[Qgis-developer] Fwd: Re: Datum Transformation - parameters for mainland Portugal

[Pedro Venâncio]

Hi Marco,


>> Since there is now a duplication, I think you can delete the grids entry 
> with coord_op_code 100004 and 100007.
> 
> With which other entries are they duplicated? Seems to me there are no two 
> entries with same source_srs / dest_src / gsb file ?
> 

coord_op_code 100004 uses the same ntv2 grid of 100014 and coord_op_code 100007 uses the same ntv2 grid of 100015.

The difference is in source_crs_code. The older ones uses 4207, that does not work for Lisbon Datum, because the code of the geographical system used by EPSG:20790 / EPSG:20791 [0] is not EPSG:4207 [1], but EPSG:4803 [2].


So, I think you can delete 100004 and 100007.


[0] http://epsg.io/20790 / http://epsg.io/20791 
[1] http://epsg.io/4207 
[2] http://epsg.io/4803 




>> No, those parameters that have +towgs84=565.04(...) are not associated with 
> any portuguese transformation. These parameters belong to epsg_nr 1571. The only 
> point of contact between this entry and the portuguese entries, is that >both 
> uses 4258 (Geographic CRS ETRS89). epsg_nr 1571 uses it as source_crs_code, and 
> some transformations for Portugal (ntv2 grids transformations) uses it as 
> target_crs_code.
> 
> 
> Not sure what you mean.
> 
> transformation epsg:1571 says there is a transformation between 4258 and 
> 4326 with +towgs84=565.04(...). So this transformation can be used for 
> all projections based on 4258 to transform to wgs84 ellipsoid (and a 
> second transformation is listed to get from wgs84 ellipsoid to the 
> destination datum).
>
 

Yes, but that transformation shows up with the following source -> destination:

4803 -> 4326;
4274 -> 4326;

witch does not make sense to me. Deleting epsg_nr 1571, the problem disappears. 

What do you think might be the cause for this behavior?


Thanks Marco!


Best regards,
Pedro