[gdal-dev] pre-rectifying to georeference old maps

Carlo A. Bertelli (Charta s.r.l.) bertelli at charta.acme.com
Fri Nov 13 05:23:46 EST 2009

dealing with old maps which have to be georeferenced we are not able
to solve a problem: sometimes old (very old, 18th or even 17th century
maps) cannot be scanned flat or may only be photographed. This leads
to bending, shading and so on. The margins of the map become curved
and the light uneven, not to talk about maps which were conservated in
albums: the center fold is deeply shaded and aroud it the curved paper
Researchers developed image recognition techniques to solve this
problems for book reproductions (I have refereces, if someone is
interested) but those need to have informations on light directions
and so on (they use shade to detect shape); this technique is mainly
useful for scanned images.
In the old times, I remember using Bentley's IRAS/C to solve a simpler
issue (a curved map), by now I think gdalwarp would possibly solve
deformation problems -- but how to set data to make it run properly in
this case, I cannot imagine how to use it without a GUI to set points,
maybe a vector polygon to set the deformation. An this would only be
good for shape, not for shade (surely useful but not perfect).
Any suggestion is gratefully accepted.

Carlo A. Bertelli
   Charta servizi e sistemi per il territorio e la storia ambientale srl
          Dipendenze del palazzo Doria,
          vc. alla Chiesa della Maddalena 9/2 16124      Genova (Italy)
          tel. +39(0)10 2475439  fax +39(0)10 2475439  gsm:+39 393 1590711
   e-mail: bertelli at charta.acme.com      http://www.charta.acme.com

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