# Re: [OpenMap Users] MGRS grid square less than 100 km

From: Don Dietrick <dfdietrick_at_gmail.com>
Date: Thu, 8 Sep 2011 15:27:20 -0400

Hi Mike,

The grid squares always represent 100km. It might be easier to
visualize the zones as representing 6 degrees horizontally. Since
that doesn't map perfectly to meters, some parts of the squares will
fall outside of that 6 degree zone. So if you were going to convert a
decimal degree lat/lon to MGRS, you would end up in the neighboring
zone, even though that coordinate was still in the A column of 100km
grid squares.

The OpenMap code should get you to the proper lat/lon decimal degree
location given the relative MGRS coordinates of neighboring zones -
however, if you then use MGRSPoint to go to decimal degree lat/lon,
you'll end up with the MGRS coordinate in the correct zone for that
lat/lon.

There are different rules for the zones around Norway, but MGRSPoint
should handle those, too.

Hope this helps,

Don

On Wed, Sep 7, 2011 at 2:01 PM, Farwell, Michael D - GS
<MICHAEL.FARWELL_at_itt.com> wrote:
> All,
>
>
>
> I’m new to MGRS and OpenMap, so please bear with me:
>
>
>
> Does the OpenMap MGRSPoint class take into account MGRS grid squares that
> are less than 100 km?  For example, UTM zones at the equator are 666 km
> wide.  The 1N zone has 8 columns A-H.  B-G cover a full 100 km.  A and H are
> incomplete and cover approximately 33 km each.  This information is from the
> following website
> (http://www.andrewlesley.freeserve.co.uk/gps/UTMMGRS.html).  Also, the
> picture showing the MGRS grid of Honolulu on Wikipedia seems to back up this
> information.
>
>
>
> The following code produces 100000 and 200000:
>
>
>
> MGRSPoint mgrsp = new MGRSPoint("1NAA");
>
> System.out.println(mgrsp.easting);
>
>
>
> mgrsp = new MGRSPoint("1NBA");
>
> System.out.println(mgrsp.easting);
>
>
>
> I would expect it to produce 100000 and 133000.  Hopefully, I’m wrong and my
> understanding of MGRS is incorrect, but I need help understanding the
> discrepancy I’m seeing.  Thanks.
>
>
>
> Mike Farwell
>
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Received on Thu Sep 08 2011 - 15:29:00 EDT

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