676
November 2018
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
= 10° 37´ 33.412˝ N,
λ
=61° 22´ 30.920˝ W. The triangulation
then proceeded southwards to the Harmony Hall Base Line; a
discrepancy being computed through the unadjusted triangu-
lation of 8.4 inches was equal to nearly 1/11,500
th
part of the
Harmony Hall Base. Latitude was determined at both bases
by meridian altitudes of North and South stars, and the re-
sults showed reasonable agreement. Azimuth was also deter-
mined at both bases by observation of circumpolar stars at
and near elongation. The adjustment of the triangulation of
Trinidad was carried out by the usual approximate methods.
The triangulation of Tobago was carried out by Capt. G.M.
Latham, R.E., and a party of the Royal Engineers in 1923.
A base with a mean distance of 2,162.3741 ft. (
sic
) (~659 m)
was determined from three measurements with the Trinidad
Base Measurement Apparatus. The main net of the Tobago
triangulation was adjusted by the method of least squares.
“In 1925, on the advice of the Colonial Survey Committee,
it was decided to adopt the Cassini Projection for Trinidad
maps. A suitable sheet system based on a grid for the whole
island has been evolved. The projection used for both Trin-
idad and Tobago is the Cassini, Clarke (1858) Spheroid. In
Trinidad, the Standard Meridian is Long. 61° 20´ 00˝ and the
point of Origin is situated as Lat. 10° 26´ 30˝ on that me-
ridian, the Rectangular Coordinates of this point for conve-
nience are called N. 325,000 links and E. 430,000 links. In
Tobago, the Standard Meridian is Long. 60° 41´ 09.632˝ W
and the point of Origin (Mount Dillon, Trig Sta. L.) is situ-
ated as Lat. 11° 15´ 07.843˝ N on that meridian, the Rectan-
gular Coordinates of this point for convenience are called N.
180,000 links and E. 187,500 links. ——o0o—— Brigadier H.
St. J. Winterbotham, C.M.G., D.S.O., 15 October 1930.” Note
that 8,000 links = 1 mile, and 1 meter = 4.971014137 links.
Also, for the Clarke 1858 ellipsoid as used in Trinidad and
Tobago: a = 6,378,293.6 meters and
1
/
f
= 294.26. The origin
of the Old Trinidad Datum of 1903 is defined at the Harbour
(
sic
) Master’s Flagstaff where:
Φ
o
= 10° 38´ 39.02˝ North,
Λ
o
= 61° 30´ 38.00˝ West of Greenwich, and the corresponding
Cassini-Soldner Grid coordinates are: N.436,366.91 links,
E.333,604.30 links.
According to John W. Hagar, “In 1942 the Coast & Geodetic
Survey put out Tables for Computation of Plane Coordinates
on Lambert Grid: Trinidad. I would guess that these were
part of the general contingency planning of WW II. Anyway,
they are Lambert, Clarke 1866, yard, latitude of origin = 10°
25´ north (lower standard parallel = 10° 10´ north, upper
standard parallel = 10° 40´ north), longitude of origin = 61°
30´ west, scale factor = 0.99999054, FE = 120,000 yards. I
don’t have a false northing but cannot conceive of a U.S. mil-
itary grid without same. Never saw any maps or coordinates
on this system.”
Just across the Gulf of Paria, Ing. Dr. Adolfo C. Romero
initiated the redefinition of classical triangulation for the
northern expanses of the South American continent. The
small Venezuelan town of La Canoa, just a few hundred
miles from Trinidad was used as the origin of the Provisional
South American Datum of 1956 (PSAD 56) where:
f
= 08° 34´
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