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);
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.
PostGIS 2.2.0 came out this month, and the SFCGAL extension that offers advanced 3D and volumetric support, in addition to some extended 2D functions like
ST_ApproximateMedialAxis became a standard PostgreSQL extension
and seems to be a fairly popular extension.
I’ve seen several reports on GIS Stack Exchange of people trying to install PostGIS SFCGAL and getting things such as
ERROR: could not open extension control file /Applications/Postgres.app/Contents/Versions/9.5/share/postgresql/extension/postgis_sfcgal.control
as in this question: SFCGAL in PostGIS problem.
There are two main causes for this:
I’ve been asked this question in some shape or form at least 3 times, mostly from people puzzled why they get this error. The last iteration went something like this:
I can’t use
ST_AsPNG when doing something like
SELECT ST_AsPNG(rast) FROM sometable;
Gives error: Warning: pg_query(): Query failed: ERROR: rt_raster_to_gdal: Could not load the output GDAL driver.