PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
November 2018
677
17.170˝ N,
λ
= 63° 51´ 34.880˝ W. The ellipsoid of reference
is the International (Hayford 1909 or Madrid 1924) where
a = 6,378,388 meters and
1
/
f
= 297. Earlier work in Venezu-
ela had made connections to the island of Trinidad through
the assistance of the Inter American Geodetic Survey (IAGS),
and classical triangulation on the Loma Quintana Datum
of 1911 was extant across the Gulf of Paria. The PSAD 56
coordinates were subsequently also carried over to Trinidad
through the redefinition by Dr. Romero, the IAGS and the
U.S. Army Map Service.
The basic triangulation net of Trinidad and Tobago began
to be reobserved and adjusted by approximate methods in
1963-1965. The U.S. Army Topographic Command accom-
plished a subsequent simultaneous least-squares adjustment
of triangulation and traverse through the “USHER” comput-
er program for horizontal control surveys using the Varia-
tion of Coordinates method. This is known as the Naparima
Datum of 1972. The point of origin is station Naparima Hill
where:
f
= 10° 16´ 44.8600˝ N,
l
= 61° 27´ 34.6200˝ W, and
the ellipsoid of reference is the International. When I visited
Trinidad, I inquired where exactly the station on Naparima
Hill was located. I was told that it was about 20 meters past
the cliff face in thin air. It seems that there was a rock quarry
on the western face of the hill, and the station was blasted
away shortly after the last observation period in the early
1960s. For comparison, the Trinidad Datum of 1903 coordi-
nates for Naparima are:
f
= 10° 16´ 37.737˝ N,
l
= 61° 27´
31.489˝ W, H = 586 ft. Although the UTM Grid was adopted
for use with the new Datum, local use of the Cassini Grids on
the former Datum continued for various applications. These
applications included the contractual description of offshore
petroleum concessions (“Lease Blocks”) and reporting regu-
lations. As of 1999, the Cassini-Soldner Grid of Trinidad on
the Old Trinidad Datum of 1903 was alive and well in the “oil
patch.”
In 1996, the U.S. National Geodetic Survey (NGS) made
GPS observations of many countries in the Caribbean. Ob-
servations on the island of Trinidad included two points that
happened to be on both the Old Trinidad Datum of 1903 and
on the Naparima Datum of 1972. Thanks to David Doyle of
NGS, I received the WGS84 coordinates of all stations ob-
served. I performed a simple three-parameter analysis of
those two points and derived the following relations: FromOld
Trinidad 1903 To WGS 84,
Δ
X = –33.250 m,
Δ
Y = +232.675
m,
Δ
Z = +484.542 m, the fit was good to about 2 meters in
each component for the two points computed. From Napari-
ma 1972 To WGS 84,
Δ
X = +0.332 meters,
Δ
Y = +369.359
meters,
Δ
Z = +172.897 meters, and the fit was good to better
than a meter in each component for the two points computed.
In 1986 I was retained to study the relations of the various
Grids and Datums of the area, and I traveled to the islands
and mainland to research the original data. In 1987 I was
invited to present the results of my analysis and develop-
ment of the 7-parameter Bursa-Wolf Datum Shift relations of
all coordinate systems in the Republic of Venezuela and the
Republic of Trinidad and Tobago to the Minister of External
Affairs (Secretary of State) in Port of Spain. A new Interna-
tional Boundary Treaty was subsequently signed and ratified
by both republics. The defining Datum in the Treaty was the
PSAD 56. Next month I’ll write on Venezuela and I shall list
the various transformations among all four of the classical
Datums of the region that includes Trinidad and Tobago.
U
pdate
The government of Trinidad and Tobago has implemented a
network of GPS Continuously Operating Reference System
(CORS) sites in the two-nation republic. As of around 2007,
five sites had been installed, four on Trinidad and one on To-
bago. At the time of publication, a Virtual Reference System
had not been yet implemented, but it is likely in operation by
2018, (
A New Geodetic Infrastructure for Trinidad and
Tobago, Miller, K., Leon, T., Clarke, S., 14 pages, avail-
able for download from ResearchGate.net.
) There have
been some narratives from government publications avail-
able over the internet that some local cadastral surveyors
have been retracing original property boundary lines using
old Naparima Datum coordinates that are recoverable in lo-
cal areas but without coordination with other local cadastral
surveyors that used other Naparima Datum coordinates re-
covered in adjoining areas with failures to tie because of geo-
detic distortions inherent in the Naparima Datum. Although
observations of these discrepancies have been published over
the internet, there appears no publications that address any
solutions other than the new CORS system that may ignore
old positions to the benefit to independent surveys anew.
With a relatively new system of land registration for squat-
ters being implemented with state-of-the-art GPS position-
ing, the new cadastral system may indeed succeed in spite
of ignoring the geodetic history of the islands. Time will tell
after more news of developments and local innovations are
published in the open literature.
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
.
