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List:       postgis-users
Subject:    Re: Proj4text is still working
From:       José_Carlos_Martínez_via_postgis-users <postgis-users () list
Date:       2024-04-26 8:58:55
Message-ID: 6e04b997-dfe9-44d6-9ad6-5763945be433 () cgf ! upv ! es
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Hi Paul

Thanks for your answer.


With a new entry in spatial_ref_sys is working but some comments:

In previous versions of PostGIS (I do not remember from which one)   I 
just used proj4text to change the 7 helmert transform values (towgs84) 
between datums.


With a new entry in spatial_ref_sys:

- Now (PostGIS 3.4), proj4text is not working, in fact I can put an 
empty text in proj4text and st_transform gives me the same results 
(after restarting the server for avoiding cache effects of proj4/postgis).

- To custom the towgs84 values, I need to change the towgs84 values in 
SRTEXT..this way its working!

It is PostGIS/Proj4 using srtext insted of proj4text? from which version?


Thanks again

Jose Martinez






El 24/04/2024 a las 16:11, Paul Ramsey escribió:
> On Wed, Apr 24, 2024 at 6:46 AM José Carlos Martínez via postgis-users
> <postgis-users@lists.osgeo.org> wrote:
> > I am making some changes in proj4text of the spatial_ref_sys table, to apply a \
> > transformation between datums (+towgs84).
> Don't make changes to existing, defined entries, make yourself a new entry.
> 
> > It appears that PostGIS is not using the values from proj4text, and instead is \
> > using the values from proj.db in the proj directory.
> Yes, if it can dereference an SRID to an entry in proj.db, that entry
> will be what is used. This allows richer and more correct transforms
> than can be achieved with the proj string entries alone.
> 
> > I would like to ask if proj4text values still take priority (as in previous \
> > versions), with respect to proj.db? I mean, the first place PostGIS looks at the \
> > values to perform a coordinate transformation is still proj4text?
> No, the first place is the proj.db. This is why if you want a custom
> system you should make a new entry.
> 
> ATB,
> 
> P
> 
> > Thanks
> > 
> > Jose Martinez
> > 
> > 
-- 
-------------------------------
José Carlos Martínez Llario
http://www.upv.es/ficha-personal/jomarlla
https://cartosig.webs.upv.es
Producción Cartográfica y SIG.
Dpto. Ingeniería Cartográfica.
Univ. Politécnica de Valencia.
-------------------------------


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