Hi Pedro
QGIS imports the towgs84 transformations from GDAL and adds a list of
ntv2 transformations into srs.db.
So I'm going to add/modify the ntv2 transformations (if there are no
objections from other portuguese users). For the towgs84 ones I agree
with Andre that it is better to bring it to gdal/epsg level.
Regards,
Marco
On 18.06.2014 16:59, Andre Joost wrote:
Hi Pedro,
Am 18.06.2014 15:13, schrieb Pedro Venâncio:
I have an update to the parameters that are in Datum Transformation
for mainland Portugal.
After an analysis of the parameters that are currently inserted in
srs.db, I think we should keep only the latest parameters that are
provided by the Portuguese Surveying Authority (Directorate-General
of the Territory), to avoid confusion among users.
So, we should keep only the transformation parameters of Molodensky,
Bursa-Wolf, and two grids NTv2 that are in use here in Portugal, one
from the Directorate-General of the Territory, and another from the
University of Porto.
it has little use to change the parameters in QGIS only.
All applications that use GDAL/PROJ use the same database of CRS. This
is kept in sync with the official EPSG database at
<http://www.epsg-registry.org/>
The EPSG database offers different transformations from local datums
to WGS84. One of these is usually bundled to the coordinate system
when you use QGIS/GDAL/PROJ. Other software like ARCGIS keeps
coordinate systems and datum transformations separated.
Latest versions of QGIS allow to use a different datum transformation,
but keep in mind that software that stores only EPSG codes (like
spatialite) will use nethertheless the default datum transformation.
If you feel uncomfortable with the default datum transformation, and
you have "official" sources, you might open a ticket for the CRS
databases used in GDAL and PROJ. The parameters should be at least in
the EPSG database.
QGIS syncs with that database after installation to avoid
discrepancies on your own computer.
Greetings,
André Joost
_______________________________________________
Qgis-developer mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/qgis-developer
--
Dr. Marco Hugentobler
Sourcepole - Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
[email protected] http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee
_______________________________________________
Qgis-developer mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/qgis-developer
