PE&RS November 2016 - page 843

PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
November 2016
843
by
Clifford J. Mugnier, CP, CMS, FASPRS
T
his month’s topic features the Republic of
Mauritius, an island nation in the Indian
Ocean that includes Rodrigues Island, the
Agalega Islands, and the Cargados Carajos Shoals
(Saint Brandon). Discovered by the Portuguese in
the early 16h century, Mauritius was occupied by
the Dutch from 1598-1710, and was held by the
French from 1715 until 1810 when it was captured
by the British. Mauritius was formally ceded to the
United Kingdom in 1814. It became independent in
1968, and became a republic in 1992. This nation
has a land area of 1,850 square kilometers, which
is almost 11 times the size of Washington, DC.
The first triangulation was carried out by the astrono-
mer, Monsieur L’Abbe La Caille (literally “Mister Abbot of
the Quail”), when he was sent to the island by the French
East India Company in 1753. He observed the position of his
observatory (Mabile’s house), which was situated 4,730 feet
east and 2,610 feet north of the Port Louis Time Ball, as: Φ
o
= 20° 09’ 42 South, Λ
o
= 55° 08´ 15˝ East of Paris. He de-
termined the summit of Le Pouce as one of approximately 90
stations. Note that “Le Pouce” literally means “the thumb” in
English, which is an apropos description of its shape! I guess
that the Grid system used by Lacaille (modern spelling) was
based on the Bonne projection, which was in vogue with the
French at that time. Unfortunately, the records of Lacaille’s
survey did not survive the ravages of time.
In 1874, Lord Lindsay led an ex- pedition to Mauritius to
observe the transit of Venus across the local me- ridian. The
purpose was to observe a network of precisely determined lon-
gitudes in the Indian Ocean. The points on Mauritius included
Belmont (primary), Pamplemousses, and Solitude. Others in the
network were the island of Rodrigues and the French islands of
Réunion and St. Paul. Interestingly, the datum origin in Egypt
(different British network and decade) is still named “Venus.”
THE REPUBLIC OF
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 Republic of Mauritius was
originally printed in 1999 but contains updates to their coordinate
system since then.
In 1876, the Surveyor General of the Colony of Mauritius,
M. Connal, published coordinates of the second triangulation
and used the Datum origin as Le Pouce, where: Φ
o
= 20° 11´
49.156˝ South, Λ
o
= 57° 31´ 39.60˝ East of Greenwich. The
ellipsoid of reference was the Bessel 1841 where the semi-ma-
jor axis (a) = 6,377,397.155 meters and the reciprocal of flat-
tening (
1
/
f
) = 299.1528128. This point was also the projection
origin of the first Cassini-Soldner Grid System of Mauritius,
and was used with a quadrant system (north- south, east-
west), rather than with the more “modern” False Eastings
and False Northings.
In 1902, Captain Harrison of the British Colonial Survey
Section produced a series of “1 inch” (to the mile) maps also
using Le Pouce as the origin, but based on the Clarke 1858 el-
lipsoid. Harrison’s mapping, presumably also using the Cas-
sini- Soldner Grid, was based on two net- works of triangula-
Photogrammetric Engineering & Remote Sensing
Vol. 82, No. 11, November 2016, pp. 843–845.
0099-1112/16/843–845
© 2016 American Society for Photogrammetry
and Remote Sensing
doi: 10.14358/PERS.82.11.845
819...,833,834,835,836,837,838,839,840,841,842 844,845,846,847,848,849,850,851,852,853,...906
Powered by FlippingBook