The Spire of Dublin example provides a fix for a location that is accurate to 1 metre. The equivalent Irish Grid co-ordinate for the same location is: The second figure is the northing and puts the location 734,697 metres north of the false origin (along the Y axis) The first figure is the easting and means that the location is 715,830 metres east from the false origin (along the X axis). The ITM co-ordinate for the Spire of Dublin on O'Connell Street is: The easting and northing are in metres from the false origin. The first number is always the easting and the second is the northing. While OSi and OSNI intend to supply map information in the older Irish Grid format into the future, the Irish Institution of Surveyors has recommended that ITM be adopted as soon as possible as the preferred official co-ordinate system for Ireland.Īn ITM co-ordinate is generally given as a pair of two six-digit numbers (excluding any digits behind a decimal point which may be used in very precise surveying). This was done by shifting the ITM false origin further into the Atlantic and thereby creating substantially different co-ordinate numbers for any given location. As a result ITM coordinates had to be obviously different so users would not confuse the two. ITM and the older more established Irish Grid will (initially at least) be used in parallel.

A customised Transverse Mercator projection was chosen. The new system needed to satisfy various criteria: GPS compatibility, map distortion for the whole island of Ireland had to be minimal, it was to be conformal and backward compatible with existing mapping.

While the existing UTM co-ordinate system partly fulfilled the requirement for direct GPS compatibility it had some drawbacks, including varying levels of distortion across the island due to the central meridian being at the west coast of Ireland. The more precise the GPS measurements were, the more the translation process introduced inaccuracies.

The older Irish grid reference system required GPS measurements to be 'translated' (using co-ordinate transformations). The name is derived from the Transverse Mercator projection it uses and the fact that it is optimised for the island of Ireland. It was implemented jointly by the Ordnance Survey Ireland (OSi) and the Ordnance Survey of Northern Ireland (OSNI) in 2001. Irish Transverse Mercator ( ITM) is the geographic coordinate system for Ireland. An illustration of ITM coordinates over a map of Ireland.

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