On Mon, 17 Oct 2022, Greg Troxel wrote:
Andrew C Aitchison <and...@aitchison.me.uk> writes:
I do know that 4326 uses a geoid which is less accurate *over Great
Britain* than the one the Great Britain Ordnance Survey have been
using for a century or two (OSGB36 Datum 1936, Airy Spheriod 1830!).
I suspect that other national geo-organisations do the same thing and
you will lose the extra accuracy in standardising on one coordinate
system over Europe.
I don't follow this at all. EPSG:4326 is a 2D system, so it doesn't
even have height, and has no associated geoid.
Ah. I misremembered; I should have said the GRS80 ellipsoid:
https://en.wikipedia.org/wiki/Ordnance_Survey_National_Grid#Compatibility_with_related_systems
The Airy ellipsoid is a regional best fit for Britain; more modern mapping
tends to use the GRS80 ellipsoid used by the Global Positioning System
(the Airy ellipsoid assumes the Earth to be about 1 km smaller in diameter
than the GRS80 ellipsoid, and to be slightly less flattened).
I do remember mourning that GPS overthrew the Airy Spheroid.
--
Andrew C. Aitchison Kendal, UK
and...@aitchison.me.uk
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