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
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