[Qgis-developer] Errors in Italian new spatial ref sys?

[Juan Lucas Domínguez Rubio]

--- On Thu, 2/4/10, Niccolo Rigacci <qgis at rigacci.org> wrote:

> From: Niccolo Rigacci <qgis at rigacci.org>
> Subject: [Qgis-developer] Errors in Italian new spatial ref sys?
> To: qgis-user at lists.osgeo.org
> Cc: qgis-developer at lists.osgeo.org
> Date: Thursday, February 4, 2010, 9:43 AM
> Hello
> 
> yesterday I downloaded the srs.db from Qgis SVN, I was
> looking 
> for the new Italian srs added some days ago.
> 
> It seems to me that there are errors into the proj
> parameters:
> 
> *) For Italy Sardinia the "towgs84" is repeated twice.
> *) Somewhere there are spaces after the decimal dot and
> after the 
>    minus sign
> *) For Sicily I have a different "towgs84" formula, which
> is:
>    +towgs84=-50.2,-50.4,84.8,-0.690,-2.012,0.459,-28.08
> 
> Please can someone confirm that before I open a ticket?
> 
> 
> Here it is what I read from the srs.db:
> 
> SELECT srs_id, description, parameters, epsg FROM tbl_srs
> WHERE 
> srs_id >= 3640 AND srs_id <= 3643;
> 
> 3640|Italy mainland zone 1 GB Roma40|+proj=tmerc +lat_0=0 
> +lon_0=9 
> +k=0.9996 +x_0=1500000 +y_0=0 +ellps=intl +units=m 
> +towgs84=-104.1,-49.
> 1,-9.9,0.971,-2.917,0.714,-11.68 +no_defs|40000
> 
> 3641|Italy mainland zone 2 GB Roma40|+proj=tmerc +lat_0=0 
> +lon_0=15 +k=0.9996 +x_0=2520000 +y_0=0 +ellps=intl
> +units=m 
> +towgs84=-104.  1,-
> 49.1,-9.9,0.971,-2.917,0.714,-11.68 +no_def|40001
> 
> 3642|Italy Sardinia GB Roma40|+proj=tmerc +lat_0=0 +lon_0=9
> 
> +k=0.9996 +x_0=1500000 +y_0=0 +ellps=intl +units=m 
> +towgs84=-104.1,-49.1,- 9.9
> ,0.971,-2.917,0.714,-11.68 
> +towgs84=-168.6,-34.0,38.6,-0.374,-0.679,-1.379,-9.48 
> +no_defs|40002
> 
> 3643|Italy Sicily GB Roma40|+proj=tmerc +lat_0=0 +lon_0=9 
> +k=0.9996 +x_0=1500000 +y_0=0 +ellps=intl +units=m 
> +towgs84=-168.6,-34.0,38.6,-0
> .374,-0.679,-1.379,-9.48 +no_defs|40003
> 
> 
> -- 
> Niccolo Rigacci
> Firenze - Italy

Hello, Niccolo.

I agree. The params you propose are the ones I have sometimes used successfully for Sicily. In any case, I prefer doing empirical tests to check that the result makes sense (for example comparing with Traspunto or using some geodetic benchmark.)

Also, I think Sicily is usually considered in zone 2, like Naples, Bari, etc, no? but in those parameters, the values for lon_0 and x_0 are the ones for zone 1, I think?

Regards,
Juan Lucas