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
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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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