[Gvsig_english] world file and on-the fly transformation for vector layers

[ernesto sferlazza]

Hello gvSIG developers.
I reply a very old issue (15-01-2007), that I wrote to gvSIG team
ahead of my subcrition to the international list.
>
> " it would be very useful to implement "on the fly transformation" of CAD layers, using "wld" files. In this way it is possible , for example, to use a CAD cartography georeferenced in local coordinates in a view frame referenced in UTM-WGS84, without the need of create a new CAD file moving all the features from the first to the second cartographic system.
> [...]
> The "wld" file is simply a text file containing the informations that allow the software to calculate the parameters of a particular affine transformation (i know it is called "similitude") composed of a rigid rotation, a shift of the origin of axis  and an uniform change of overall scale. The called informations consist of the coordinates of two points, given in two different frames of reference: the start frame and the target frame [...] .
> From the informations contained in the "wld" file it is possible, using a worksheet and a CAD software [...], to perform quickly the transformation, calculating the parameters of rotation, overall scale and shifting and applying them to the CAD drawing, using the command line"


Nowadays the only way I have found to perform such transformation with
gvSIG + Sextante consists of the following steps:
1) export the CAD file to the SHP format;
2) given the coordinates of two points,  both in in the start frame
end in the target frame, I can calculate the parameters of
translation, rotation, scale factor and anchor point coordinates
needed to perform a similitude transformation (I can use the
following spreadsheet:
http://www.provincia.agrigento.it/flex/cm/pages/ServeAttachment.php/L/IT/D/D.c460f62201e21373447d/P/BLOB%3AID%3D309

3)  use the "transform" algorithm of Sextante, using the above
mentioned parameters as input.

This procedure works fine, but is quite farraginous compared to the
simplest use of "wld" file performed by ArcGIS.
Implementing this feature, even spread to all vector formats, shp
included,  would be a great improvement for interoperability too.
Best regards.
Ernesto


--
ing. Ernesto Sferlazza
responsabile nodo provinciale di Agrigento del SITR Sicilia
resp. gruppo Sistema Informativo Territoriale
Provincia regionale di Agrigento
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