Irish grid reference system

As Irish Grid coordinate system used on the maps of Ireland is called. It is uniform in both the Republic of Ireland and in Northern Ireland application, but differs from National Grid of the UK Ordnance Survey.

Reference ellipsoid for the land surveying is the modified Airy ellipsoid. As a map projection is a transverse Mercator projection is used, the ( true ) origin lies at 53 ° 30 'N, 8 ° W. This source is a Cartesian coordinate system is defined. To avoid negative coordinates, 250 km will be added to all values ​​in an easterly direction ( " right value " ) 200 kms and to all values ​​in North direction ( " high- value"). Coordinate information is usually in meters, so that eg of origin referred to the coordinates 200,000 250,000 receives. ( The point with the coordinate 0 0 is also called "false origin " of the map projection. It is located southwest of the island. )

To get to something more manageable coordinates that map in grid squares of 100 km side length is divided, which are designated by the letters A to Z ( without the big I). Here, some of squares are outside of Ireland and are not used.

Within this 100 -km squares the mileage from 00 to 99 are numbered. For the nearest meter grid reference then a letter and two five-digit numbers are required.

Example: The Halfpenny Bridge is located in the WGS84 at 53 ° 20 ' 46.7 " N 6 ° 15' 47.1 " W. The Irish Grid is the 315 725 or 234 278 O 15725 34278th

Instead of such meter exact coordinates only one grid square is, in general, so O 15 34 ( within 1 km due ) or O 157 342 (just 100 m).