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<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>Jan
Hartmann wrote:</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>>
</FONT><FONT face="Times New Roman">I have been quoting from PROJ 4.7. The older
towgs parameter is not exactly erroneous, it's just a bit less
exact.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>But
Thibaut's image showed an displacement of about 190 meters. I call that
erroneous.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>Well, if
by "older", you mean the EPSG datum shifts </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial> 1652 "BD72 to ETRS89 (1)"
and 1609 "BD72 to WGS 84 (1)"</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>you are
right that they are just a bit less exact than EPSG datum shifts
</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial> 15928 "BD72 to ETRS89 (1)"
</FONT></SPAN><SPAN class=553020612-22012010><FONT face=Arial>and 15929 "BD72 to
WGS 84 (3)"</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>But the
towgs84 found in the current gcs.override.csv, as well as in PROJ's nad/epsg
file </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>(at
least in 4.6.1), are just wrong. I think the wrong sign for DX, DY and DZ
causes most </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>of the
190 meter error. </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>By the
way, in your first letter, you gave the older transforms as </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><SPAN
class=553020612-22012010>>
+towgs84=-99.059,53.322,-112.486,0.419,-0.830,1.885,-1</SPAN></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><SPAN
class=553020612-22012010></SPAN></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><SPAN
class=553020612-22012010><FONT face=Arial>which I think is correct, but you gave
the newer transforms as </FONT></SPAN></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>>
</FONT><FONT
face="Times New Roman">+towgs84=-106.8686,52.2978,-103.7329,-0.3366,0.457,-1.8422,-1.2747
</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>which I
think has the wrong sign for the rotation angles: it should be
</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT face=Arial>>
</FONT><FONT
face="Times New Roman">+towgs84=-106.8686,52.2978,-103.7329,0.3366,-0.457,1.8422,-1.2747
</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face="Times New Roman"></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face="Times New Roman">instead. (I base this correction on the fact that
EPSG claims that their datum shifts 15928 and 15929</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face="Times New Roman">use the Coordinate Frame Rotation, so the rotation signs
have to be reversed for PROJ.4. If the </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face="Times New Roman">claim of EPSG contradicts the official documents - it
happens now and then - please notify EPSG.)
</FONT></SPAN></DIV></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=553020612-22012010><FONT
face=Arial>Regards,</FONT></SPAN></DIV><!-- Converted from text/plain format -->
<P><FONT size=2>--<BR>Mikael Rittri<BR>Carmenta AB<BR>Box 11354<BR>SE-404 28
Göteborg<BR>Visitors: Sankt Eriksgatan 5<BR>SWEDEN<BR>Tel: +46-31-775 57
37<BR>Mob: +46-703-60 34
07<BR>mikael.rittri@carmenta.com<BR>www.carmenta.com</FONT> </P>
<DIV> </DIV><BR>
<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> Thursday, January 21, 2010 11:51
PM<BR><B>To:</B> Mikael Rittri<BR><B>Cc:</B> PROJ.4 and general Projections
Discussions<BR><B>Subject:</B> Re: [Proj] Belge 1972 / Belgian Lambert 72
(31370) - towgs84parameters<BR></FONT><BR></DIV>
<DIV></DIV><BR><BR>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></BODY></HTML>