In mapping frameworks spatial coordinates are often in order of latitude and longitude. In spatial databases spatial coordinates are in x = longitude, and y = latitude.
If you accidentally loaded data as lat,lon, you can always fix the mistake
by using the
ST_FlipCoordinates function introduced in PostGIS 2.0.
An example use for geometry:
ALTER TABLE sometable ALTER COLUMN geom TYPE geometry(LineString,4326) USING ST_FlipCoordinates( geom)::geometry(LineString,4326);
ALTER TABLE sometable ALTER COLUMN geog TYPE geography(LineString,4326) USING ST_FlipCoordinates( geog::geometry)::geography(LineString,4326);
As of PostGIS 2.3, the postgis extension was changed to no longer allow relocation. All function calls within the extension are now schema qualified.
While this change fixed some issues with database restore, it created the issue of if you installed PostGIS in a schema other than the one you wanted to it is not intuitive how to move it to a different schema. Luckily there is a way to do this.
For this exercise, I will install PostGIS in the default schema and then demonstrate how to move it into another schema location.
You can run these steps using psql or pgAdmin or any other PostgreSQL tool you want.
The error ‘postgis.backend’ is already set comes up every so often in PostGIS mailing list. The issue arises often during or after an upgrade. I’ll go over causes for this I am aware of and how to fix.
The question goes something like this
After upgrading to Postgis 2.3 from 2.1, my server log is filled with these messages :
“WARNING ‘postgis.backend’ is already set and cannot be changed until you reconnect”
This raster question comes up quite a bit on PostGIS mailing lists and stack overflow and the best answer often involves
the often forgotten
ST_Reclass function that has existed since PostGIS 2.0.
People often resort to the much slower though more flexible
ST_MapAlgebra or dumping out
their rasters as Pixel valued polygons they then filter
with WHERE val > 90,
ST_Reclass does the same thing but orders of magnitude faster.