![]() ![]() 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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