Re: Geodetic precision

From: Allen Thomson (
Date: Thu Aug 16 2001 - 12:57:14 PDT

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    > As a newcomer to the List, from the background of being a Geodesist,
    > I've been wondering about the apparent precision of some List members'
    > declared co-ordinates and to what geodetic framework they refer.
    A most interesting discussion.   In many cases, I suspect the
    answer to "which datum?" is "nary a clue."  In my own case,
    pre-NIMA and pre-Heavens Above, I scrounged coordinates
    from atlases, airport and weather site databases, wherever.
    Few if any of those gave the datum used.
    - Which datum is preferred today and should be used when possible?
    (I'd guess WGS84.)
    - If the datum is unknown, what level of accuracy should be reported and
    used?  I.e., where do the coordinates given in decimal degrees diverge
    in the commonly used systems?  The current standard in this community
    seems to be four places after the decimal point, 10 meters, around GPS
    accuracy.  Does that demand specifying the datum?
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