Re: Geodetic precision - food for thinking

From: Joerg Kampmann (joerg.kampmann@ibk-consult.de)
Date: Thu Aug 16 2001 - 14:55:52 PDT

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```hi, this is really very interesting. e.g. when I quote my position I am
referring to Mapblast.com :-)
and I do not know the geoid they are using. our local maps say I am 60 m
above sea level ...

now: as you say the same location differs about 124 m according to
different géoids.

I am asking: what precision do we actually need here ? for the normal
observer - like me an "aficionado" - I think I do not really need the
referring geoid ...

but that may not be the case in every instance. But then we have some
real problems:
- the elsets what geoid do they require?
- how can we transform - in case we need that precision - data from one
geoid to the other in order to make data comparable ?

just food for thinking
Jörg

Allen Thomson schrieb:
>
> > 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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