[Proj] How to convert a sphere to ellipsoid with correct datum?

[Jan Hartmann]

  Hi Cliff,

Thanks for the hints. Could you send a copy of that article? The journal 
is not available in the Netherlands.

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.

Regards,

Jan

On 09/07/10 20:13, Clifford J Mugnier wrote:
> This has been an interesting thread.  Consider taking a look at:
> G. Timár, and C.J. Mugnier, *GIS Integration of the 1:75,000 Romanian 
> Topographic Map Series from the World War I, *Geophysical Research 
> Abstracts, Vol. 11, EGU2009-1-3, 2009.
> If you look up more of Dr. Timár's publications, you will find a 
> number of helpful insights in georeferencing ancient maps of Europe.
> Cliff
> Clifford J. Mugnier, C.P., C.M.S.
> Chief of Geodesy,
> *Center for GeoInformatics*
> Department of Civil Engineering
> Patrick F. Taylor Hall 3223A
> *LOUISIANA STATE UNIVERSITY *
> Baton Rouge, LA 70803
> Voice and Facsimile: (225) 578-8536 [Academic]
> Voice and Facsimile: (225) 578-4578 [Research]
> Cell: (225) 238-8975 [Academic & Research]
> Honorary Life Member of the
> Louisiana Society of Professional Surveyors
> Fellow Emeritus of the ASPRS
> Member of the Americas Petroleum Survey Group
>
>
> ------------------------------------------------------------------------
> *From:* proj-bounces at lists.maptools.org on behalf of OvV_HN
> *Sent:* Tue 07-Sep-10 12:35
> *To:* PROJ.4 and general Projections Discussions
> *Subject:* Re: [Proj] How to convert a sphere to ellipsoid with 
> correct datum?
>
> In the mean time I've found a contemporary reference about the modified
> Flamsteed projection.
>
> Traité de topographique, d'arpentage et de nivellement, L. Puissant, 2ème
> edition, Paris, 1820.
> Chapitre III: Théorie analytique de la projection modifiée de 
> Flamsteed, pp.
> 114 f.f.
>
> It's on google books.
>
> This chapter gives a mathematical description of said projection. It's
> probably worth checking this projection against the (current 
> interpretation
> of the) Bonne projection you used.
>
> Oscar van Vlijmen
>
>
> IN REPLY TO:
>
> From: Jan Hartmann <j.l.h.hartmann <at> uva.nl>
> Subject: Re: How to convert a sphere to ellipsoid with correct datum?
> Date: 2010-09-07 10:10:24 GMT
>
> Thanks Mikkael, I'll follow that road too. I corresponded over this with a
> Dutch geodesist who programmed a datum conversion tool (Jan Hendrikse,
> http://members.home.nl/hendrikse/), but the results were not as good as
> transforming the triangulation points using the original PROJ formula, and
> afterwards rubbersheeting them to their exact modern position. There was a
> problem wit GDAL, though: it's not possible to rubbersheet an already
> georeferenced map, due to a limitation in the Geotiff format. I think now
> that it can be done by using the VRT format.
>
> And there remains the question of proof. I can (and will) compute the 
> datum
> shift, and can get a map that is within 10m accuracy, about the 
> theoretical
> maximum, but is a datum shift really the reason for the deviation? Did 
> they
> really use an ellipsoid with a different center and location in 1850? 
> I find
> it hard to believe, at least I never found an indication for that, and I
> read the handbooks used in 1850. And Cliff Mugnier doesn't think it either
> (http://lists.maptools.org/pipermail/proj/2008-November/004042.html).
>
> So, while I know now how to solve the problem computationally  and get 
> a map
> that is as exact as can be (thanks to all you input, thanks!), I am still
> wondering about the reasons for the deviation. There could be some legal
> issues (although I am not much afraid of those, it's too long ago), 
> but for
> the most I don't wont to be right for the wrong reasons. I'm not a great
> believer in statistical "proofs" where the underlying law or model is
> unknown.
>
> Thanks again for all your responses,
>
> Jan
>
>
>
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