Re: [Qgis-user] about some ellipsoïdal distances

[G. Allegri]

Not at all.
The change has already been committed to the development version.

giovanni

2012/4/6 blavet <didier.blavet at ird.fr>

> **
> Thank you very much for this very fast and efficient diagnosis
>
> Best regards
>
> Didier Blavet
>
> Le 06/04/2012 12:01, G. Allegri a écrit :
>
> Probably I've found the bug.
> In Qgis the semi-minor axis of the ellipsoid is calculated with:
>
>  b = a - (f/a)
>
>  where
> b = semi-minor axis
> a = semi-majot axis
> f = inverse flattening
>
>  while it should be:
>
>  b = a - (a/f)
>
>
>  In Qgis the WGS84 semi-minor axis is 6378136,xxx
> while it should be 6356752.xxx
>
>  giovanni
>
>
>
>
>
> 2012/4/6 G. Allegri <giohappy at gmail.com>
>
>> AFAICS, the Qgis formula [1] to calculate distances on ellipssoid is
>> Vincenty's.
>> I've reproduced it for the first set of points and I can confirm tha QGis
>> gives 540.9973919726176 m
>>
>>  The online Vincenty calculator [2] gives 540.045 m
>>
>>  I suppose it's a rounding issue.
>> I will investigate it more...
>>
>>  giovanni
>>
>>
>>  [1]
>> http://trac.osgeo.org/qgis/browser/trunk/qgis/src/core/qgsdistancearea.cpp#L540
>>
>> [2] http://www.movable-type.co.uk/scripts/latlong-vincenty.html
>>
>>  2012/4/6 blavet <didier.blavet at ird.fr>
>>
>>>  Dear QGis Developpers and Users
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>>
>
> --
>
>
> _______________________________________________________________________________________
>
> *Didier B**lavet*
>
> Institut de Recherche pour le Développement - IRD (http://www.ird.fr)
>
> UMR Eco&Sols - Ecologie Fonctionnelle & Biogéochimie des Sols &
> Agroécosystèmes
>
> (Montpellier SupAgro-CIRAD-INRA-IRD) (
> http://www.montpellier.inra.fr/ecosols)
>
> Bâtiment 12, 2 place Viala, F-34060 Montpellier Cedex 2 , France
>
> Tel bureau : +33 (0)4 99 61 21 33
>
> Secrétariat : +33 (0)4 99 61 21 01 / Fax : +33 (0)4 99 61 21 19
>
> Courriel : didier.blavet at ird.fr
>
>
> _______________________________________________________________________________________
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