[postgis-users] unit

[David Bitner]

If you want to always do your calculations in one particular
projection you could always use transform:
distance(transform(geom,srid),transform(geom2,srid))

On 1/24/06, Gilbert, Antoine <AGilbert at korem.com> wrote:
> I am aware of this
>
> I was just hoping that I could have access to some functions allowing me
> to do that kind of calculation easily.
>
> I'm used to MapXTreme Java, when you specify you are using for example
> an oracle spatial table as a layer, whatever the srid you told to
> MapXTreme, you have functions to extract distance between 2 points in
> the unit you want. I was wondering if I could do that given postgis.jar
> and the postgis SQL functions.
>
> Antoine
>
>
> -----Original Message-----
> From: David Bitner [mailto:osgis.lists at gmail.com]
> Sent: January 24, 2006 9:42 AM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] unit
>
> Yes, for geographic coordinates (latitude/longitude)
> distance(geometry) does not really mean anything useful at all.  Think
> about what one degree along the equator vs. one degree near the poles.
>  Using cartesian math, each distance is the same when in reality they
> are very different.  For angular coordinates, you need to use the
> angular measurements distance_spheroid and distance_sphere.
>
> On 1/24/06, Markus Schaber <schabi at logix-tt.com> wrote:
> > Hi, Gilbert,
> >
> > Gilbert, Antoine wrote:
> >
> > > 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 ?
> >
> > If your coordinates are in lat/long, than have a look at
> > distance_spheroid and distance_sphere, they give the distance in
> meters.
> >
> > Markus
> >
> > --
> > Markus Schaber | Logical Tracking&Tracing International AG
> > Dipl. Inf.     | Software Development GIS
> >
> > Fight against software patents in EU! www.ffii.org
> www.nosoftwarepatents.org
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