[PROJ] Danish_System_34_Sjaelland

[Thomas Knudsen]

That definition definitely looks odd. The correct EPSG id for System 34
Sjælland
is 10250 (and its companion for the western part of Denmark, "System 34
Jylland"
is EPSG:10160).

For historical reasons, those systems are utterly odd: They originated as
cadastral
systems, and the cadastre did not really care about the absolute
orientation of
the systems, hence ignoring (at that time, i.e. 1930-ish), existing
astro-geodetic
observations, to the effect that what was specified as a transverse cylinder
projection actually ended up as oblique.

Which also means, as noted by Mikael Rittri a decade ago on this mailing
list, that System 34 can be approximated at the metre level by an oblique
mercator
(proj=omerc).

The reconstructions we recently submitted to the EPSG, are based on
transverse
mercator, but use grid based datum shifts to correct for the
mis-orientation and
network tensions.


Den tirs. 15. aug. 2023 kl. 00.18 skrev Javier Jimenez Shaw <
j1 at jimenezshaw.com>:

> Hi
>
> I got this wkt, which projection "Transverse Mercator Sjaelland" is not
> supported by PROJ
>
> PROJCS["Danish_System_34_Sjaelland", GEOGCS["GCS_European 1950",
> DATUM["D_European 1950",
> SPHEROID["International_1924",6378388.000000,297.000000]],
> PRIMEM["Greenwich",0.000000], UNIT["Degree",0.017453292519943295]],
> PROJECTION["Transverse Mercator Sjaelland"],
> PARAMETER["Scale_Factor",0.999600],
> PARAMETER["Central_Meridian",9.000000],
> PARAMETER["False_Easting",500000.000000], UNIT["Meter",1.000000000000]]
>
> Seems to be something very Danish specific, and quite old. Do you know any
> equivalent wkt that may work in PROJ? There were some Danish grid files
> added recently for S34
>
> Thanks
> Javier
> .___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ... .... ._ .__
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