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On 21-Jan-10 12:52, Mikael Rittri wrote:
<blockquote
cite="mid:FAF6E56B26D2044696772EBE89B1535101BDE688@posty.carmenta.se"
type="cite">
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<div dir="ltr" align="left"><span class="176502811-21012010"><font
face="Arial">Jan Hartmann wrote: </font></span></div>
<div dir="ltr" align="left"><span class="176502811-21012010"></span> </div>
<div dir="ltr" align="left"><font face="Arial"><font
face="Times New Roman"><span class="176502811-21012010">> </span>No,
if QGIS uses PROJ, this is just an error. </font></font></div>
<div dir="ltr" align="left"> </div>
<div><span class="176502811-21012010"><font face="Arial">Okay, you
may be right that QGIS does not use the file gcs.override.csv. </font></span></div>
<div><span class="176502811-21012010"><font face="Arial">But I see
that </font></span><span class="176502811-21012010"><font face="Arial">the
nad/epsg file of PROJ.4 contains </font></span><span
class="176502811-21012010"><font face="Arial">the same erroneous </font></span></div>
<div><span class="176502811-21012010"><font face="Arial">+towgs84
parameters for Belge 1972 </font></span><span
class="176502811-21012010"><font face="Arial">as the
gcs.override.csv. </font></span></div>
<div><span class="176502811-21012010"></span><span
class="176502811-21012010"><font face="Arial">(At least PROJ version
4.6.1). </font></span></div>
<div><font face="Arial"><span class="176502811-21012010"></span></font></div>
</blockquote>
I have been quoting from PROJ 4.7. The older towgs parameter is not
exactly erroneous, it's just a bit les exact<br>
<blockquote
cite="mid:FAF6E56B26D2044696772EBE89B1535101BDE688@posty.carmenta.se"
type="cite">
<div> </div>
<div><font face="Arial"><span class="176502811-21012010"><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 class="176502811-21012010"></span></font> </div>
<div><font face="Arial"><span class="176502811-21012010">I don't
agree in the general case. PROJ uses the Position Vector </span></font></div>
<div><font face="Arial"><span class="176502811-21012010">Transform, </span></font><font
face="Arial"><span class="176502811-21012010">while EPSG is neutral </span></font><font
face="Arial"><span class="176502811-21012010">on the rotation sign
convention: </span></font></div>
<div><font face="Arial"><span class="176502811-21012010">they use the
same sign convention as the original source. </span></font></div>
<div><font face="Arial"><span class="176502811-21012010">And PROJ
uses arc seconds for rotations, while EPSG is neutral </span></font></div>
<div><font face="Arial"><span class="176502811-21012010">on the angle
unit: </span></font><font face="Arial"><span class="176502811-21012010">they
use the same angle unit as the original source</span></font></div>
<div><font face="Arial"><span class="176502811-21012010">(usually arc
seconds, but sometimes </span></font><font face="Arial"><span
class="176502811-21012010">microradians or radians). </span></font></div>
<div><font face="Arial"><span class="176502811-21012010"> For the
EPSG transforms you quote, EPSG use arc-seconds</span></font></div>
<div><font face="Arial"><span class="176502811-21012010">for the
rotations, </span></font><font face="Arial"><span
class="176502811-21012010">but either the Position Vector Transform or
the</span></font></div>
<div><font face="Arial"><span class="176502811-21012010">Coordinate
Frame Rotation </span></font><font face="Arial"><span
class="176502811-21012010">depending on whether they got the </span></font></div>
<div><font face="Arial"><span class="176502811-21012010">transform
from Eurogeographics or directly </span></font><font face="Arial"><span
class="176502811-21012010">from Belgium. </span></font></div>
<div><font face="Arial"><span class="176502811-21012010"></span></font>
<br>
</div>
</blockquote>
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>
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