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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><FONT
face=Arial></FONT></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><FONT face=Arial><FONT
face="Times New Roman"></FONT></FONT> </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><FONT
face=Arial></FONT></SPAN></FONT> </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><FONT
face=Arial></FONT></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> </DIV>
<DIV><FONT face=Arial><SPAN class=176502811-21012010><FONT
face="Times New Roman"><FONT face=Arial></FONT></FONT></SPAN>R<SPAN
class=176502811-21012010>egards,</SPAN></FONT></DIV>
<DIV><FONT face=Arial><SPAN class=176502811-21012010></SPAN><BR></FONT><FONT
size=2>--<BR>Mikael Rittri<BR>Carmenta AB<BR>SWEDEN<BR>www.carmenta.com</FONT>
<BR></DIV>
<DIV dir=ltr lang=en-us class=OutlookMessageHeader align=left>
<HR tabIndex=-1>
<FONT size=2 face=Tahoma><B>From:</B> Jan Hartmann
[mailto:j.l.h.hartmann@uva.nl] <BR><B>Sent:</B> Wednesday, January 20, 2010 3:23
PM<BR><B>To:</B> PROJ.4 and general Projections Discussions<BR><B>Cc:</B> Mikael
Rittri<BR><B>Subject:</B> Re: [Proj] Belge 1972 / Belgian Lambert 72 (31370) -
towgs84parameters<BR></FONT><BR></DIV>
<DIV></DIV>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">
<META name=GENERATOR content="MSHTML 8.00.6001.18854">
<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
href="http://svn.osgeo.org/metacrs/geotiff/trunk/libgeotiff/csv/gcs.override.csv"
moz-do-not-send="true">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 lang=en-us class=OutlookMessageHeader align=left>
<HR tabIndex=-1>
<FONT size=2 face=Tahoma><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 class=moz-txt-link-abbreviated
href="http://www.epsg.org" moz-do-not-send="true">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 class=moz-txt-link-freetext
href="http://www.ngi.be/FR/FR4-4.shtm"
moz-do-not-send="true">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><PRE wrap=""><FIELDSET class=mimeAttachmentHeader></FIELDSET>
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