[Gvsig_english] 2D non projected coordinates conversion to EPSG 27700?

[Antonio Falciano]

Antonio Gennarini ha scritto:
> Hi,
> 
> I have a series of locations (groundwater abstractions boreholes) from a
> groundwater model in a shapefile where the locations are not
> georeferenced. They are referred to a local zero (0,0) so that Borehole
> 1 has coordinates 345.90,450.87, Borehole 2 has coordinates 443.98,
> 554.87 and so on (but the coordinates are in meters).
> 
> I'm trying to figure out how to convert the above shapefile into one
> that is georeferenced to EPSG 27700 (OSBG). The assumption is that the
> relative distance between the boreholes is maintained constant when
> moving from one system to the other. The point is that I need to
> georeference my boreholes to actual coordinates rather than to model
> (local) coordinates that have no geographic correspondence.
> Also, while I have model coordinates for all 1000 borehole, I have model
> coordinates and geographic coordinates for only 250 of the boreholes
> (maybe some of these 250 could be used as control points?).
> 
> Is there a way to georeference my model shapefile, that is currently in
> local coordinates, to a projected (EPSG 27700 which corresponds to
> Ordnance Survey GB) coordinate system? Maybe I could use the borehole
> locations that have model coordinates and OSGB? Precision and accuracy
> are not an great issue here as the groundwater model is a regional model
> where the cells are 250 m x 250 m.

Hi Antonio,
firstly, you have to convert the 250 geographic coords into projected ones.
After this, your 250 boreholes coords can be used to interpolate that
ones of the 750 remaining points using a spreadsheet. Then save all OSGB
coordinates as dbf, add it to gvSIG as a table and finally add this one
to the view as event theme.
Or more simply, you can rototranslate your model data using a whatever CAD
software, ever assuming that the transformation between the model system and
OSGB preserves relative distances.

Regards,
Antonio Falciano