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Calculating the GPS opposite

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  • 14-09-2015 9:14am
    #1
    54and56
    Registered Users Posts: 7,664 ✭✭✭


    Hi all,

    Is there a formula or a website which will calculate the opposite point on the planet to a particular GPS location e.g. 53.286288, -6.241409 (53°17'10.6"N 6°14'29.1"W) which is a random spot I just picked in Dundrum, Co Dublin?

    My kid wondered out loud the other day about what the opposite point on the planet is to our house. It would be interesting to know that and to see it on Google Maps.


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    #2
    Alun
    Registered Users Posts: 21,464 ✭✭✭✭Alun


    For Latitude simply change the sign, + to -, or vice versa. For Longitude subtract it from 180 degrees taking note of the sign, so -6 -180 = -186, or +6 - 180 = -174 for example.

    Or go here ...

    http://www.ubasics.com/dighole/

    Basically from Dundrum you'll end up in the Pacific Ocean!


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    #3
    54and56
    Registered Users Posts: 7,664 ✭✭✭54and56


    Alun wrote: »
    For Latitude simply change the sign, + to -, or vice versa. For Longitude subtract it from 180 degrees taking note of the sign, so -6 -180 = -186, or +6 - 180 = -174 for example.

    Or go here ...

    http://www.ubasics.com/dighole/

    Basically from Dundrum you'll end up in the Pacific Ocean!

    Thanks Alun, that's a really useful resource. I'll show it to the kids tonight.

    I don't live far from Dundrum so yep, middle of the Pacific ocean is where the opposite of our house is. That's the end of that little adventure.


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    #4
    BarryD
    Closed Accounts Posts: 2,917 ✭✭✭BarryD


    I think this may depend on how rigorous you require your answer to be. The concept of lat/long essentially describes a sphere whereas the earth is not a true sphere but an oblate spheroid, if I recall correctly from days of study on such matters? There's a whole science behind map projections and ways of representing the earth in mathematical shapes and terms. These shapes only approximate, closely but not exactly to the real shape of the earth.


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    #5
    Alun
    Registered Users Posts: 21,464 ✭✭✭✭Alun


    That's true, but trying to take into account the true shape of the earth in such calculations would be a bit OTT.

    For what it's worth, the "equation" I gave is still valid even for the reference ellipsoids such as WGS84 used for real world mapping.


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    #6
    Tabnabs
    Moderators, Recreation & Hobbies Moderators, Sports Moderators Posts: 15,710 Mod ✭✭✭✭Tabnabs


    BarryD wrote: »
    I think this may depend on how rigorous you require your answer to be.

    You'll still end up in the pacific ocean though. It's not like you can "fudge it" and end up in Australia...


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    #7
    BarryD
    Closed Accounts Posts: 2,917 ✭✭✭BarryD


    Tabnabs wrote: »
    You'll still end up in the pacific ocean though. It's not like you can "fudge it" and end up in Australia...

    Oh true and yes OTT, but in truth if you navigated to the spot given by the simple answer above and waited for the hypothetical drill bit to emerge from the sea, I suspect you'd find it some little distance away. How far away, I haven't possibly got the time or inclination to attempt to calculate!!


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