Thank you, Jeff. This is helpful. Shira
On Thu, Jul 23, 2020 at 5:04 AM Jeff McKenna <[email protected]> wrote: > For the history of this: I first reported this shift back in 2018 > (http://lists.maptools.org/pipermail/proj/2018-February/008082.html). > It was fixed for 3857 in the PROJ 5.2.0 release. > > My advice to you is to change to using EPSG:3857 as most software now no > longer supports the non-standard "900913". > > -jeff > > > > -- > Jeff McKenna > MapServer Consulting and Training Services > co-founder of FOSS4G > http://gatewaygeo.com/ > > > > > > On 2020-07-20 3:25 p.m., Shira Bezalel wrote: > > We recently recompiled PostGIS in one of our Postgres 12.3 environments > > with PROJ 6 (6.3.2) from PROJ 4 (4.9.3). > > > > postgis_full_version() output: > > POSTGIS="3.0.1 ec2a9aa" [EXTENSION] PGSQL="120" GEOS="3.7.1-CAPI-1.11.1 > > 27a5e771" PROJ="6.3.2" LIBXML="2.9.4" LIBJSON="0.12.1" > > > > We're now noticing that using ST_Transform(geometry, srid)**to transform > > some points in California from SRID 4326 to 900913 is causing a shift > > along the Y axis of about 20-30 meters. The difference is evidenced by a > > comparison of the old and new ST_Y() values. > > > > If I force the PROJ 4 definition to be used, the transformation works > > fine with no shift. (To force the PROJ 4 definition, I used the method > > described in > > http://blog.cleverelephant.ca/2019/02/proj4-postgis.html and set > > authname, authsrid and srtext to null so that the proj4text column is > used.) > > > > Is this shift expected with PROJ 6? I realize 900913 is deprecated and > > we plan to migrate to 3857 as a longer term solution, but looking for > > a shorter term fix if possible since much data and code is impacted by > > this. Note we are seeing no shift issues with SRID 3857. > > > > Let me know if I can provide more information. > > > > Thanks much, > > Shira > > > > _______________________________________________ > postgis-users mailing list > [email protected] > https://lists.osgeo.org/mailman/listinfo/postgis-users
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