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<DIV dir=ltr align=left><SPAN class=973163508-25012010><SPAN
class=973163508-25012010><SPAN class=084220609-25012010><FONT face=Arial>Jan,
you wrote:<BR></FONT></SPAN></SPAN></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010>> </SPAN>As I said in
a previous email:</DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT face=Arial>>
</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT
face=Arial>><SPAN class=084220609-25012010> </SPAN></FONT></SPAN><A
class=moz-txt-link-freetext
href="http://www.ngi.be/FR/FR4-4.shtm">http://www.ngi.be/FR/FR4-4.shtm</A></DIV>
<DIV dir=ltr align=left><FONT face=Arial></FONT> </DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT face=Arial>Thanks.
</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT face=Arial>This
page does not specify the rotation sign convention, as far as I could see,
</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT face=Arial>but I
downloaded the converter. Then I tried to convert the sample point 2°30'
E, <SPAN class=084220609-25012010>51</SPAN>°N </FONT></SPAN></DIV>
<DIV dir=ltr align=left><FONT face=Arial><SPAN class=973163508-25012010>(west
Belgium) from </SPAN><SPAN class=973163508-25012010>BD72 to WGS84<SPAN
class=084220609-25012010>, and compared the results with
PROJ.4.</SPAN></SPAN></FONT></DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT face=Arial>(A)
Older transform, according to Jan.<BR><SPAN
class=084220609-25012010> </SPAN>FWTools2.2.8> cs2cs
+proj=longlat +ellps=intl +towgs84=-99.059,53.322,-112.486,0.419,-0.830,1.885,-1
+to +proj=longlat +datum=WGS84<BR><SPAN
class=084220609-25012010> </SPAN>2.5 51<BR><SPAN
class=084220609-25012010>
</SPAN>2d30'4.369"E 50d59'58.092"N 41.378</FONT></SPAN></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT face=Arial>(B)
Newer transform according to Jan, assumes </FONT><A
href="http://www.ngi.be/FR/FR4-4.shtm"><FONT
face=Arial>www.ngi.be/FR/FR4-4.shtm</FONT></A><FONT face=Arial> uses Position
Vector Transform:<BR><SPAN class=084220609-25012010>
</SPAN>FWTools2.2.8> cs2cs +proj=longlat +ellps=intl
+towgs84=-106.8686,52.2978,-103.7329,-0.3366,0.457,-1.8422,-1.2747 +to
+proj=longlat +datum=WGS84<BR><SPAN class=084220609-25012010>
</SPAN>2.5 51<BR><SPAN class=084220609-25012010>
</SPAN>2d30'1.464"E 50d59'57.151"N 41.359</FONT></SPAN></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT face=Arial>(C)
Newer transform, but assuming that </FONT><A
href="http://www.ngi.be/FR/FR4-4.shtm"><FONT
face=Arial>www.ngi.be/FR/FR4-4.shtm</FONT></A><FONT face=Arial> uses Coordinate
Frame Rotation:<BR><SPAN class=084220609-25012010>
</SPAN>FWTools2.2.8> cs2cs +proj=longlat +ellps=intl
+towgs84=-106.8686,52.2978,-103.7329,0.3366,-0.457,1.8422,-1.2747 +to
+proj=longlat +datum=WGS84<BR><SPAN class=084220609-25012010>
</SPAN>2.5 51<BR><SPAN class=084220609-25012010>
</SPAN>2d30'4.373"E 50d59'58.093"N 41.455</FONT></SPAN></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT face=Arial>(D)
Result from Dutch <SPAN class=084220609-25012010>converter</SPAN>,
downloaded via </FONT><A href="http://www.ngi.be/FR/FR4-4.shtm"><FONT
face=Arial>www.ngi.be/FR/FR4-4.shtm</FONT></A><BR><FONT face=Arial><SPAN
class=084220609-25012010> </SPAN>2°30'04.37266" E,
50°59'58.09273" N </FONT></SPAN></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT face=Arial>Distance
(A) to (D):<SPAN class=084220609-25012010> </SPAN>0.08 m<BR>Distance (B)
to (D):<SPAN class=084220609-25012010> </SPAN>63.75 m <BR>Distance (C) to
(D):<SPAN class=084220609-25012010> </SPAN>0.01
m </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><SPAN
class=084220609-25012010><FONT face=Arial>(all measured by <A
href="http://williams.best.vwh.net/gccalc.htm">http://williams.best.vwh.net/gccalc.htm</A>)</FONT></SPAN></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><SPAN
class=084220609-25012010><FONT face=Arial></FONT></SPAN></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT face=Arial>I
conclude that </FONT><A href="http://www.ngi.be/FR/FR4-4.shtm"><FONT
face=Arial>www.ngi.be/FR/FR4-4.shtm</FONT></A><FONT face=Arial> uses the
Coordinate Frame Rotation, just like <BR>EPSG says in EPSG:15929, "BD72 to WGS
84(3)", and therefore, the three rotation<BR>angles should be reversed when
constructing a +towgs84 clause for PROJ.4, as in (C) above.<BR>(<SPAN
class=084220609-25012010>EPSG has in fact reversed all parameter
signs given in FR4-4, but that's because FR4-4 gives
</SPAN></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=973163508-25012010><FONT face=Arial><SPAN
class=084220609-25012010> the</SPAN></FONT></SPAN><SPAN
class=973163508-25012010><FONT face=Arial> <SPAN
class=084220609-25012010>parameters _from_ ETRS89 (or WGS84) _to_
BD72.) </SPAN><BR> <BR>Best regards,<BR></FONT></DIV></SPAN></DIV>
<DIV><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> Friday, January 22, 2010 4:04
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><BR><BR>On 22-1-2010 15:40, Mikael Rittri wrote:
<BLOCKQUOTE cite=mid:FAF6E56B26D2044696772EBE89B1535101BDE7F4@posty.carmenta.se
type="cite">
<META name=GENERATOR content="MSHTML 8.00.6001.18854">
<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></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></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></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></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></SPAN></DIV>
<DIV dir=ltr align=left><FONT face=Arial><BR></FONT></DIV></BLOCKQUOTE><BR>As I
said in a previous email:<BR><BR><A class=moz-txt-link-freetext
href="http://www.ngi.be/FR/FR4-4.shtm">http://www.ngi.be/FR/FR4-4.shtm</A><BR></BODY></HTML>