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

[Pedro Venâncio]

Hi again,



----- Mensagem original -----
> DE: Pedro Venâncio
> 
> 
>>>>  However I came across something quite odd. In the Datum 
> Transformation window, automatically arise some strange transformations (red in 
> the image http://goo.gl/iIWOuw). These transformations give huge errors, and I 
> do not understand what they represent.
> 
>>>  QGIS reads all possible combinations to get from one datum to the 
> other. Seems to me these towgs84 transformations are all present in the 
> transformation table
> 
> 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. 
> 
> 
>>>  (though I don't know . Is it 4258?) 
> 
> The biggest mess in my mind is precisely this. Is that, even the possible 
> incorrect match between source and target codes does not make sense, because the 
> geographical crs related to 30004 is 4326 (+towgs84). We only use 4258 for ntv2 
> grids.
> 
> So, these options in red in the image should not show up. I think this problem 
> only happens with the portuguese transformations, right Giovanni?
> 
> 


I can now confirm that it is a conflict with epsg_nr 1571, because deleting this record

delete from tbl_datum_transform
where epsg_nr = 1571;


the problem disappears.


Best regards,
Pedro