PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
June 2016
403
by
Clifford J. Mugnier, CP, CMS, FASPRS
T
his month’s topic features the Cayman
Islands of the Caribbean Sea. The islands
of Grand Cayman, Cayman Brac, and Little
Cayman comprise this dependency of the United
Kingdom. Columbus visited the islands in 1503,
but the Spanish never settled there. The Cayman
Islands (including Jamaica) were ceded to Britain
in 1670 under the Treaty of Madrid. Later, the
islands were colonized by settlers from Jamaica
and remained a parish of Jamaica. In 1962, when
Jamaica became independent, the Cayman Islands
became a “direct” British Dependent Territory.
Property “Platt Books” (sic) were the first recorded land
grants of land ownership on Grand Cayman (five parcels), and
are dated 1730 and 1740. The Royal Navy performed its original
hydrographic survey of Grand Cayman Island in 1773. In 1835,
CaptainOwen,R.N. determinedthe longitudedifferencebetween
Fort George (Grand Cayman) and Morro Light, Havana Cuba.
Captain Owen’s survey produced the first Admiralty Chart
of all three islands. Finlay’s North Atlantic Directory of 1895
differed with that longitude by 49 seconds, and the discrepancy
continued unresolved for 60 years. The difference was reflected
between the Admiralty Chart No. 462 and the U.S. Army
Map Service (AMS) 1:50,000 topographic maps of the islands.
The AMS maps were based on the U.S. Naval Hydrographic
Office Chart No. 0043 (20th) edition of 1933. H.M.S. Vidal, a
hydrographic survey ship initiated a new survey in September
1954. The following month, using a geodetic astrolabe, Captain
Owen’s “Observation Spot” was validated to within 20 feet. The
coordinates of the first Cayman Island geodetic datum, “Fort
George Observation Spot 1835 Datum” are based on the Origin:
F
o
= 19
o
17´ 48.01˝ North,
L
o
= 81
o
23´ 05.83 West of Greenwich.
The original datum was the basis of the Admiralty Chart No.
462, and was centered on the ruins of the old Fort George in
THE
The Grids & Datums column has completed an exploration of
every country on the Earth. For those who did not get to enjoy
this world tour the first time,
PE&RS
is reprinting prior articles
from the column. This month’s article on the Cayman Islands was
originally printed in 1998 but contains updates to their coordinate
system since then.
Georgetown. Furthermore, a new “Observation Spot” was
obtained by that astrolabe determination:
F
o
= 19
o
17´ 45.02˝
North,
L
o
= 81
o
23´ 06.83 West of Greenwich and was the basis
of the new edition of Admiralty Chart No. 462 for the plan of
Georgetown Anchorage.
The current reference system for the island of Grand
Cayman was originally set by the Inter American Geodetic
Survey (IAGS). It was lost for a number of years after a road
was built over it, but was recovered in 1995. GC 1 1959 Datum
is based on the Origin:
F
o
= 19
o
17´ 54.43˝ North,
L
o
= 81
o
22´
37.17 West of Greenwich, with the defining orientation based
on the azimuth from GC 34 to GC 10 being 334
o
13’ 25.97”.
The datum is referenced to the Clarke 1866 ellipsoid. The
scale was established by Tellurometer, a brand of electronic
distance meter (EDM) invented and built in South Africa
that uses microwaves rather than the currently more popular
type of gizmo that uses Infra-Red (IR) light. The datum was
established for the subsequent photogrammetric mapping
Photogrammetric Engineering & Remote Sensing
Vol. 82, No. 6, June 2016, pp. 403–404.
0099-1112/16/403–404
© 2016 American Society for Photogrammetry
and Remote Sensing
doi: 10.14358/PERS.82.6.403
