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<DIV dir=ltr align=left><SPAN class=131363214-22012010><FONT face=Arial>Jan, you
wrote </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=131363214-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=131363214-22012010>> </SPAN>All my
observations about the towgs parameters have been tested with real Belgian
coordinates overlaid over Google.</DIV>
<DIV dir=ltr align=left> </DIV>
<DIV dir=ltr align=left><SPAN class=131363214-22012010><FONT
face=Arial>Fine. But if you did make an error when transcribing the newer
transforms into Proj.4 syntax, and </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=131363214-22012010><FONT face=Arial>the
error was just in the rotation angles, then the </FONT></SPAN><SPAN
class=131363214-22012010><FONT face=Arial>effect may be too small to
notice. </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=131363214-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=131363214-22012010><FONT face=Arial>I mean,
the angles describe a rotation, so there is presumably a fixed point in Belgium
where </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=131363214-22012010><FONT face=Arial>the
rotation has no effect. If your test points happened to be near the fixed
point, the </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=131363214-22012010><FONT face=Arial>effect
of the reversed angle signs could be very small. </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=131363214-22012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=131363214-22012010><FONT face=Arial><FONT
face="Times New Roman">> As I said before, the EPSG database is not very
systematical in the way it represents its formulas, </FONT></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=131363214-22012010><FONT face=Arial><FONT
face="Times New Roman">> it just takes them from whatever source is
available, untested AFAIK. Never use them without testing them with real world
coordinates.</FONT></FONT></SPAN></DIV>
<DIV><SPAN class=131363214-22012010><FONT face=Arial><FONT
face=Arial></FONT></FONT></SPAN> </DIV>
<DIV><SPAN class=131363214-22012010><FONT face=Arial>I agree
completely. But I am not yet convinced that you are right and
EPSG wrong for the newer transforms,</FONT></SPAN></DIV>
<DIV><SPAN class=131363214-22012010><FONT face=Arial>although that is certainly
possible. Do you have some link to the offician Belgian documents?
</FONT></SPAN><SPAN class=131363214-22012010></DIV>
<DIV dir=ltr align=left><FONT face=Arial><BR></FONT></DIV></SPAN>
<DIV><SPAN class=131363214-22012010><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>www.carmenta.com</FONT> </P><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> Friday, January 22, 2010 3:27
PM<BR><B>To:</B> Mikael Rittri<BR><B>Cc:</B> PROJ.4 and general Projections
Discussions; Thibaut Gheysen<BR><B>Subject:</B> Re: [Proj] Belge 1972 / Belgian
Lambert 72 (31370) - towgs84parameters<BR></FONT><BR></DIV>
<DIV></DIV>Mikael,<BR><BR>All my observations about the towgs parameters have
been tested with real Belgian coordinates overlaid over Google. As I said
before, the EPSG database is not very systematical in the way it represents its
formulas, it just takes them from whatever source is available, untested AFAIK.
Never use them without testing them with real world
coordinates.<BR><BR>Jan<BR><BR>On 22-1-2010 13:31, Mikael Rittri wrote:
<BLOCKQUOTE cite=mid:FAF6E56B26D2044696772EBE89B1535101BDE7B6@posty.carmenta.se
type="cite">
<META name=GENERATOR content="MSHTML 8.00.6001.18854">
<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></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></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></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></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></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></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></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></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></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></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></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></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></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><A class=moz-txt-link-abbreviated
href="mailto:mikael.rittri@carmenta.com">mikael.rittri@carmenta.com</A><BR><A
class=moz-txt-link-abbreviated
href="http://www.carmenta.com">www.carmenta.com</A></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 [<A
class=moz-txt-link-freetext
href="mailto:j.l.h.hartmann@uva.nl">mailto:j.l.h.hartmann@uva.nl</A>]
<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><BR><BR>On 21-Jan-10 12:52,
Mikael Rittri wrote:
<BLOCKQUOTE
cite=mid:FAF6E56B26D2044696772EBE89B1535101BDE688@posty.carmenta.se
type="cite">
<META name=GENERATOR content="MSHTML 8.00.6001.18854">
<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></BLOCKQUOTE></BODY></HTML>