[Geojson] [OSGeo-Standards] EPSG + Coordinate Ordering (Was Re:GeoJSON '1.0'?)

Carl Reed creed at opengeospatial.org
Thu Mar 13 16:50:27 PDT 2008

Not to be a bother, but Please wait until I send you the axis order guidance 
document the OGC has been working hard on. You may find the document useful 
and we would encourage your feedback.

Axis order is a non-trivial element of any geo application and the 
implications of having different approaches to dealing with CRS and axis 
order in different communities will be deadly in terms of consistency, data 
sharing, and interoperability in general.

And just to make things interesting, remember that a CRS does not have to be 
related to the earth :-)

Also, read  http://www.ogcnetwork.net/node/338 which provides excellent 
grounding as to what happens to the same "point" on the surface of the earth 
when different datums are used. One more reason using full CRS metadata such 
as defined in the EPSG database is so important.

Oh yeah, I forgot - (x,y,z) in South Africa is typically defined using 
reverse Lo-Gauss, which means that they use an upside down coordinate system 
(at least from us Northerners perspective). In other words, y "is directed 
south and not north.



----- Original Message ----- 
From: "Frank Warmerdam" <warmerdam at pobox.com>
To: "Christopher Schmidt" <crschmidt at metacarta.com>
Cc: <geojson at lists.geojson.org>; <standards at lists.osgeo.org>; "Paul Ramsey" 
<pramsey at cleverelephant.ca>
Sent: Thursday, March 13, 2008 5:41 PM
Subject: Re: [Geojson] [OSGeo-Standards] EPSG + Coordinate Ordering (Was 
Re:GeoJSON '1.0'?)

> 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.
> Chris,
> No offence, but "x, y, z" is not as specifically meaningful as you might
> think.  Do you mean "easting, northing, elevation"?  There are real 
> coordinate
> systems that routinely encoding x as southing, and y and westing
> (for instance).
> Best regards,
> -- 
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam, 
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | President OSGeo, http://osgeo.org
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