[Geojson] [OSGeo-Standards] EPSG + Coordinate Ordering (Was Re: GeoJSON '1.0'?)
crschmidt at metacarta.com
Fri Mar 14 04:30:31 PDT 2008
On Thu, Mar 13, 2008 at 07:41:17PM -0400, Frank Warmerdam wrote:
> Christopher Schmidt wrote:
> >That was not the plan for GeoJSON. The additional flag would not change
> >the data in any way, all it would do would be to accept, and describe,
> >the mapping from EPSG:4326 to the way GeoJSON works. The spec was (is)
> >very clear that the coordinate order is *always* x, y, z.
> No offence, but "x, y, z" is not as specifically meaningful as you might
> think. Do you mean "easting, northing, elevation"? There are real
> systems that routinely encoding x as southing, and y and westing
> (for instance).
And the CRS definition explicitly defines what x, y, and z are in the GML
definition for the projection. This was brought up by mpd: he offered
as an example, which uses x, y as southing, westing:
However, I have not yet found a Cartesian CS definition which does not
define the mapping from the directions in the data to x, y: regardless
of what it means, data must pick *some* coordinate system, and in order
to understand it in the world, you will have to map it to a CRS. The CRS
explains what X, Y, Z means.
Is there some coordinate reference system for which this isn't true?
Everything I've seen defines a <CoordinateSystemAxis> <axisAbbrev /></>
which provides the association, but I'll admit I only picked out a few
esoteric projections and went based on those, and have way less
knowledge about the subject than you and many others do.
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