164
March 2019
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
reciprocal of flattening
1
/
f
= 293.465. Angola’s southern bor-
der is with that country once called German Southwest Afri-
ca, and Namibia is the only country in the African continent
to utilize the Bessel 1841 ellipsoid for its Schwarzeck Datum
where, for Namibia, the semi-major axis
a
= 6,377,483.865 In-
ternational meters and the semi-minor axis
b
= 6,356,165.383
International meters. Values actually used in Namibia are
a
= 6,377,483.865 legal meters and
1
/
f
= 299.1528128. The
origin point is Schwarzeck, near Gobabis, where
F
o
= 22° 45´
35.820˝ South, and
L
o
= 18° 40´ 34.549˝ East of Greenwich.
(Our Paul M. Hebert School of Law here at Louisiana State
University is helping build a Law Library at the University
of Namibia).
The earliest geodetic observation in Angola is to the 1884
meridional distance from the mid-Atlantic island of St. Hele-
na to Baie dos Elefantes (Elephant Bay) in Angola and thence
north to São-Paulo de Loanda (Luanda). This revealed a prob-
able error between 6´ and 6½´ in longitude in the existing
Portuguese charts. This error was again reported in 1888 in
a “Hydrographic Note” using meridional distances from Cape
Town Observatory to the two ports mentioned above and to
Moçãmedes. In 1891,
A
nnales
H
ydrographiques
of the French
Navy published the telegraphic determination of longitudes
for three sites in Angola as determined by Commander Pul-
len of the Royal English Navy. Those determinations were
São-Paulo de Loanda – at the pavilion slab of the Fort of San
Miguel –where
F
o
= 08° 48´ 24˝ South,
L
o
= 10° 53´ 05˝ East
of Paris, Benguela – at the Bureau Télégraphique (Telegraph
Office) – where
F
o
= 12° 34´ 43˝ South,
L
o
= 11° 03´ 40˝
East
of Paris
, and Moçãmedes – at the pavilion slab of Ponta da
Noronha – where
F
o
= 12° 34´ 43˝ South and
F
o
= 11° 03´ 40˝
East of Paris.
In 1918, the Portuguese authorities established a new posi-
tion for Luanda Observatory and supplied details of the trian-
gulation of that area. “A Missão Geográfica de Angola criada
na …,” “The Geographic Mission of Angola was created in the
province in 1921 to establish a geodetic net in order to provide
for a cartographic survey of the territory; after more than three
campaigns, when it was dissolved, the Mission had surveyed
two arcs of triangulation – one from Benguela to Huambo and
the other along the” (
meridian
) “14° 00´ East of Greenwich
from adjacent figures to Lubango. Subsequently, for geodet-
ic operations, a hydrographic mission, which had campaigns
from 1930 to 1933, established geodetic figures along the Zaire
(Congo) River with common vertices with the Congo (Kinshasa)
Triangulation, and executed a geodetic base with astronomical
observations for latitude in eight stations, for longitude in five
stations, and two for azimuth. Furthermore, the systematic
and regular occupation of geodetic points in the province was
initiated in the beginning of 1941 as an actual activity of the
Geographic Mission of Angola.
The instructions were formulated by the “Junta de Inves-
tigações do Ultramar” (Overseas Research Commission) of
which the following points, with respect to the geodetic ac-
tivities, were
1. complete the geodetic coverage of the province, includ-
ing the principal triangulation figures and the secondary
triangulation, first to involve two arcs of the meridian
and the parallel at a 2° interval, and second, to densify
adequately for cartographic operations at comprehensive
spaces in the principal triangulation figures;
2. establish geodetic bases at distances of about 400 km
along principal figures, and provide for the distribution
that forms a precision of European second-order triangu-
lation – which is a precision less than attributed to the
principal triangulation;
3. observe Laplace stations at 200-km by 200-km spacings;
4. obtain the following precision for the geodetic and astro-
nomic observations as principal triangles –6˝, secondary
triangles – 10˝, latitude – 0.2˝, longitude – 0.5˝, and azi-
muth – 0.5˝.” To paraphrase, the Chief of the Geographic
Mission later sent instructions in 1946 to observe arcs
of the meridian and the parallel at a multiple interval
of 3°. In 1953, the first order triangulation was adjusted
using tables from the U.S. Coast and Geodetic Survey
(
based on the Clarke 1866 ellipsoid
). “This adjustment
was based on the condition equations formed by 269 tri-
angles.”
The triangulation eventually comprised 17 bases at Qui-
mongo, Congo Yala, Quitinda, Luanda, Lucala, Camacupa,
Catumbela, Alto Catumbela, Cimo, Serpa Pinto, Quipungo,
Moçãmedes, Humbe, Baia dos Tigres, Sare, Namatuco, and
Luiana – determined 1722 points based on observations of
3809 triangles of which 856 points were not occupied – made
astronomical observations of latitude, longitude, and azi-
muth at 15 station – and performed the leveling of 943 km.
Immediately prior to WWII, the Belgians published book-
lets in French and Flemish, listing the coordinates and geo-
detic positions for Bas-Congo that extended from the Atlantic
Ocean to Leopoldville. In those booklets are some 38 points
that are referred to the Congo-Yella Datum. Some of those
points are Portuguese control points common with Angola
that shares the river. The fundamental point for the Con-
go-Yella Datum is the east base terminal of Congo-Yella
where
F
o
= 06° 00´ 53.139˝ South,
L
o
= 12° 58´ 29.287˝ East
of Greenwich, and the ellipsoid is Clarke 1880. Transforma-
tion parameters from the Congo-Yella Datum to the Angola
Datum (also Clarke 1880) are
D
X = –35.08 m,
D
Y = +184.83
m, and
D
Z = +63.02 m (±3.7 m); and from Congo-Yella Datum
to the Camacupa Datum of 1948 are
D
X = –44.47 m,
D
Y =
+179.47 m, and
D
Z = +59.30 m (±2.0 m). The similarity of
values gives confirmation that, in this region, the Angola Da-
tum is equivalent to the Camacupa Datum of 1948. From the
Congo-Yella Datum to the WGS 84 Datum,
D
X= –93.28 m,
D
Y= –164.11 m, and
D
Z= –169.02 m (±5 m). Grids based on
the Congo-Yella Datum are the Belgian Congo Gauss-Krüger
Transverse Mercator Fuseau 13 (Zone 13) where latitude of
origin (
j
o
)= 2° 30´ South, Central Meridian (
l
o
) = 13° E, FN =
700 km, FE = 220 km, and the scale factor. (m
o
) = 1.0; Fuseau
14 where latitude of origin (
j
o
) = Equator, Central Meridian
