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No, if QGIS uses PROJ, this is just an error. PROJ and EPSG use
opposite rotational formulas, and PROJ uses degrees, EPSG radians.
Could you report this bug to the the QGIS team?<br>
<br>
Jan <br>
<br>
On 20-1-2010 14:04, Mikael Rittri wrote:
<blockquote
cite="mid:FAF6E56B26D2044696772EBE89B1535101BDE5A4@posty.carmenta.se"
type="cite">
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<div dir="ltr" align="left"><span class="676244412-20012010"><font
face="Arial">Hello Thibaut and Jan,</font></span></div>
<div dir="ltr" align="left"><span class="676244412-20012010"><font
face="Arial">The towgs84 parameters you say that QGIS is using, seems
to come from the file </font></span></div>
<div dir="ltr" align="left"><span class="676244412-20012010"></span> </div>
<div dir="ltr" align="left"><span class="676244412-20012010"><font
face="Arial"> <a moz-do-not-send="true"
href="http://svn.osgeo.org/metacrs/geotiff/trunk/libgeotiff/csv/gcs.override.csv">http://svn.osgeo.org/metacrs/geotiff/trunk/libgeotiff/csv/gcs.override.csv</a></font></span></div>
<div dir="ltr" align="left"><span class="676244412-20012010"></span> </div>
<div dir="ltr" align="left"><span class="676244412-20012010"><font
face="Arial">that is used by libgeotiff and GDAL. The datum shifts in
this file have been </font></span></div>
<div dir="ltr" align="left"><span class="676244412-20012010"><font
face="Arial">constructed manually. For Belge 72 they seem to be
wrong, </font></span><span class="676244412-20012010"><font
face="Arial">as you noted:</font></span></div>
<div dir="ltr" align="left"><span class="676244412-20012010"></span> </div>
<div dir="ltr" align="left"><span class="676244412-20012010"><font
face="Arial"> The signs of DX, DY and DZ are wrong,</font></span></div>
<div dir="ltr" align="left"><span class="676244412-20012010"><font
face="Arial"> The signs of RX, RY and RZ are correct, provided
that the COORD_OP_METHOD_CODE is changed to 9607,</font></span></div>
<div dir="ltr" align="left"><span class="676244412-20012010"><font
face="Arial"> The DS is 1.0000012747, but should be -1.2747
(expressed in unity instead of parts per million, and wrong sign). </font></span></div>
<div dir="ltr" align="left"><span class="676244412-20012010"></span> </div>
<div dir="ltr" align="left"><span class="676244412-20012010"><font
face="Arial">(This is assuming that the datum shift EPSG:15928 is
correct.)</font></span></div>
<div dir="ltr" align="left"><span class="676244412-20012010"></span> </div>
<div dir="ltr" align="left"><span class="676244412-20012010"><font
face="Arial">I think the parameters in gcs.override.csv came from an
information source</font></span></div>
<div dir="ltr" align="left"><span class="676244412-20012010"><font
face="Arial">that gave </font></span><span class="676244412-20012010"><font
face="Arial">the datum shift in the direction <em>from</em> WGS84 <em>to</em>
Belge 72. </font></span></div>
<div dir="ltr" align="left"><span class="676244412-20012010"></span> </div>
<div dir="ltr" align="left"><span class="676244412-20012010"><font
face="Arial">Best regards,</font></span></div>
<!-- Converted from text/plain format -->
<p><font size="2">--<br>
Mikael Rittri<br>
Carmenta AB<br>
SWEDEN<br>
<a class="moz-txt-link-abbreviated" href="http://www.carmenta.com">www.carmenta.com</a></font> </p>
<div dir="ltr" class="OutlookMessageHeader" align="left" lang="en-us">
<hr tabindex="-1"><font face="Tahoma" size="2"><b>From:</b>
<a class="moz-txt-link-abbreviated" href="mailto:proj-bounces@lists.maptools.org">proj-bounces@lists.maptools.org</a>
[<a class="moz-txt-link-freetext" href="mailto:proj-bounces@lists.maptools.org">mailto:proj-bounces@lists.maptools.org</a>] <b>On Behalf Of </b>Jan
Hartmann<br>
<b>Sent:</b> Wednesday, January 20, 2010 11:29 AM<br>
<b>To:</b> PROJ.4 and general Projections Discussions<br>
<b>Subject:</b> Re: [Proj] Belge 1972 / Belgian Lambert 72 (31370) -
towgs84parameters<br>
</font><br>
</div>
Hi Thibaut,<br>
<br>
the most recent version of the EPSG database, 7.4, (<a
moz-do-not-send="true" class="moz-txt-link-abbreviated"
href="http://www.epsg.org">www.epsg.org</a>) has two definitions for
the datum shift from Belge Lambert to WGS84 (they call it a coordinate
transformation). I'l give the parameters as a PROJ string, with
rotations converted from radians to degrees and sign-converted<br>
<br>
nr 162 and 164 (accurate to a meter) : +proj=lcc
+lat_1=51.16666723333333 +lat_2=49.8333339 +lat_0=90
+lon_0=4.367486666666666 +x_0=150000.013 +y_0=5400088.438 +ellps=intl
+towgs84=-99.059,53.322,-112.486,0.419,-0.830,1.885,-1 +units=m +no_defs<br>
<br>
nr 163 and 166: (accurate to 20 cm): +proj=lcc +lat_1=51.16666723333333
+lat_2=49.8333339 +lat_0=90 +lon_0=4.367486666666666 +x_0=150000.013
+y_0=5400088.438 +ellps=intl
+towgs84=-106.8686,52.2978,-103.7329,-0.3366,0.457,-1.8422,-1.2747
+units=m +no_defs <br>
<br>
The second one if the official one from the Belgian National Geographic
Institute (<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://www.ngi.be/FR/FR4-4.shtm">http://www.ngi.be/FR/FR4-4.shtm</a>).
Both should give approximately the same results. I have used
epsg:31370, which uses the second definition without errors. The errors
in your picture, about 100 meters, look as if no datum transformation
has been applied at all.<br>
<br>
You could test this by transforming your data points manually with
cs2cs for both towgs84 strings, and compare the results with the
position of the WGS84 coordinates in QGIS <br>
<br>
Jan<br>
<br>
On 20-1-2010 10:18, Thibaut Gheysen wrote:
<blockquote
cite="mid:94e91cde1001200118x16b58727x21ce687c3598e4d3@mail.gmail.com"
type="cite">Hi,<br>
<br>
I have a problem in QGIS 1.4.0 when I reproject a gpx file into Belgian
lambert 72 coordinate system : the waypoints are not correctly placed
on the map (see this image : <a
href="http://www.fsagx.ac.be/gf/outilslogiciels/Garbel/proj4.jpg"
moz-do-not-send="true">http://www.fsagx.ac.be/gf/outilslogiciels/Garbel/proj4.jpg</a>).
I already have a similar problem when writing a GPS software (<a
href="http://lists.maptools.org/pipermail/proj/2006-August/002447.html"
moz-do-not-send="true">http://lists.maptools.org/pipermail/proj/2006-August/002447.html</a>).
To solve this I have used this towgs84 parameters :
+towgs84=-99.059,53.322,-112.486,0.419,-0.83,1.885,-0.999999. In QGIS,
the towgs84 parameters are different
(+towgs84=106.869,-52.2978,103.724,-0.33657,0.456955,-1.84218,1). When
I use my GPS software to reproject into Belgian Lambert 72 the
waypoints are correctly placed (red points in the image) but not when I
use QGIS (yellow points). I think thus there is a problem in the epsg
31370 definition.<br>
<br>
Best regards,<br>
Thibaut.<br>
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