Thanks Jan and Mikael for your responses. <br>As suggested, I have forwarded this bug to the QGIS developer mailing list.<br><br>Thibaut.<br><br><br><div class="gmail_quote">2010/1/21 Jan Hartmann <span dir="ltr"><<a href="mailto:j.l.h.hartmann@uva.nl">j.l.h.hartmann@uva.nl</a>></span><br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div bgcolor="#ffffff" text="#000000"><div class="im">
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On 21-Jan-10 12:52, Mikael Rittri wrote:
<blockquote type="cite">
<div dir="ltr" align="left"><span><font face="Arial">Jan Hartmann wrote: </font></span></div>
<div dir="ltr" align="left"><span></span> </div>
<div dir="ltr" align="left"><font face="Arial"><font face="Times New Roman"><span>> </span>No,
if QGIS uses PROJ, this is just an error. </font></font></div>
<div dir="ltr" align="left"> </div>
<div><span><font face="Arial">Okay, you
may be right that QGIS does not use the file gcs.override.csv. </font></span></div>
<div><span><font face="Arial">But I see
that </font></span><span><font face="Arial">the
nad/epsg file of PROJ.4 contains </font></span><span><font face="Arial">the same erroneous </font></span></div>
<div><span><font face="Arial">+towgs84
parameters for Belge 1972 </font></span><span><font face="Arial">as the
gcs.override.csv. </font></span></div>
<div><span></span><span><font face="Arial">(At least PROJ version
4.6.1). </font></span></div>
<div><font face="Arial"><span></span></font></div>
</blockquote></div>
I have been quoting from PROJ 4.7. The older towgs parameter is not
exactly erroneous, it's just a bit les exact<div class="im"><br>
<blockquote type="cite">
<div> </div>
<div><font face="Arial"><span><font face="Times New Roman">> PROJ and EPSG use opposite rotational
formulas, and PROJ uses degrees, EPSG radians. </font></span></font></div>
<div><font face="Arial"><span></span></font> </div>
<div><font face="Arial"><span>I don't
agree in the general case. PROJ uses the Position Vector </span></font></div>
<div><font face="Arial"><span>Transform, </span></font><font face="Arial"><span>while EPSG is neutral </span></font><font face="Arial"><span>on the rotation sign
convention: </span></font></div>
<div><font face="Arial"><span>they use the
same sign convention as the original source. </span></font></div>
<div><font face="Arial"><span>And PROJ
uses arc seconds for rotations, while EPSG is neutral </span></font></div>
<div><font face="Arial"><span>on the angle
unit: </span></font><font face="Arial"><span>they
use the same angle unit as the original source</span></font></div>
<div><font face="Arial"><span>(usually arc
seconds, but sometimes </span></font><font face="Arial"><span>microradians or radians). </span></font></div>
<div><font face="Arial"><span> For the
EPSG transforms you quote, EPSG use arc-seconds</span></font></div>
<div><font face="Arial"><span>for the
rotations, </span></font><font face="Arial"><span>but either the Position Vector Transform or
the</span></font></div>
<div><font face="Arial"><span>Coordinate
Frame Rotation </span></font><font face="Arial"><span>depending on whether they got the </span></font></div>
<div><font face="Arial"><span>transform
from Eurogeographics or directly </span></font><font face="Arial"><span>from Belgium. </span></font></div>
<div><font face="Arial"><span></span></font>
<br>
</div>
</blockquote></div>
My information was for the Dutch and Belgian cases, as from the
official documents. I don't know on what principles EPSG operates, I
guess they just take it as they get it. It is not an easy-to-use
database.<br>
<br>
Jan<br>
</div>
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