[postgis-users] ST_Transform troubles

[Mike Toews]

Hi Frans,

On 24 June 2011 02:56, Frans Knibbe <frans.knibbe at geodan.nl> wrote:
> About the order of coordinates: I see that PostGIS uses EPSG as the
> authority that defines coordinate reference systems. If you look up the
> definition of EPSG:4326 (for example at http://www.epsg-registry.org/, use
> 'retrieve by code'), you can see that it explicitly says that the axes are
> latitude, longitude. So it seems the standard that is used in PostGIS
> specifies (latitude, longitude), not (longitude, latitude).

Right, of course there are several "Standards" around. Ralf mentioned
the surveyor's convention, which I recall seeing "NEZ" (northing,
easting, elevation). In printed form, the order is almost always
"latitude, longitude", and I'm sure that convention is centuries
(millennia?) old. There is an ISO convention that specifies "latitude,
longitude" see http://en.wikipedia.org/wiki/ISO_6709

The Open Geospatial Consortium (formerly Open GIS) are the standards
organization for open source software, and PostGIS was certified
several years ago. Throughout all of their documentation for
coordinate order they use the Cartesian coordinate system for sake of
consistency. So a point must be defined in the order "X Y", regardless
of coordinate reference system. They actually do spell out "The
longitude is assumed to be the first ordinate, and the latitude is
assumed to be the second ordinate" in a rather old "OpenGIS
Implementation Specification: Coordinate Transformation Services"
document.

As for EPSG, they don't necessarily do anything with geospatial
formats and serialized output, but their documents are consistently in
the order "latitude, longitude", as you correctly pointed out.

-Mike