I am using ST_ClusterDBSCAN to help cluster some building polygons. I am using the following SQL:
CREATE TABLE clusters AS SELECT ogc_fid, cid, wkb_geometry AS geom FROM ( SELECT ogc_fid, ST_ClusterDBSCAN(wkb_geometry, eps := 5, minpoints := 1) over () AS cid, wkb_geometry FROM building) sq;
When I check the results every feature has a cid even though there are no other features with the same cid, i.e a building is not within 5 metres of another.
Reading the docs, ST_ClusterDBSCAN should give a feature not within a cluster the value of null.
So I am not sure why this is happening.