Re: Geodetic precision

From: Chris Olsson (
Date: Sun Aug 19 2001 - 14:46:19 PDT

  • Next message: Chris Olsson: "Re: Geodetic precision"

    Joerg Kampmann asks:
    >can you tell me how I find out the datum which Mapblast uses here in Europe??
    I've taken a look at MapBlast, Joerg , and it appears to me that they use
    whatever local datum was originally used in the maps which they buy.  For
    example, a few test points in the UK show that their co-ordinates there are
    good to the fifth decimal place of Lat/Long degrees and that they are using the
    Airy spheroid and the OSGB36 datum.  It is clear that they have not converted
    to WGS84.  From this, I surmise that their policy is to leave all datasets in
    their original national mapping datum.
    For most countries, there is usually only one national mapping datum.  Germany
    is slightly problematic when trying to guess which "standard" datum is being
    used.  This is partly because of the autonomy of individual Bundesländer, but
    also because of the considerable turbulence in Germany's 20th century history.
    The invading US occupation troops imposed the Hayford spheroid and devised what
    became called the ED50 datum.  In the East, the "other side" imposed the
    Krasovski spheroid and the Pulkovo datum.  Meanwhile, the natives had their own
    favoured geodetic framework which is based on the Bessel spheroid and the
    Rauenberg datum.
    My initial guess would be that the dataset is expressed in the Bundesamt für
    Kartographie und Geodäsie's favoured geodetic framework which is, I believe,
    the Rauenberg/Potsdam datum on the Bessel 1841 spheroid.
    Perhaps an email to the cartographers at MapBlast might elicit the information
    which you seek, Joerg?
    Cheers,        Chris Olsson
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