18
January 2014
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
Miguel Trovoada as the new president in April of that year.
Elections in 2001 brought Fradique de Menezes to power.
De Menezes pledged to use revenues from increased tourism
and exploitation of the country’s newly discovered offshore
oilfields to improve the standard of living and modernize the
islands’ infrastructure. Grand changes seemed imminent. But
complications with extracting the oil in addition to possible
overestimations of the oil deposits have delayed economic
progress, and there is a palpable growing restlessness in the
deeply indebted and impoverished nation. A brief and bloodless
coup attempt was peacefully resolved in 2003 while the
president was out of the country. De Menezes was re-elected in
2006 in internationally observed, peaceful elections. São Tomé
presently scrapes by on US$25 million a year of foreign aid and
US$5 million in cocoa exports”
(Lonely Planet, 2013)
.
São Tomé and Príncipe is the smallest country in Africa,
being more than five times the size of Washington, D.C. It
has zero land boundaries, its coastline is 209 km long and is
measured from claimed archipelagic baselines with a territorial
sea of 12 nautical miles. The terrain is volcanic, mountainous
and the lowest point is the Atlantic Ocean (0 m); the highest
point is Pico de São Tomé (2,024 m).
(World Factbook, 2013)
In 1915, Admiral Gago Coutinho was Chief of the Geodetic
Mission of São Tomé and Príncipe. Since 1898 he had
lived for 20 years in the African bush, sleeping in camping
tents, working for boundary demarcations and geodetic
triangulations in Timor, Moçambique, Angola, and São Tomé.
His triangulation reconnaissance related by him was that
“it was necessary to use techniques similar to navigation
like to set a course with the compass, … recognize land and
make observations with the sextant at the top of the trees,
to sound, …, to find the most highest and suitable point.” In
1909 the Colonial Office of Portugal ordered 4 theodolites
from Filotécnica Salmoiraghi under specifications by Gago
Coutinho. To provide the highest accuracy the horizontal
circle was to be covered and the scales were to be engraved
in platinum to avoid the oxidation of the African climate.
During the first field campaign, Gago Coutinho noticed that
the instrument was far from ideal, its principal defects being
the ocular thumbscrew and the circles which at the time
were very difficult if not impossible to engrave accurately.
Some improvements made them operational and were being
used in the São Tomé and Príncipe Geodetic Mission (1915-
1917), also directed by Gago Coutinho, and the first Cape
Verde geographical mission (1918-1921). To scale the geodetic
network, a 10 km baseline was measured every 200 km.
Coutinho was the first Portuguese Surveyor to use invar wires,
and the most used lengths were 8 m, 24 m, and 48 m. He
found that after 10 years of use, the invar wires reached their
final lengthening of a third of a millimeter. Using appropriate
procedures the possible accuracy was 1/1,000,000.
(Geodetic
Field Operations for Cartography – an Overview Over the First
Portuguese Geodetic Mission in the Colonial Territories 1907-
1910, Paula Santos and Ana Roque, FIG 29 May, 2012)
It is thought that the São Tomé Datum origin is at
triangulation station Fortaleza where: Φ
o
= 00º 20’ 49.02” N,
Λ
o
= 06º 44’ 41.85” E and is referenced to the International
1924 ellipsoid where:
a
= 6,377,388 m and 1/
f
= 297. The
Príncipe Datum origin is at triangulation station Morro do
Papagaio where: Φ
o
= 01º 36’ 46.87” N, Λ
o
= 07º 23’ 39.56”
E and is also referenced to the International 1924 ellipsoid
(Limits in the Seas No. 98 - São Tomé and Príncipe, U.S.
Dept. of State, November 1, 1983)
.
However, according to John W. Hager, “São Tomé (code
PST) at Pico São Tomé is at latitude, φ
o
= 00° 16’ 10.72”
E, longitude, λ
o
= 06° 32’ 48.953” E, azimuth, α
o
= 223° 33’
26.903” to Mukinkí, Clarke 1866
(where a = 6,378,206.4 m ,
1/f = 294.9786982 – Ed.)
, altitude, H
o
= 2,023.74 meters. Astro
latitude is Φ
o
= 00° 16’ 19.0”. International ellipsoid values are
latitude, φ
o
= 00° 16’ 10.74” E, longitude, λ
o
= 06° 32’ 48.97”
E.
References: Ilha De. S. Tomé Resultados Finais 1915-1918,
Gago Coutinho, (Carlos Viegas), Capitão de Mar e Guerra,
Lisboa, 1920. International Hydrographic Bureau Special
Publication No. 24c, Geographic Positions, p. 52, Monaco,
January 1951. The IHB cites Clarke 1866 to 1951. Maps of
1957 (and later) are on International. IHB also gives azimuths
to (2) Mukinkí, (1) Fortaleza, (19) Ponta-Furada, and (7) Rôlas.
“Now for Principe. Morro do Papagaio (code MDP) at
Morro do Papagaio is at latitude, φ
o
= 01° 36’ 46.87 N,
longitude, λ
o
= 07° 23’ 39.65” E, azimuth, α
o
= 183° 11’ 59.62”
± 0.26” Abade to Ponta Capitão from south, International
ellipsoid, altitude, H
o
= + 680.45.
Reference: Triangulaçã e
levantamento da carta da Ilha do Príncipe; Longitudes em s.
Tomé; Megnetismo, Lisboa, 1934.
“Google Earth is a bust – mostly clouds. If I remember
correctly, the 1:25,000 topographic maps (dated 1957) of
São Tomé show a large amount of narrow gauge railroads.
They are located in the cocoa plantations and went up and
down hills. In some places they were connected by zig-zag
lines which indicated that they were too sinuous to map. I
couldn’t locate any examples on the imagery. Re the 1:25,000
maps I mentioned earlier, map grid - Projection: Mercator
Ellipsoid: International Origin: São Tomé, latitude 00° 16’
10.74” n, longitude 6° 32’ 48.97” E False Northing = False
Easting = 0
. n.b.
north and east are negative. I can’t make
sense of my notes. I also have the latitude of origin as the
mid-latitude of the area, that is, 00° 12’ 00.00” N. This gives
an origin value of N = 29,816.61 and E= 0. My suspicion is
that the map sheets had the grid and geographic values of the
control printed on them. If only ... I also have a note sheet for
Principe but no information. Suspicion, again, that I expected
a similar grid there but did not have the time to get a map
sheet from the library and analyze it.
JWH
.”
Current aeronautical information states that the
international airports are on the WGS84 Datum
.
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).
