PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
December 2016
919
by
Clifford J. Mugnier, CP, CMS, FASPRS
T
his month’s topic features both the Republic
of Ireland and Northern Ireland. The island
was invaded by the Celts around 500
BC
,
and was converted to Christianity in the 5
th
cen-
tury
AD
by Saint Patrick. Boundary maps in Ire-
land were made to accompany the “terriers” (prop-
erty records) of the surveys in 1636-40 by order
of Lord Strafford, Viceroy of Ireland. In 1654-59,
the “Down Survey” comprised maps of the “town-
lands” averaging 300 acres each and baronies to-
taling over two-thirds of the surface of Ireland,
about 20,000,000 acres. The Ordnance Survey
was established in 1791 to produce national map-
ping, this included all of Ireland. The need for an
accurate map of Ireland was brought to the fore in
the 1800’s by problems with a local tax, known as
the “County Cess.” In 1824, the committee chaired
by Thomas Spring Rice recommended to the (Brit-
ish) House of Commons that a survey of Ireland
was required to provide a definitive indication of
acreages and ratable values for the purpose of es-
tablishing local taxes in Ireland. That same year,
Colonel (later Major General) Thomas Colby of
the Ordnance Survey received orders to proceed
with the work of triangulation and Six Inch (6” = 1
mile) topographical surveys for all of Ireland.
“Reaction to the Engineers bythe local people was
mixed but generally they were regarded with suspicion.
A particular nuisance was the removal by local people
of the poles, set up as targets on mountains, before the
surveyors had a chance to observe them and, in one case,
the observers were attacked. However, by contrast,
in Glenomara, County Clare, the people climbed the
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 Ireland
was
originally printed in 1999 but contains updates to their coordinate
system since then.
mountain with them in a great crowd, with flutes, pipes
and fiddles, treating the building of the trigonometrical
station as a festive occasion.”
The initial baseline for the Irish surveywas selectedbyColby
at the Plain of Magelligan near Lough Foyle in Londonderry.
Colby decided to use the principle of compensation for the
manufacture of the baseline measuring apparatus. The
principle was to use two metal bars, one of brass and one of
iron, which were placed 11/8 inches apart but joined rigidly to
each other at their centers. The bars were allowed to expand
or contract freely, with pivoted steel tongues fixed to both
bars at their ends. These were marked with silver pins, and
although the length of the bars changed with temperature,
the distance between the two pins remained constant. Six
sets of bars were made, each just over 10 feet long. The
baseline of nearly 8 miles was measured over 1827-1828. The
Photogrammetric Engineering & Remote Sensing
Vol. 82, No. 12, December 2016, pp. 919–921.
0099-1112/16/919–921
© 2016 American Society for Photogrammetry
and Remote Sensing
doi: 10.14358/PERS.82.12.919
