Running clustering queries

[Daryl Herzmann]

On Thu, Mar 28, 2024 at 9:05 AM Regina Obe <lr at pcorp.us> wrote:
>
> > Depends where you got the data, but generally if they give you longitude
> > latitude Columns, then 4326 is a safe assumption and looks like you created
> > the geometry right too.
> >
> > To Gary's point, 4326 is degree based, so no wonder you aren't getting any
> > meaningful answers since 1000 would cover the whole world.
> >
> > SELECT city, state, ST_ClusterDBScan(geom, eps := 1000, minpoints :=
> > > >> 1) OVER () AS cluster FROM shapefiles.atp_filling_stations aa WHERE
> > > >> aa.amenity = 'fuel'
> > > >> AND aa.ctry_code = 'US' AND aa.geom IS NOT NULL;
> >
> > For US data, I have pretty good luck with US National Atlas Equal Area --
> > SRID=2163 which is a meter based coordinate system generally good enough
> > for accurate measurement.
> > Web Mercator is another but that is really bad for measure preserving
> >
> > But SRID=2163 is not common for display on maps etc, so I usually only use it
> > for good enough measurement preserving or as a functional index, not for
> > storage.
> >
> > I think your dataset is small enough that you can get away with on the fly
> > projection like below
> >
> >
> > SELECT city, state, ST_ClusterDBScan( ST_Transform(geom,2163), eps :=
> > 0.3048*500, minpoints :=1) OVER () AS cluster FROM
> > shapefiles.atp_filling_stations aa
> >       WHERE aa.amenity = 'fuel'
> > AND aa.ctry_code = 'US' AND aa.geom IS NOT NULL;
> >
>
> Slight amendment.  I guess 2163 is deprecated these days https://spatialreference.org/ref/epsg/2163/ , so the replacement is  9311
>
> https://spatialreference.org/ref/epsg/9311/
>
> Which I can't find in our spatial_ref_sys table (guess our table needs an update), but you can add with the below
> as long as you are using PostGIS 2.5 or higher and PROJ 7 or higher, it's going to relegate all the details to PROJ anyway
> So the other columns will not be needed except these 3.
>
> INSERT INTO spatial_ref_sys(srid, auth_name, auth_srid)
> VALUES(9311, 'EPSG', 9311);
>
>
> But anyway either should work I think with 2163 there was some issue with one of the proj settings which wouldn't impact
> your measurement but would affect proper display.

I stumbled into this issue today.  The lack of 9311 in
spatial_ref_sys.  Is a fix for this coming or is the spatial_ref_sys
just known to be stale and not getting updated with updated postgis
releases?

thanks
daryl