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Thank you very much for this very fast and efficient diagnosis<br>
<br>
Best regards<br>
<br>
Didier Blavet<br>
<br>
Le 06/04/2012 12:01, G. Allegri a écrit :
<blockquote
cite="mid:20120406100114.222F4A9A574@fx404.security-mail.net"
type="cite">Probably I've found the bug.
<div>In Qgis the semi-minor axis of the ellipsoid is calculated with:</div>
<div><br>
</div>
<div>b = a - (f/a)</div>
<div><br>
</div>
<div>where </div>
<div>b = semi-minor axis</div>
<div>a = semi-majot axis</div>
<div>f = inverse flattening</div>
<div><br>
</div>
<div>while it should be:</div>
<div><br>
</div>
<div>b = a - (a/f)</div>
<div><br>
</div>
<div><br>
</div>
<div>In Qgis the WGS84 semi-minor axis is 6378136,xxx</div>
<div>while it should be 6356752.xxx</div>
<div><br>
</div>
<div>giovanni</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
<br>
<div class="gmail_quote">2012/4/6 G. Allegri <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:giohappy@gmail.com">giohappy@gmail.com</a>></span><br>
<blockquote class="gmail_quote"
style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div class="im"><span>AFAICS, the Qgis formula [1] to calculate
distances on ellipssoid is Vincenty's.</span>
<div>I've reproduced it for the first set of points and I can
confirm tha QGis gives 540.9973919726176 m</div>
<div><br>
</div>
<div>The online Vincenty calculator [2] gives 540.045 m</div>
<div><br>
</div>
<div>I suppose it's a rounding issue. </div>
<div>I will investigate it more...</div>
<div><br>
</div>
<div>giovanni</div>
<div><br>
<div><br>
</div>
<div>[1] <a moz-do-not-send="true"
href="http://trac.osgeo.org/qgis/browser/trunk/qgis/src/core/qgsdistancearea.cpp#L540"
style="color: rgb(17, 85, 204);" target="_blank">http://trac.osgeo.org/qgis/browser/trunk/qgis/src/core/qgsdistancearea.cpp#L540</a> </div>
<div>[2] <a moz-do-not-send="true"
href="http://www.movable-type.co.uk/scripts/latlong-vincenty.html"
style="color: rgb(17, 85, 204);" target="_blank">http://www.movable-type.co.uk/scripts/latlong-vincenty.html</a> </div>
</div>
<br>
</div>
<div class="gmail_quote">2012/4/6 blavet <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:didier.blavet@ird.fr"
target="_blank">didier.blavet@ird.fr</a>></span><br>
<blockquote class="gmail_quote"
style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div>
<div class="h5">
<div text="#000000" bgcolor="#ffffff">Dear QGis Developpers and
Users <br>
<br>
<br>
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<p style="margin-bottom: 0cm;"><font>_______________________________________________________________________________________</font></p>
<p style="margin-bottom: 0cm;"><font color="#008000"><font><b>Didier
B</b><b>lavet</b> </font></font>
</p>
<p style="margin-bottom: 0cm;"><font color="#000000"><font>Institut
de
Recherche
pour le Développement - IRD (<font color="#0000ff"><a
moz-do-not-send="true" href="http://www.ird.fr" target="_blank">http://www.ird.fr</a></font>)
</font></font></p>
<p style="margin-bottom: 0cm;"><font color="#000000"><font>UMR
Eco&Sols - Ecologie Fonctionnelle & Biogéochimie des Sols &
Agroécosystèmes </font></font>
</p>
<p style="margin-bottom: 0cm;"><font color="#000000"><font>(Montpellier
SupAgro-CIRAD-INRA-IRD)
(<font color="#0000ff"><a moz-do-not-send="true"
href="http://www.montpellier.inra.fr/ecosols" target="_blank">http://www.montpellier.inra.fr/ecosols</a></font><span
style="font-style: normal;">)</span></font></font></p>
<p style="margin-bottom: 0cm;"><font color="#000000"><font>Bâtiment
12,
2
place Viala, F-34060 Montpellier Cedex 2 , France </font></font>
</p>
<p style="margin-bottom: 0cm;"><font color="#000000"><font>Tel
bureau : <a moz-do-not-send="true"
href="tel:%2B33%20%280%294%2099%2061%2021%2033" value="+33499612133"
target="_blank">+33 (0)4 99 61 21 33</a> </font></font>
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<p style="margin-bottom: 0cm;"><font color="#000000"><font>Courriel
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href="mailto:didier.blavet@ird.fr" target="_blank">didier.blavet@ird.fr</a></font>
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<p style="margin-bottom: 0cm;"><font size="2">_______________________________________________________________________________________</font></p>
<p style="margin-bottom: 0cm;"><font color="#008000"><font size="2"><b>Didier
B</b><b>lavet</b> </font></font>
</p>
<p style="margin-bottom: 0cm;"><font color="#000000"><font size="2">Institut
de
Recherche pour le Développement - IRD (<font color="#0000ff"><a class="moz-txt-link-freetext" href="http://www.ird.fr">http://www.ird.fr</a></font>)
</font></font></p>
<p style="margin-bottom: 0cm;"><font color="#000000"><font size="2">UMR
Eco&Sols - Ecologie Fonctionnelle & Biogéochimie des Sols &
Agroécosystèmes </font></font>
</p>
<p style="margin-bottom: 0cm;"><font color="#000000"><font size="2">(Montpellier
SupAgro-CIRAD-INRA-IRD)
(<font color="#0000ff"><a class="moz-txt-link-freetext" href="http://www.montpellier.inra.fr/ecosols">http://www.montpellier.inra.fr/ecosols</a></font><span
style="font-style: normal;">)</span></font></font></p>
<p style="margin-bottom: 0cm;"><font color="#000000"><font size="2">Bâtiment
12,
2 place Viala, F-34060 Montpellier Cedex 2 , France </font></font>
</p>
<p style="margin-bottom: 0cm;"><font color="#000000"><font size="2">Tel
bureau : +33 (0)4 99 61 21 33 </font></font>
</p>
<p style="margin-bottom: 0cm;"><font color="#000000"><font size="2">Secrétariat
:
+33 (0)4 99 61 21 01 / Fax : +33 (0)4 99 61 21 19 </font></font>
</p>
<p style="margin-bottom: 0cm;"><font color="#000000"><font size="2">Courriel
:
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