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

[G. Allegri]

I think we should normalize the list to avoid duplicated ellipsoids, which
is misleading to the user.

I guess multiple issues are crossing.

1 - problems with the ellipsoid definition causing wrong measurements
2 - problems with the list making the combo box not behaving correctly
(select WGS84 but Clark 1866 appears when reopening peoject properties)

giovanni


Il 21 ott 2017 20:47, "Régis Haubourg" <regis.haubourg at gmail.com> ha
scritto:

> 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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>
>
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