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IG vs ITM co-ordinates

  • 24-08-2012 6:06pm
    #1
    Irish Stones
    Registered Users, Registered Users 2 Posts: 2,308 ✭✭✭


    Hello to everybody,
    I'm a new user to this forum. I'm Italian, so forgive my possible mistakes.
    I know that this matter has already been discussed before, but I find it hard to catch some details.
    I understand that there's a transition from the old IG co-ordinates system to the ITM and that the latter is much more precise than the other.
    I also found a page for the conversion, this one
    http://www.osi.ie/calculators/converter_index.asp

    What I can't understand is how the results of the conversions form this page can be used.
    For istance, from one of the pages of the Megalithomania.com website I take this co-ordinates
    Longitude W 006° 16' 29.5"
    Latitude N 53° 15' 26.5"
    The same page has the following additional data
    ITM East 480366
    ITM North 584435
    GPS reading O 15115 24387

    If I type the geographic co-ordinates into the boxes from the osi webpage above, and hit the "convert" button, the numbers that I get are much different
    ITM East 715105.5
    ITM North 724389.5

    These numbers are much more similar to the GPS reading (that is what I could read from a OSI Discovery Map) than to the ITM numbers from the Megalithomania page. I guess that those numbers have been read from the display of a GPS receiver whose units are set to Irish Grid ITM.

    Can anybody clear this matter for me, please?
    Thanks a lot!


Comments

  • #2
    muckish
    Registered Users, Registered Users 2 Posts: 610 ✭✭✭muckish


    Looks like the ITM readings on the megalith page are just wrong.


  • #3
    Irish Stones
    Registered Users, Registered Users 2 Posts: 2,308 ✭✭✭Irish Stones


    How can it be that the owner of the website didn't realize of that?
    I mean, I just took a random page from that site, but all pages that I checked have the same errors.
    I can't believe that he misread his GPS receiver all those times.
    Couldn't there be another explanation?
    I'm not doubting your words, I'm just asking ;)


  • #4
    muckish
    Registered Users, Registered Users 2 Posts: 610 ✭✭✭muckish


    Ok I think I have this sorted.
    If you notice the ITM coordinates are the same for EVERYTHING in the database so they must have done one conversion and it got copied into all the records.
    Every monument in megalithomania has the same ITM coordinates
    ITM East 480366
    ITM North 584435

    A pretty basic lazy mistake.

    Interestingly though this ITM coordinate is the summit of Carrauntoohil, the highest summit in Ireland. Not even a monument in the database for it.


  • #5
    Irish Stones
    Registered Users, Registered Users 2 Posts: 2,308 ✭✭✭Irish Stones


    Wow! Great job you did!
    It seems I was as lazy as the website owner because I didn't take the time to compare other pages to the first one, I only saw they were all wrong.
    So we can say that the conversion done by the osi website is correct.
    I find it weird that a professional man like the website owner (who has been running that website for 10 years now) made such a big mistake, but he did it.
    Thanks so much for your support and time in this matter, you cleared a big doubt of mine!
    Go raibh maith agat! ;)


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