[Qgis-user] bessel ellipsoid 1841

[G. Allegri]

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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