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<DIV dir=ltr><FONT color=#000000 size=2 face="Times New Roman">This has been an interesting thread. Consider taking a look at: </FONT></DIV>
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<DIV dir=ltr><FONT color=#000000 size=2 face="Times New Roman"><SPAN style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 10pt">G. Timár, and C.J. Mugnier, </SPAN><B><SPAN style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 11pt; mso-bidi-font-size: 10.0pt">GIS Integration of the 1:75,000 Romanian Topographic Map Series from the World War I, </SPAN></B><SPAN style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 11pt; mso-bidi-font-size: 10.0pt">Geophysical Research Abstracts, Vol. 11, EGU2009-1-3, 2009. </SPAN></FONT></DIV>
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<DIV dir=ltr><FONT color=#000000 size=2 face="Times New Roman"><SPAN style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 11pt; mso-bidi-font-size: 10.0pt"><FONT size=2>If you look up more of Dr. Timár's publications, you will find a number of helpful insights in georeferencing ancient maps of Europe.</FONT></SPAN></FONT></DIV>
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<DIV dir=ltr><FONT color=#000000 size=2 face="Times New Roman"><SPAN style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 11pt; mso-bidi-font-size: 10.0pt">Cliff</SPAN></FONT></DIV>
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<DIV style="MARGIN: 0in 0in 0pt" class=MsoNormal><SPAN style="FONT-SIZE: 10pt; mso-ansi-language: DE" lang=DE>Clifford J. Mugnier, C.P., C.M.S.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p></SPAN></DIV>
<DIV style="MARGIN: 0in 0in 0pt" class=MsoNormal><SPAN style="FONT-SIZE: 10pt">Chief of Geodesy,<o:p></o:p></SPAN></DIV>
<DIV style="MARGIN: 0in 0in 0pt" class=MsoNormal><B><SPAN style="FONT-VARIANT: small-caps; FONT-SIZE: 10pt">Center for GeoInformatics<o:p></o:p></SPAN></B></DIV>
<DIV style="MARGIN: 0in 0in 0pt" class=MsoNormal><SPAN style="FONT-SIZE: 10pt">Department of Civil Engineering <o:p></o:p></SPAN></DIV>
<DIV style="MARGIN: 0in 0in 0pt" class=MsoNormal><SPAN style="FONT-SIZE: 10pt">Patrick F. Taylor Hall 3223A<o:p></o:p></SPAN></DIV>
<DIV style="MARGIN: 0in 0in 0pt" class=MsoNormal><B><SPAN style="FONT-SIZE: 10pt">LOUISIANA STATE UNIVERSITY <o:p></o:p></SPAN></B></DIV>
<DIV style="MARGIN: 0in 0in 0pt" class=MsoNormal><SPAN style="FONT-SIZE: 10pt">Baton Rouge, LA<SPAN style="mso-spacerun: yes"> </SPAN>70803<o:p></o:p></SPAN></DIV>
<DIV style="MARGIN: 0in 0in 0pt" class=MsoNormal><SPAN style="FONT-SIZE: 10pt">Voice and Facsimile:<SPAN style="mso-spacerun: yes"> </SPAN>(225) 578-8536 [Academic] <o:p></o:p></SPAN></DIV>
<DIV style="MARGIN: 0in 0in 0pt" class=MsoNormal><SPAN style="FONT-SIZE: 10pt">Voice and Facsimile:<SPAN style="mso-spacerun: yes"> </SPAN>(225) 578-4578 [Research] <o:p></o:p></SPAN></DIV>
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<FONT size=2 face=Tahoma><B>From:</B> proj-bounces@lists.maptools.org on behalf of OvV_HN<BR><B>Sent:</B> Tue 07-Sep-10 12:35<BR><B>To:</B> PROJ.4 and general Projections Discussions<BR><B>Subject:</B> Re: [Proj] How to convert a sphere to ellipsoid with correct datum?<BR></FONT><BR></DIV>
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<P><FONT size=2>In the mean time I've found a contemporary reference about the modified<BR>Flamsteed projection.<BR><BR>Traité de topographique, d'arpentage et de nivellement, L. Puissant, 2ème<BR>edition, Paris, 1820.<BR>Chapitre III: Théorie analytique de la projection modifiée de Flamsteed, pp.<BR>114 f.f.<BR><BR>It's on google books.<BR><BR>This chapter gives a mathematical description of said projection. It's<BR>probably worth checking this projection against the (current interpretation<BR>of the) Bonne projection you used.<BR><BR>Oscar van Vlijmen<BR><BR><BR>IN REPLY TO:<BR><BR>From: Jan Hartmann <j.l.h.hartmann <at> uva.nl><BR>Subject: Re: How to convert a sphere to ellipsoid with correct datum?<BR>Date: 2010-09-07 10:10:24 GMT<BR><BR>Thanks Mikkael, I'll follow that road too. I corresponded over this with a<BR>Dutch geodesist who programmed a datum conversion tool (Jan Hendrikse,<BR><A href="http://members.home.nl/hendrikse/">http://members.home.nl/hendrikse/</A>), but the results were not as good as<BR>transforming the triangulation points using the original PROJ formula, and<BR>afterwards rubbersheeting them to their exact modern position. There was a<BR>problem wit GDAL, though: it's not possible to rubbersheet an already<BR>georeferenced map, due to a limitation in the Geotiff format. I think now<BR>that it can be done by using the VRT format.<BR><BR>And there remains the question of proof. I can (and will) compute the datum<BR>shift, and can get a map that is within 10m accuracy, about the theoretical<BR>maximum, but is a datum shift really the reason for the deviation? Did they<BR>really use an ellipsoid with a different center and location in 1850? I find<BR>it hard to believe, at least I never found an indication for that, and I<BR>read the handbooks used in 1850. And Cliff Mugnier doesn't think it either<BR>(<A href="http://lists.maptools.org/pipermail/proj/2008-November/004042.html">http://lists.maptools.org/pipermail/proj/2008-November/004042.html</A>).<BR><BR>So, while I know now how to solve the problem computationally and get a map<BR>that is as exact as can be (thanks to all you input, thanks!), I am still<BR>wondering about the reasons for the deviation. There could be some legal<BR>issues (although I am not much afraid of those, it's too long ago), but for<BR>the most I don't wont to be right for the wrong reasons. I'm not a great<BR>believer in statistical "proofs" where the underlying law or model is<BR>unknown.<BR><BR>Thanks again for all your responses,<BR><BR>Jan<BR><BR><BR><BR>_______________________________________________<BR>Proj mailing list<BR>Proj@lists.maptools.org<BR><A href="http://lists.maptools.org/mailman/listinfo/proj">http://lists.maptools.org/mailman/listinfo/proj</A><BR></FONT></P></DIV></BODY></HTML>