Spatial Clustering of Introduction to postgis (2)

The previous article mainly introducedSt_snaptogrid. Now we use the features table in the previous articles for the following applications:

This section briefly describes the methods used:

GeometrySt_collect (Geometry[] G1_array); combines a series of geometries into a single st_geometry (the old version is called geometrycollection ).

GeometrySt_multi (GeometryG1); converts G1 to a multi * geometry.

As with the previous methods, connect to the database, open the query visualization box, and add the following SQL:

  select   st_multi (st_collect (the_geom ))   as   the_geom, st_astext (st_multi (st_collect (the_geom) 
   from   features 
   group     by   st_snaptogrid (st_transform (the_geom,   2327  ),   2000  ,  2000  )  

Aggregates points in features into a grid of 2000*2000 m²,St_transform (the_geom,2327) Is to convert the coordinate system from 4326 to 2327, because the measurement unit of 4326 is degree, 2327 (here I randomly find a Xi'an 80 COORDINATE SYSTEM) should be meters. St_astext (st_multi (st_collect (the_geom) is not very useful, but it is easy to edit styles in qgis.

Change the grid size to 5000*5000:

SelectSt_multi (st_collect (the_geom ))AsThe_geom, st_astext (st_multi (st_collect (the_geom )))
FromFeatures
Group BySt_snaptogrid (st_transform (the_geom,2327),5000,5000)