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List:       postgis-users
Subject:    Re: [postgis-users] Purpose of mesure value in 4D geoms
From:       strk () refractions ! net
Date:       2005-04-22 13:42:33
Message-ID: 20050422134233.GF19448 () freek ! keybit ! net
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On Fri, Apr 22, 2005 at 08:38:22AM -0500, Richard_D_Levine@raytheon.com wrote:
> 
> 
> postgis-users-bounces@postgis.refractions.net wrote on 04/22/2005 07:36:49
> AM:
> 
> > On Fri, Apr 22, 2005 at 01:58:15PM +0200, Markus Schaber wrote:
> > > Hi, Jeremy,
> > >
> > > Jeremy Palmer schrieb:
> > >
> > > > Sorry if this seems to be a simple question but could someone explain
> > > > the use and purpose of the M value in the new lwgeom geometry
> structure.
> > >
> > > You can use it for lean storage of measured values if you record geo
> > > coded measured values. E. G. with an XYZM geometry you can record
> > > position and height above ground and air pressure, or with an XYM
> > > geometry you can store longitude, latitude and fuel level of a ship.
> > >
> > > The alternative is to use plain XY(Z) geometries and store the measured
> > > values into their own table columns.
> >
> > Be aware that the Z value of a XYZ will probably have defined semantic
> > in upcoming OGC standards.
> 
> Defined as what?  Altitude from Mean Sea Level perhaps?

Check out 99-402r2 from OGC. Best bet is crowling in this list
archives (or postgis-devel ones). See also doc/ZMSgeoms.txt in
postgis distribution, it refers to the former.

--strk;

> 
> Rick
> >
> > --strk;
> >
> > >
> > > Markus
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> 
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