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

[Benjamin Ducke]

I thing adding support for .wld files for CAD formats
makes sense, but not for any GIS vector data formats.
A GIS data file like ESRI Shapefile already contains
geometries with geographic coordinates. Most users also
will not associate the .wld file with shapefiles.
So a stale .wld file left in the file system (e.g. because
a delete operation did not take care of removing it), can
have the most confusing effects for the user.

I can see several solutions:

1. Add the ability to compute affine transformations from
.wld files to SEXTANTE's Transform.

2. Add the ability to read the simple point format in a
.wld file to the "Transform" process of the Topology
Extension (available via the Geoprocessing toolbox).

3. Ask user to compute and apply transformation if a CAD
file is added to a view and a .wld file exists.

Ben

----- Original Message -----
> 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
> sede istituzionale: piazza Aldo Moro, 1 - 92100 AGRIGENTO
> sede operativa: via Acrone, 27 - 92100 AGRIGENTO
> cell. 3392718463 (personale)
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> tel. uff 0922593752
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