Russell,
Up until the introduction of GPS and the resulting trend towards the use of
satellite datum WGS 84, the majority of north sea oilfield operators used
UTM zone 30 (central meridian 3 deg E) projection, European Datum 1950
(ED50) the latter being based upon the 1924 International spheroid which is
identical to the Hayford 1909 spheroid with a semi-major axis (a) of
6378388 metres and an inverse flattening (1/f) of 297.0.
You can find UTM zone 30 (ED50) as one of the built-in projection/datums in
MapInfo.
Regrettably many organisations conducting work and publishing data in the
early days of the North Sea did not always clearly define the datum,
ellipsoid & projection used. I have come across work which was projected
using UTM, but based upon WGS72 datum and elipsoid rather than
ED50/International.
Some operators (principally Shell) adopted a Transverse Mercator projection
which used a central meridian of 0 degrees, as this gave rise to less
distortion in mapping their areas of operation which straddled 0 degrees.
The projection parameters were the same as those for UTM, but with a
non-standard CM, and ED50 was used as the datum. You would have to set up a
custom projection for this one.
One point to be aware of which may or may not be of significance. A lot of
early North Sea work used the Transit satellite system either as a primary
position sensor or as a calibration reference. This system was understood
to use the WGS 72 datum, and published transformation parameters were
widely used to transform to ED50. It subsequently came to light that the
ephemiris data broadcast by the Transit satellites was actually based upon
NWL 9D rather than WGS 72. Around 1982, following investigations by the
survey organisations of the 6 nations around the North Sea, UKOOA adopted a
set of transformation parameters between the actual broadcast satellite
ephemiris (NWL 9D) and ED50. These transformation parameters differed from
those previously in general use, and to distinguish co-ordinates computed
using this transformation they were defined as ED50 (Common Offshore). By
my recollection, the upshot of this was position differences of the order
of 7 - 10 metres between the two systems. In mapping contexts this is not
generally an issue, but it can crop up if comparing well positions from
earlier and more recent data.
Hope this helps,
Andy Beckett
-----Original Message-----
From: Lawley, Russell S [SMTP:[EMAIL PROTECTED]]
Sent: 03 April 2002 11:59
To: MapInfo-L (E-mail)
Subject: MI-L projections /datums suitable for UK onshore/offshore
available in Mapinfo
Hi,
I have a query, For the UK I happily use British National grid or OSGB36 or
UTM zone30N (wgs84 ellipsoid) projections. What other UK-suitable
projections /datums are there in Mapinfo? I have several hardcopy maps
(circa 1960-1970s) that indicate they are projected as UTM using the
international ellipsoid 1924 (sometimes called the Hayford 1909
ellipsoid??)
I need to capture these maps for digital archiving. What parameters will i
have to enter into my mapinfo projection/ datum files to emulate these? Is
it just a matter of editing of editing the UTMWGS parameters to use the
Int.
1924 parameters? any help greatly appreciated..will sum..
Russell Lawley
Geoscientist
British Geological Survey
www.bgs.ac.uk
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