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    Re: NOW what?
    From: Gary LaPook
    Date: 2015 Aug 15, 18:08 +0000


    From: David Pike <NoReply_DavidPike@fer3.com>
    To: garylapook---.net
    Sent: Saturday, August 15, 2015 3:12 AM
    Subject: [NavList] Re: NOW what?
    Next time I'm in England I will stop by and visit( I now know where you live.) Or, I could call in a cruise missile strike.

    (It looks like you made a typing error with the second longitude.)

    gl
     
    My, you chaps must be fast readers.  Having just woken up, I’ve not had a chance to read the paper yet.  I’m not sure I’d understand it anyway, even if I take a couple of days over it.  However, I do live close to the Greenwich Meridian, so I thought it was worth taking some values.  Using Garmin GPS72H No3878260628 Mod state 2.80 I got my position at 07.27UTC on 15th August as N53 10.175  W000 32.244 using WGS84 datum.  At 07.29UTC my position in the same spot was N53 10.157 W000 32.244 using the datum the set named UK National Grid, which I assume is OSGB36 based on an Airy Spheroid, which is the nearest I could find to what surveyors were probably using at the time of the naming of the Greenwich Meridian.  The difference in longitude measured by me was:
     
    32.244'-32.148'=0.096’.   0.096’ of longitude at N53 10.157 = 0.96xcos53.169x1852m = 106m and yes you’d have to walk east to bring a GNSS set on WGS84 to read 000.00 at Greenwich
     
     I’m not sure yet if the paper is just about datum issues or something more complicated; it’ll take some deep reading.  However the important point is that if you’re relying on a GNSS set, and I’m told they works best when left set in WGS84 datum, you need to make sure that the coordinates requested are also WGS84 coordinates.  For most people this shouldn’t matter much, but for the military programming missiles and artillery and the like and for deep drafted vessels navigating narrow channels, it’s very important.   Dave (More a rule of thumb sort of Nav)


     


       
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