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Grids & Datums COLUMN

The Kingdom of Belgium

The contents of this column reflect the views of the au- Many countries in Europe followed After WWII, the Kingdom of Bel- thor, who is responsible for the facts and accuracy of the French preference for the Bonne, gium adopted the Lambert Conformal the data presented herein. The contents do not neces- in spite of the fact that it is a miser- Conic Projection and defined the new sarily reflect the official views or policies of the Ameri- able projection for large-scale military grid such that the False Easting = 150 can Society for Photogrammetry and Remote Sensing and civilian engineering applications. km and the False Northing = 5,400 km and/or the University of New Orleans. The Bonne projection tables were easy at latitude 50o 30' North. The Belgian to compute on the ellipsoid. That ad- Lambert “KM” Grid had a Northern This month’s topic features the King- vantage apparently helped to keep it Standard Parallel of (f ) = 51o 10' dom of Belgium, the birthplace of N popular, in addition to the prestige af- North, a Southern Standard Parallel of Mercator, which gained its indepen- forded by adopting the same system as (f ) = 49o 50' North, and a Central Me- dence from the Netherlands in 1830. S used by the French. ridian ( ) = 4o 22' 04.71" West of Famous Belgian place names have be- lo After the “Great War” (WWI), the Greenwich. Note that the Belgians de- come prominent in many battles, in- Kingdom modified the Grid such that fined their Lambert Zone with two cluding Waterloo and part of the Battle the False Easting = 150 km and the standard parallels, which is the defi- of the Bulge. Triangulation was origi- False Northing = 120 km. The “New nition method favored by the French nally carried out by Snellius (1617), Convention” Bonne Grid (1919-1950) and the Americans. The British prefer Cassini (1745-48), and General had a Latitude of Origin (f ) = 50o 24' to use a Latitude at Origin ( ) and a Krayenhoff (1802-11). Although large- o fo North, and a Central Meridian ( ) = 4o Scale Factor at Origin ( ). The two scale topographic coverage dates back lo fo 22' 05.91" West of Greenwich. In post- methods of zone definition use to 1744, the organized national map- war years, the Belgians continued to slightly different formulae to produce ping was carried out by the military re-observe and re-adjust their triangu- the identical projection in most cases. “Depot de la Guerre,” originally lation network. In 1924, the Interna- The U.S. Army Map Service (AMS) founded in 1831. This national map- tional Conference of Geodesy and Geo- organized the re-computation of all ping organization has gone through a physics which conferred in Madrid, the classical geodetic datums of West- number of name changes until becom- adopted the Hayford ellipsoid as the ern Europe after the war, and the re- ing a civilian agency in 1976 with the new standard. The Belgians adopted sultant coordinate system was termed present name of “Institut Geogra- this new reference ellipsoid for their the European Datum of 1950 (ED50). phique National de Belgique” (IGNB). new Belgian Datum of 1927 with the AMS directed the computations by The classical first-order triangula- origin altered to the astronomical val- initially computing common points tion of Belgium was carried out be- ues of Lommel Signal at: = 51o 10' between Belgium and France in 1945. tween the years 1851 and 1873, when Fo 08.092" North, = 04o 22' 05.91" West The Belgian stations consisted of 84 primary stations were established. Lo Arlon Church, Anlier, Bouillon, The Observatoire Royale d’Uccle Da- of Greenwich. The azimuth was from Willerzie, Rulles, Bon Secours, Mont tum of 1884 was based on the origin of Lommel Signal to Lommel Turm: ao = o Sainte Genevieve, and Mont Kemmel. the old Brussels Observatory: = 51o 186 58' 47.05". During WWII, the Fo The French stations were Aumets, o connection between the New Triangu- 10' 06.895" North, Lo = 04 22' 05.89 lation of France (NTF) Datum and the Tellancourt, and Sighy-Mont Libert. West of Greenwich, and the ellipsoid Belgian Datum of 1927 was accom- The computations consisted of a least of reference was the “Carte de France” plished in 1940 by considering the squares polynomial solution of the co- (Delambre 1810). The triangulation geodetic differences in longitude. The ordinates of the respective stations as was dependent on two measured bases longitude difference between the me- computed on the conformal plane rep- at Lommel and Ostend with Beverloo ridians of Brussels and Paris, as deter- resented by the UTM Grid, Interna- as a base of verification. The ellipsoi- mined by a comparison of the two tri- tional (Hayford) ellipsoid. The coeffi- dal Belgian Bonne Grid was used with angulations through Mont Kemmel, cients that were determined in this datum from 1884 to 1919 with no gave the geodetic longitude of Brussels Washington by AMS for these junction False Easting or False Northing, and as 04o 22' 12.7". The observed astro- points were used to transform the re- was later referred to as the “Old Con- nomical difference between Brussels spective interior points to ED50, with vention” Grid. The lack of a false ori- and Greenwich was not used. This UTM used as the unifying connection gin is typical for late 19th century grid discrepancy was one of the major fac- tool for these two countries. The rest systems, and is a common theme tors that prompted the recomputation of Western Europe followed with found in European and colonial grids of all geodetic control in Western Eu- French datum connections being the of that era. Negative grid coordinates rope after the war. The Bonne Grid initial governing factor for the remain- (in the appropriate quadrants) were “New Convention” is also referred to ing countries. The ED50 remained a accepted as a normal way of doing as the “Orange Report Net Grid” and NATO military secret for some years. things. Note that the Bonne projection was used through WWII until 1950. Belgium continued with independent is an authalic (equal-area) projection.

CLIFFORD J. MUGNIER

956 October 1998 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING

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COLUMN

observations, and established a new at the geodetic monument d’Uccle: DNG is based on Mean Low Water and provisional adjustment for the coun- o o therefore is -2.33 meters with respect Fo = 50 47' 57.704" North, Lo = 04 try. The two Vlaanderen provinces, 21' 24.983" West of Greenwich. The to local mean sea level. the northern half of Brabant, azimuth was from d’Uccle to Kester: The Readjustment of the European Antwerpen, and Limburg provinces o Triangulation Network (RETrig) has ao = 262 08' 37.95". The International were essentially held fixed from 1940. ellipsoid continued to be used, and been involved for decades as an inter- The southern provinces of Hainaut the only change for the new Lambert national cooperative effort that started and Namur had minimal changes in 72 Grid was that the new central me- with ED50. The latest fruit of their la- coordinates, and the region in between ridian matched the new datum origin bors is the ED87 adjustment that is received the major adjustment. The quite comprehensive and remarkably (lo = Lo). Note that the plane coordi- Kingdom then published the Belgian nates for the Lambert 72 Grid are con- accurate. The Royal Observatory of 1950 Datum with the “KM” Lambert siderably different from the Lambert Belgium is now operating four perma- 50 Grid, all of the Belgian 1927 defin- 50 Grid. The ellipsoid is defined to be nent GPS reference stations, and the ing parameters remaining unchanged. tangent with the geoid at d’Uccle. The accuracies of these observations are New instruments and re-observa- vertical datum, “Deuxieme Nivelle- now at the sub-centimeter level. The tions required another adjustment a ment General” (DNG) was established stations are Brussels, Dentergemand, couple decades later, and the Belgian at Oostende by conventional tide Dourbes, and Waremme. Datum of 1972 is defined by the origin gauge observations. Curiously, the ......

PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING October 1998 957