems in europe please see the explanations in national agencies, EU-CRS, Wikipedia ....