Am 31.03.2016 um 16:55 schrieb Nicolas Cadieux:
Hi Andreas, That is very interesting. I would like to know more about these grids and how QGIS deals with it. Do you have any additional links to share? All I can see is that the proj4 parameters for many of the CRS in North America are identical and lead to no actual changes in the coordinate unless you are going from nad27 to nad 83 or Wgs84 which is more drastic. That is why I use the nrcan tool that can do transformation based on ITRF and WGS84 CRS. I would be nice to do that strait in QGIS. I will look into your method and report back.
QGIS already uses a grid shift file internally for the conversion from NAD27 to WGS84. But there is not yet any grid shift file that reflects newer tectonic moves, like NAD83(CSRS98) would need.
If you have one, you need to build a custom CRS with a link to the file. A sample entry would be:
+proj=tmerc +lat_0=39.66666666666666 +lon_0=-8.131906111111112 +k=1 +x_0=0 +y_0=0 +ellps=intl +nadgrids=./DLX_ETRS89_geo.gsb +units=m +no_defs
It might help to set the complete path to the .gsb file. Greetings, André Joost _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: http://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user
