# Office of Geomatics: Origins of Selected Geodetic Datums

This information is presented for its historical interest and is not validated for official use. For a list of the latest validated datum transformation parameters and information about WGS 84, go to NGA Publications on Office of Geomatics. In particular, you may wish to compare the table below with TM8358.1 Table 1 Geodetic Datums Used in Map Production Page 1 and Page 2 .

The earth is not a sphere, but an ellipsoid of revolution, flattened slightly at the poles and bulging somewhat at the Equator. The ellipsoid is used as a surface of reference for the mathematical reduction of geodetic surveys.

A geodetic datum is the set of defining parameters (including the dimensions of the ellipsoid) which forms the basis for the computation of geodetic positions from horizontal control surveys.

The table below contains the origins of selected datums. See the footnotes that follow for additional information.

## Origins of Selected Geodetic Datums

Numbers in parenthesis refer to the footnotes that follow the table.

Datum

Area

Name of Point

Latitude

Xi

Longitude

Eta

EllipsoidNorth American 1927 North America Meades Ranch 39 13 26.686 N -1.32 98 32 30.506 W 1.93 Clarke 1866 Old Hawaiian Hawaii Oahu West Base Astro 21 18 13.89 N 0.00 157 50 55.79 W 0.00 Clarke 1866 Qornog Greenland Station 7008 64 31 06.27 N 0.00 51 12 24.86 W 0.00 International Hjorsey 1955 Iceland Hjorsey 64 31 29.260 N 0.00 22 22 05.840 W 0.00 International Provisional South American 1956 Venezuela, Ecuador, Peru, Bolivia, Chile La Canoa 08 34 17.17 N 2.42 63 51 34.88 W -0.55 International Corrego Alegre Brazil Corrego Alegre 19 50 15.14 S 0.00 48 57 42.75 W 0.00 International Chua Astro Paraguay Chua Astro 19 45 41.16 S 0.00 48 06 07.56 W 0.00 International Campo Inchauspe Argentina Campo Inchauspe 35 58 16.56 S 0.00 62 10 12.03 W 0.00 International Yacare Uruguay Yacare 30 35 53.68 S 0.00 57 25 01.30 W 0.00 International European Europe Potsdam, Helmertturm 52 22 51.446 N 3.36 13 03 58.741 E 1.78 International Odnance Survey of Great Britain 1936 Great Britain: Northern Ireland Royal Greenwich Observatory, Herstmonceux 50 51 55.271 N -1.14 00 20 45.882 E -2.2 Airy Ireland 1965 Ireland Royal Greenwich, Herstmonceux 50 51 55.271 N -1.14 00 20 45.882 E -2.2 Modified Airy (8) Merchich Morocco Merchich 33 26 59.672 N 0.00 07 33 27.295 W 0.00 Clarke 1880 (2) Voirol Algeria Voirol Observatory 36 45 07.9 N 0.00 03 02 49.45 E 0.00 Clarke 1880 (2) Adindan Sudan Adindan 22 10 07.110 N 2.38 31 29 21.608 E -2.51 Clarke 1880 (2) Sierra Leone 1960 Sierra Leone D.O.S. Astro SLX2 08 27 17.6 N 0.00 12 49 40.2 W 0.00 Clarke 1880 (2) Liberia 1964 Liberia Robertsfield Astro 06 13 53.02 N 0.00 10 21 35.44 W 0.00 Clarke 1880 (2) Ghana Ghana GCS Pillar 547 Accra 05 32 43.30 N 0.00 00 11 52.30 W 0.00 War Office (3) Nigeria Nigeria Minna 09 39 08.87 N 0.00 06 30 58.76 E 0.00 Clarke 1880 (2) Arc 1950 Africa (South of Equator) Buffelsfontein 33 59 32.00 S 3.46 25 30 44.622 E -0.88 Clarke 1880 (2) Tananarive (Antananarivo) Obsy 1925 Malagasy Rep. Tananarive (Antananarivo Obsy) 18 55 02.10 S 0.00 47 33 06.75 E 0.00 International World Geodetic System 1972 Sino-Soviet Bloc World Geodetic System 1972 Herat North Afghanistan Herat North Astro 34 23 09.08 N 0.00 64 10 58.94 E 0.00 International Indian India, Pakistan, Burma, Thailand, Southeast Asia Kalianpur Hill 24 07 11.26 N 0.31 77 39 17.57 E 0.00 Everest (5) Tokyo Japan Tokyo Obsy 35 39 17.515 N 0.00 139 44 40.502 E 0.00 Bessel Hu-Tzu-Shan Taiwan Hu-Tzu-Shan 23 58 32.340 N 0.00 120 58 25.975 E 0.00 International Luzon Philippines Balanacan 13 33 41.000 N 3.47 121 52 03.000 E (9) Clarke 1866 Kertau West Malaysia Kertau 03 27 50.71 N 3.47 102 37 24.55 E -10.90 Modified Everest (6) Timbalai East Malaysia Timbalai 05 17 03.548 N 0.00 115 10 56.409 E 0.00 Everest Djakarta Indonesia (Sumatra, Java) Butavia 06 07 39.522 S 0.00 106 48 27.79 E 0.00 Bessel Bukit Rirnpah Indonesia (Bangka) Bukit Rimpah 02 00 40.16 S 0.00 105 51 39.76 E 0.00 Bessel G. Serindung Kalimantan Ep. A 01 06 10.60 N 0.00 105 00 59.82 E 0.00 Bessel G. Segara Indonesia (Kalimantan, East) G. Segara (P5) 00 32 12.83 S 0.00 117 08 48.47 E 0.00 Bessel Montiong Lowe Indonesia (Sulawesi) Montiong Lowe (PI) 05 08 41.42 S 0.00 119 24 14.94 E Bessel Australian Geodetic Australia Johnston Memorial Cairn 25 56 54.5515S 7.68 133 12 30.0771E -4.19 Australian National (7) Geodetic Datum 1949 New Zealand Papatahi Trig Station 41 19 08.900 S -1.30 175 02 51.000 E (9) International Guam 1963 Marianas Islands Tagcha 13 22 38.490 N -10.35 144 45 51.560 E 24.12 Clarke 1866 Local Astrol World Geodetic System 1972 Camp Area Astro Antarctica Camp Area Astro 77 50 52.521 S 0.00 166 40 13.753 E 0.00 International Note: This table contains historic data that may not meet current standards.

## Footnotes for Origins of Selected Geometric Datums

- Xi and Eta are deviations of the vertical at the datum point.

Xi = deviation in the meridian = Ø_{A}= Ø_{G }Eta = deviation in the prime vertical = (Lambda_{A}= Lambda_{G }) COS Ø

Subscripts A and G refer to Astronomic and Geodetic values respectively. Latitude is reckoned positive northward and longitude is reckoned positive eastward.

- The dimensions of the Clarke 1880 spheroid adopted by different countries vary in accordance with which of Clarke's original dimensions are used: (a, b) or (a, f) or which foot-meter relationship is used to convert the units from feet to meters. In the area referenced to Arc 1950 datum, the dimensions adopted are:

Semimajor axis = a = 6 378 249.145 ... meters

Semiminor axis = b = 6 356 514.966 ... meters

The above figures yield:

Flattening = f = 1/293.46 63076 ...

In the areas of Merchich and Voirol datum, the dimensions adopted are:

a = 6 378 249.2 meters

b = 6 356 515.0 meters

the above figures yield:

f = 1/293.46 60208

The latter are the values adopted for construction of Department of the Army Universal Transverse Mercator and latitude function tables.

- Dimensions of the War Office Spheroid are:

a = 6 378 300.58 meters

f = 1/296

- The World Geodetic System 1972 (WGS 72)is not referenced to a single datum point. It represents an ellipsoid whose placement, orientation, and dimensions best fits the Earth's equipotential surface which, on the average, coincides with the geoid. The system was developed from a worldwide distribution of terrestrial and geodetic satellite observations. The dimensions of the WGS 72 ellipsoid are:

a = 6 378 135 meters

f = 1/298.26

- The dimensions of the Everest Spheroid are:

a = 6 377 276.345 meters

f = 1/300.8017

- The dimensions of the Modified Everest Spheroid are:

a = 6 377 304.063 meters

f = 1/300.8017

This spheroid has the same flattening as the Everest Spheroid, but a slightly larger axis (28 meters) because of the difference between foot-meter relationship used in Malaysia and the one used in India.

- The dimensions of the Australian Spheroid are:

a = 6 378 160 meters

f = 1/298.25

- The dimensions of the Modified Airy Spheroid are as follows:

a = 6 377 340.189 International meters

b = 6 356 034.448 International meters

the above figures yield:

f = 1/299.325

- Prime vertical deflection is unknown.

- Local Astros are several independently determined datum origins for surveys over small areas.

- A geodetic datum is defined by five parameters:

Geodetic latitude (Ø_{0}) at the origin

Geodetic longitude (Lambda_{0}) at the origin

Geoid height (N_{0 }at the origin

Dimensions of the Ellipsoid (2 parameters)

An initial geodetic azimuth at the origin may be defined rather than the longitude, but since the Laplace azimuth equation must be satisfied, there is no need to define both. In each of the datums listed, the geoid height at the origin is zero, except for Australia Geodetic Datum where it is 4.9 meters.

**Point of Contact:**Geospatial Science Division

Office of GEOINT Science

phone (314) 676-9123, DSN 846-9123

gandg@nga..mil

Document last modified April 29, 2013