[Qgis-user] bessel ellipsoid 1841

[Torsten Lange]

Sorry for responding so late and thank you for all of the hints!

I was a bit misled and nervous about using a coordinate system that has 
something "unknown" in its definition... :)

Torsten

Am Dienstag 27 September 2011, 17:46:12 schrieben Sie:
> Just a side note: the Bessel ellipsoid isn't a datum by itself. A datum is
> defined by an ellipsoid, it's point of origin and various ancillary data
> about its oriantation and, generally, by a geodetic network that realizes
> it.
> 
> 2011/9/27 Barend Köbben <kobben at itc.nl>
> 
> > FYI, the proj string does have a datum, one based on the Bessel ellipsoid
> > (which is a datum), but I agree with giovanni that the proj=longlat is
> > unlikely to be correct for your map. Neighbouring Netherlands uses the
> > Bessel datum, and a double stereographic projection (It's epsg:28992).
> > But also it is doubtful that was used in the 19th century (sorry).
> > Nowadays Germany uses Gauss-Kruger, Münsterland would be in EPSG
> > Projection 31466 - DHDN / 3-degree Gauss-Kruger zone 2 ...
> > 
> > 
> > 
> > --
> > Barend Köbben
> > ITC - University of Twente, Faculty of Geo-Information
> > Science and Earth Observation
> > PO Box 217, 7500AE Enschede (The Netherlands)
> > +31-(0)53 4874 253
> > 
> > On 26-09-11 23:02, "G. Allegri" <giohappy at gmail.com> wrote:
> > >It's quite unlikely that an earth centred datum has been used for your
> > >map, and the 4004 should only be used when the datum is unkonwn and we
> > >suppose that the ellipsoid origin is the earth centre... yet I don't
> > >know what the geodetic reference(s) was used in Germany along the 19th
> > >century.
> > >
> > >giovanni
> > >
> > >
> > >
> > >2011/9/26 Torsten Lange <tlange at gwdg.de>
> > >
> > >
> > >Hello,
> > >
> > >I have a historical map from 1855 from the Muensterland Basin, Germany.
> > >The
> > >map shows geographic coordinates, thus my colleague said most likely
> > >it's Bessel 1841 ellipsoid.
> > >
> > >QGis offers:
> > >Unknown datum based upon the Bessel 1841 ellipsoid EPSG:4004
> > >+proj=longlat +ellps=bessel +no_defs
> > >
> > >Why there is no datum? Shouldn't there be one?
> > >
> > >Thank you, Torsten
> > >_______________________________________________
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> > 
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