What proj releases are you using? `Select postgis_full_version()` will show it.
It is likely that your 3.0 is using PROJ6+ which has more precise transformations. On Thu, Apr 23, 2020 at 2:55 PM David McKelvie <[email protected]> wrote: > > > Hello; > > Ive noticed a difference between the results returned by st_transform > between Postgis 2.3 and Postgis 3.0 and wonder if anyone on this list > might be able to explain why that is so. > > I have a home rolled entry in the spatial_ref_sys table for a SRID called > 927700. This is the UK Ordnance Survey coordinate system using OSTN02. > > The spatial_ref_sys.proj4text for this is > (newline added for readability) > > '+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 > +y_0=-100000 +ellps=airy +units=m +no_defs +nadgrids=OSTN02_NTv2.gsb' > > So it is using a gsb data file. > > The following query shows a difference > converting a point in 4326 'WGS 84' to 927700 "OSGB 1936 / British National > Grid" > > SELECT st_asewkt(st_transform(geomfromEWKT( > 'SRID=4326;POINT(-0.077731 54.116851 86.778)' > ), 927700)) AS a; > > postgres / postgis result > 9.6 / 2.3 SRID=927700;POINT(525745.680454343 470703.162768111 86.778) > 9.6 / 3.0 SRID=927700;POINT(525744.779056573 470705.423178893 86.778) > > A difference of -0.901 2.26 which is quite significant given that OSGB > is measured in meters. > > Any ideas what is going on? > > David McKelvie > > _______________________________________________ > postgis-users mailing list > [email protected] > https://lists.osgeo.org/mailman/listinfo/postgis-users -- Raúl Marín Rodríguez carto.com _______________________________________________ postgis-users mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/postgis-users
