[postgis-users] Purpose of mesure value in 4D geoms

[Richard_D_Levine at raytheon.com]

postgis-users-bounces at 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?

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