[QGIS-Developer] problems with IGNF:ELG ellipsoids in srs.db

[Régis Haubourg]

Hi Nyall, a partial answer maybe.
IGNF is a registry from French National Geographic Institute. They have
brought their own registry into proj4, which is perfectly valid an
authorized, but obviously creates confusions for the same SRS available in
the EPSG registry. Moreove, most definitions are identical, except that the
IGNF adds a nad grid for a better precision.
>From what I see in the issue, some non IGNF definition also causes trouble,
when a and b parameter are set to zero. I think that this is more a QGIS
(or proj4?) issue than a problem with the projection list.
I would really like to know too when and how are the srs lists loaded in
QGIS.

Cheers
Régis

2017-10-21 2:10 GMT+02:00 Nyall Dawson <nyall.dawson at gmail.com>:

> On 19 October 2017 at 19:01, G. Allegri <giohappy at gmail.com> wrote:
> > Some measurement testing on QGIS 3.0 revealed that
> > https://issues.qgis.org/issues/13957 issue is still there, and it's
> quite
> > subtle because we have very similar elliposid names, with similar
> > definitions except IGNF:ELG ones have trailing zeros.
> >
> > For example WGS84:
> >
> > id     acronym            name      radius                     parameter2
> > ------------------------------------------------------------
> --------------------------------------
> > 41 WGS84             WGS 84  a=6378137.0          rf=298.257223563
> > 51 IGNF:ELG053   WGS84   a=6378137.0000    rf=298.2572235630000
> >
> > This is quite misleading for the user whene selecting the elliposid for
> > Measurements.
> > Anyway, it could be accepted if they both worked but in case ellispoid
> #51
> > is selected two problems appear:
> >
> > 1 - the selected ellipsoid is not retained in the dropdown box. If you
> > reopen project properties "Clarke 1866" is selected instead of "WGS84"
> > 2 - (maybe related to the latter) measure values are completely wrong
> >
> > Everything works fine if "WGS 84" (ellipsoid #41) is selected.
>
> I'm also curious about this  -  has anyone got any background on how
> the ellipsoid list has been generated and the rationale behind these
> inclusions?
>
> Nyall
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