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 Geospatial Sciences. 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 |
Ellipsoid |
North 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.
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