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

[Andre Joost]

Am 20.06.2014 13:41, schrieb Marco Hugentobler:

>> 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.
>>

tfm 1571 is a bug in the EPSG database. It should be "Amersfoort to 
ETRS89 (1)", but somehow the source CRS got wrong.

It was deprecated in 2001, and replaced by tfm 1751 (4289 to 4258) under 
the same name.
For some reasons, EPSG still keeps it in its database, marked 
"deprecated". The online version of the database does not show it 
anymore, so I think QGIS can drop transformations marked deprecated as well.

Usually, ETRS89 and WGS84 are concidered identical. There is another tfm 
1149 from 4258 to 4326 with all parameters to zero.

The transformation table inside QGIS only has those tfm from the EPSG 
database where the target CRS is 4326 (we want towgs84, right?)

So I suggest to set target CRS for all new portuguese CRS to 4326 as well.

For the other bug about Lisbon datum with prime meridian Greenwich vs 
Lisbon, I have to investigate a bit further. Maybe the low accuracy tfm 
now used applies to both within the range of accurancy.

@pedro: I really would encourage you to get this into the EPSG database 
as soon as possible.

Greetings,
André Joost