[postgis-users] unit

[Gilbert, Antoine]

I know the SRID

I was figuring given the SRID I could know the unit. I don't know what
reference system is used at each time. I only have a bunch of queries
with srid associated

-----Original Message-----
From: David Bitner [mailto:osgis.lists at gmail.com] 
Sent: January 23, 2006 4:46 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] unit

If you don't know the projection units, then you don't know anything
about how to reference them at all!

If you are just using PostGIS tables set up by someone else, in
PostGIS, you can look at a a geometry using astext(geom) this will
give you the srid for the given projection.  You can then look up that
srid to see what projection is and what the units are.  If the
SRID=-1, then you know nothing about the projection and any distance
that you are measuring is pretty much meaningless.

On 1/23/06, Gilbert, Antoine <AGilbert at korem.com> wrote:
> I wonder if there is a better way to achieve this, suppose you don't
> know the projection of a given geometry
>
> -----Original Message-----
> From: David Bitner [mailto:osgis.lists at gmail.com]
> Sent: January 23, 2006 3:53 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] unit
>
> The units that are returned are the units that the projection your
> data is in.  For example, if your data is in meters then the distance
> returned will be in meters to get your distance in kilometers, you
> could use this query Distance(geometry,geometry)/1000.
>
>
> On 1/23/06, Gilbert, Antoine <AGilbert at korem.com> wrote:
> >
> >
> >
> > Hi
> >
> >
> >
> > When you are using functions like Distance(geometry, geometry),
> withinh SQL
> > queries, does it exists an easy way to tell the system I want
> kilometer
> > units ?
> >
> >
> >
> > Antoine
> > _______________________________________________
> > postgis-users mailing list
> > postgis-users at postgis.refractions.net
> > http://postgis.refractions.net/mailman/listinfo/postgis-users
> >
> >
> >
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