[Gvsig_english] WMS and WCS raster pixel dimensions

[fla83tn at libero.it]

Hi to all,
I want to use sextante extension of gvSIG in order to compute z-
dimension of 2-dimensional shapes using a DEM (Digital Elevatoin Model) layer.

The DEM layer is a raster file, which has the following raster attributes if 
loaded from file system:

X pixel Dimension: 2.5
Y pixel Dimension: -2.5
X 
rotation: 0.0
Y rotation: 0.0

If I load the same layer via WMS or WCS instead 
(which is a GeoTiff image on the UMN Mapserver), the X pixel Dimension and Y 
pixel Dimension 
vary with respect to the width/height of the image in the 
Vista form.
This causes problem when calculating the z-dimension of my 2-
dimensional shapes.

How could I fix the X pixel Dimension and Y pixel 
Dimension of the raster?

Any help is appreciated,
Flavio