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<font face="Times New Roman">Hi Cliff,<br>
<br>
Thanks for the hints. Could you send a copy of that article? The
journal is not available in the Netherlands.<br>
<br>
And would appreciate if you could give me a few of Dr. Timar's
titles. The search interface of our National Library shows
thousands of hits on that name, mostly in Hungarian by people
called Attilla.<br>
</font><br>
Regards,<br>
<br>
Jan<br>
<br>
On 09/07/10 20:13, Clifford J Mugnier wrote:
<blockquote
cite="mid:B597ADFC46B67741B18EA6AA13613FF7026A649D@email002.lsu.edu"
type="cite">
<title>Re: [Proj] How to convert a sphere to ellipsoid with
correct datum?</title>
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<div dir="ltr" id="idOWAReplyText65628">
<div dir="ltr"><font color="#000000" face="Times New Roman"
size="2">This has been an interesting thread. Consider
taking a look at: </font></div>
<div dir="ltr"> </div>
<div dir="ltr"><font color="#000000" face="Times New Roman"
size="2"><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;">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;">Geophysical Research
Abstracts, Vol. 11, EGU2009-1-3, 2009. </span></font></div>
<div dir="ltr"><font color="#000000" face="Times New Roman"
size="2"><span style="font-family: 'Times New
Roman','serif'; font-size: 11pt;"></span></font> </div>
<div dir="ltr"><font color="#000000" face="Times New Roman"
size="2"><span style="font-family: 'Times New
Roman','serif'; font-size: 11pt;"><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>
<div dir="ltr"><font color="#000000" face="Times New Roman"
size="2"><span style="font-family: 'Times New
Roman','serif'; font-size: 11pt;"></span></font> </div>
<div dir="ltr"><font color="#000000" face="Times New Roman"
size="2"><span style="font-family: 'Times New
Roman','serif'; font-size: 11pt;">Cliff</span></font></div>
<div dir="ltr"> </div>
</div>
<div dir="ltr" id="idSignature13097">
<div><font color="#000000" face="Times New Roman" size="2"><span
style="font-size: 10pt;">
<div style="margin: 0in 0in 0pt;" class="MsoNormal"><span
style="font-size: 10pt;" lang="DE">Clifford J.
Mugnier, C.P., C.M.S.<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="">
</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=""> </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=""> </span>(225) 578-4578 [Research] <o:p></o:p></span></div>
<div style="margin: 0in 0in 0pt;" class="MsoNormal"><span
style="font-size: 10pt;">Cell: (225) 238-8975
[Academic & Research]<o:p></o:p></span></div>
<div style="margin: 0in 0in 0pt;" class="MsoNormal"><span
style="font-size: 10pt;">Honorary Life Member of the <o:p></o:p></span></div>
<div style="margin: 0in 0in 0pt;" class="MsoNormal"><span
style="font-size: 10pt;">Louisiana Society of
Professional Surveyors <o:p></o:p></span></div>
<div style="margin: 0in 0in 0pt;" class="MsoNormal"><span
style="font-size: 10pt;">Fellow Emeritus of the ASPRS
<o:p></o:p></span></div>
<div style="margin: 0in 0in 0pt;" class="MsoNormal"><span
style="font-size: 10pt;">Member of the Americas
Petroleum Survey Group<o:p></o:p></span></div>
<br>
</span></font></div>
</div>
<div dir="ltr"><br>
<hr tabindex="-1">
<font face="Tahoma" size="2"><b>From:</b>
<a class="moz-txt-link-abbreviated" href="mailto:proj-bounces@lists.maptools.org">proj-bounces@lists.maptools.org</a> 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>
<div>
<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 moz-do-not-send="true"
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 moz-do-not-send="true"
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>
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