[Gvsig_english] Raster georeferencing

[G. Allegri]

Scrivo in privato perché un po' OT, ma visto che ha nominato altri sw
Open Source (ILWIS) le volevo indicare, se già non lo sapesse, che
anche Grass permette di eseguire trasformazioni polinomiali anche di
secondo e terzo ordine. Il ricampionamento dell'immagine è molto
efficiente, soprattutto perché viene eseguito internamente al formato
ottimizzato di Grass. Fatta la riproiezione il raster può, ovviamente,
essere riesportato in diversi formati.

Giovanni

2008/1/29, ernesto sferlazza <e.sferlazza at gmail.com>:
> Hi all (Developers & Users)
> If I have correctly understood, when I georeference a raster image using
> GVSIG, the program accepts in input a set of point given in two coordinate
> system (e.g. file coordinates, in pixel and map coordinates, in meters) and
> performs a affine transformation (resolved in change of scale in X, change
> of scale in Y, skew of X axis, skew of Y axis, shift of X coord. of origin
> and shift of Y coord of origin). Then, the parameters of the above mentioned
> transformation are written in the world file (e.g. the "tfw" file associated
> to a tiff, or the "jgw" file associated to a jpg image). At the same time,
> the same information added to other regarding the projection and the image
> size (both in pixel and in meters) are stored in another file contaning xml
> code (with extention "tmp").
> I have two remarks to the point:
> 1) the "skew" parameters (rotation of X and Y axes) written in the world
> file are ignored (are considered equal to "0") by some GIS sw (e.g. ESRI
> ArcView 3.x) and there is a lack of "interoperability";
> 2) it would be appreciated very much the possibility to use polinomial
> transformation of higher order (2nd, 3rd) than the affine (1st order), or,
> even more, projective transformation (using the homology theory), or rubber
> sheeting, to perform different kinds of transformations. In this cases,
> obviously, the transformation informations cannot be stored in the world
> file and arises the need of create a new raster, by performing a resampling
> based on the transformed original raster. In this way the axes of the new
> raster file will be parallel to the map axes and the world file will not
> contain rotation axes parameters.
>
> I found that ILWIS (Open Source) performs many transformation, but the
> change of raster format consumes too much time.
> Best regards
> --
> ing. Ernesto Sferlazza
> responsabile nodo provinciale di Agrigento del SITR Sicilia
> resp. U.O. Sistema Informativo Territoriale
> Provincia regionale di Agrigento
> sede istituzionale: piazza Aldo Moro, 1 - 92100 AGRIGENTO
>  sede operativa: via Acrone, 27 - 92100 AGRIGENTO
> cell. 3392718463
> tel. uff 0922401935
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