ORDNANCE SURVEY OF NORTHERN IRELAND®
Geodetic Infrastructure
In
order to undertake accurate surveys, OSNI has established and maintains the geodetic infrastructure
in Northern Ireland. This is the survey control network, or skeleton, on which the mapping of
Northern Ireland hangs. It provides a cohesive framework that enables positions within Northern
Ireland to be determined accurately, and allows surveys and mapping to be correctly related through
the use of a common reference system.
In support of the Geodetic
Infrastructure, and to enable access to accurate survey control, OSNI provides the following information
and services:
Geodetic Information
•
Details of the Coordinate Reference Systems in use in Northern Ireland
Traditional
survey
control information
• Irish Grid coordinates and descriptions
are available for triangulation
points.
• Benchmark descriptions and values are available
to allow determination of
heights above Mean Sea Level Belfast.
GPS survey control information
•
For surveyors using GPS, a Network of Active and Passive GPS sites have been established to provide
high absolute positioning accuracy throughout Northern Ireland.
•
In areas where additional
survey control is required, a service is available to undertake local GPS surveys and establish control
as required.
Transformations & Geoid Model
•
Formulae and parameters
have been developed to allow coordinates to be transformed between Irish Grid and the European Terrestrial
Reference System (ETRS89).
• The OSGM02 geoid model has been
developed to allow levels
to be transferred between GPS derived ellipsoidal heights and Belfast datum.
•
Software
is available to help carry out these transformations.
