PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
October 2016
763
computation of all the classical geodetic datums of Western
Europe after the war, and the resultant coordinate system
was termed the European Datum of 1950 (ED50). AMS
directed the computations by initially computing common
points between Belgium and France in 1945. The Belgian
stations consisted of Arlon Church, Anlier, Bouillon,
Willerzie, Rulles, Bon Secours, Mont Sainte Genevieve,
and Mont Kemmel. The French stations were Aumets,
Tellancourt, and Sighy-Mont Libert. The computations
consisted of a least squares polynomial solution of the
coordinates of the respective stations as computed on the
conformal plane represented by the UTMGrid, International
(Hayford) ellipsoid. The coefficients that were determined
in Washington by AMS for these junction points were used
to transform the respective interior points to ED50, with
UTM used as the unifying connection tool for these two
countries. The rest of Western Europe followed with French
datum connections being the initial governing factor for the
remaining countries. The ED50 remained a NATO military
secret for some years. Belgium continued with independent
observations, and established a new provisional adjustment
for the country. The two Vlaanderen provinces, the northern
half of Brabant, Antwerpen, and Limburg provinces were
essentially held fixed from 1940. The southern provinces of
Hainaut and Namur had minimal changes in coordinates,
and the region in between received the major adjustment.
The Kingdom then published the Belgian 1950 Datum with
the “KM” Lambert 50 Grid, all of the Belgian 1927 defining
parameters remaining unchanged.
New instruments and re-observations required another
adjustment a couple decades later, and the Belgian Datum
of 1972 is defined by the origin at the geodetic monument
d’Uccle: Φ
o
= 50
o
47´ 57.704˝ North, Λ
o
= 04
o
21´ 24.983˝
West of Greenwich. The azimuth was from d’Uccle to Kester:
α
o
= 262
o
08´ 37.95˝. The International ellipsoid continued
to be used, and the only change for the new Lambert 72
Grid was that the new central meridian matched the new
datum origin (
l
o
= Λ
o
). Note that the plane coordinates for
the Lambert 72 Grid are considerably different from the
Lambert 50 Grid. The ellipsoid is defined to be tangent
with the geoid at d’Uccle. The vertical datum, “Deuxieme
Nivellement General” (DNG) was established at Oostende
by conventional tide gauge observations. Curiously, the
DNG is based on Mean Low Water and therefore is -2.33
meters with respect to local mean sea level.
The Readjustment of the European Triangulation
Network (RETrig) has been involved for decades as an
international cooperative effort that started with ED50.
The latest fruit of their labors is the ED87 adjustment
that is quite comprehensive and remarkably accurate.
The Royal Observatory of Belgium is now operating four
permanent GPS reference stations, and the accuracies of
these observations are now at the sub-centimeter level.
The stations are Brussels, Dentergemand, Dourbes, and
Waremme.
U
pdate
The Belgian Institut Géographique National has published
a PDF document in
French
that addresses the approved
transformation parameters
from
a UTM Grid on either
the EU50 Datum or on the WGS84 Datum
to
Projection
Lambert 72 or
to
Projection Lambert 50. See:
. Page 12
of the document has an easy-to-understand flow chart.
The contents of this column reflect the views of the author, who is
responsible for the facts and accuracy of the data presented herein. The
contents do not necessarily reflect the official views or policies of the
American Society for Photogrammetry and Remote Sensing and/or the
Louisiana State University Center for GeoInformatics (C
4
G).
This column was previously published in
PE&RS
.
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