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Converting Land Registry (Easting and Northing) Co-ords to Lat/Long

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  • 09-01-2011 12:44pm
    #1
    Carlow52
    Closed Accounts Posts: 2,389 ✭✭✭


    here
    http://www.osi.ie/en/alist/co-ordinate-converter-tool.aspx
    I see a set of conversion routines
    • Irish Grid
    • ITM (Irish Transverse Mercator)
    • UTM (Universal Transverse Mercator)

    I have some Easting and Northing co-ords from a land registry print out which I want to convert for use in GPS.

    My guess is that the Land Registry stuff is based on the ITM and not the UTM system, I have established it is not the Irish Grid used on the Discovery Series of Maps

    Thanks


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    #2
    coylemj
    Registered Users Posts: 25,455 ✭✭✭✭coylemj


    According to the folks in OSi the Land Registry went digital with ITM in 2005.


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    #3
    Alun
    Registered Users Posts: 21,466 ✭✭✭✭Alun


    It's certainly not UTM, that's for sure, that's really only used by the military and in countries that don't have their own grid system.

    As far as distinguishing between ITM and IG, you should be aware that there is an alternative form of representing IG coordinates that does not use the grid letters commonly used on the OSi 1:50k series maps, but use a 6 digit easting and northing, the first digit of each effectively replacing the grid letter.

    For example, the GPO on O'Connell St. is at approx. the following coordinates ...

    315876 234626 (full 1m resolution IG)
    O 15876 34626 (full 1m resolution IG within grid square O)
    O 158 346 (100m resolution IG within grid square O, commonly used for outdoor navigation, hillwalking etc.)
    715820 734653 (full 1m resolution ITM)

    The so-called 'false origin' for ITM was deliberately chosen to be very different to that for IG so that no grid reference from the one system falls within the land mass of Ireland using the other system. I.e. if you were to take an IG grid reference and try to place it on a map using ITM it would place it somewhere in the Atlantic ocean, so it's easy to distinguish one from the other. If the first digits are <4 for easting and <5 for northing, they're IG, if they're more than that then it's ITM.

    BTW, if you go to http://maps.osi.ie/publicviewer you can view some quite detailed maps going right down to building and plot level. Down in the bottom left hand corner there's a box showing the X,Y coordinates of the cursor, which are also ITM coordinates if you want confirmation.


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