[wfs-dev] Axis Ordering in GML

[Simon Cox]

Not legal because it suggests a latitude of -172.335 when the permissible 
range for latitude in EPSG:4326 is 90:00:00.00S - 90:00:00.00N, etc etc.

Strictly this is *not* a GML issue - the gml:coordinates element is merely a 
character string, so the example is "valid" XML/GML.
Its just that the example given is strictly meaningless.
It is a "truth in advertising issue" - if you claim to be using a particular 
reference system, and then the value you provide is ill-formed & out of 
range, then you are *not* really using that CRS.

Unfortunately the three WFS's are telling porkies!
The sooner they stop then the sooner we could put this one to bed.

Simon

----- Original Message ----- 
From: "Paul Ramsey" <pramsey at refractions.net>
To: <Simon.Cox at csiro.au>
Cc: <wfs-dev at mail.opengeospatial.org>
Sent: Friday, May 20, 2005 10:21 PM
Subject: Re: [wfs-dev] Axis Ordering in GML


> Quick clarification:
>
>   Not legal in GML3 or in GML2 (WFS 1.0) or both?
>
> It is GML2 I am concerned about. I have results from three WFS servers so 
> far (Mapserver, Cubewerx, Intergraph) and all are returning 4326 data in 
> easting/northing order. A de facto implementation standard seems to be 
> emerging. I want to hear what implementors have done for WFS 1.0, if 
> possible!
>
> Thanks,
>
> Paul
>
> On 19-May-05, at 6:33 PM, <Simon.Cox at csiro.au> wrote:
>
>> No - it is not legal.
>> The main reason is the one you identify - as will all other coordinate
>> reference system definitions, EPSG 4326 does specify the axis order, and
>> as with all traditional geographic systems, the axis order is
>> latitude-longitude.
>> Furthermore, I think 4326 specifies DMSH as the encoding, though this
>> aspect might have been relaxed.
>> It is in fact not a GML issue, but is an EPSG issue.
>> GML inherits the rules provided by the organisation that are providing
>> the definition of the CRS.
>>
>> Two other issues:
>> 1. "EPSG:4326" is not a valid URI. In Document 05-010 OGC has defined a
>> URN scheme that is defined to refer to thing that you are trying to
>> point to. In this case it would be urn:ogc:def:crs:EPSG:6.3:4326
>> 2. the gml:coordinates element is deprecated in GML 3.0 and beyond. Use
>> gml:pos instead, with spaces between the components instead of comma.
>>
>> Simon
>>
>>> -----Original Message-----
>>> From: wfs-dev-bounces+simon.cox=csiro.au at opengeospatial.org
>>> [mailto:wfs-dev-bounces+simon.cox=csiro.au at opengeospatial.org]
>>>  On Behalf Of Paul Ramsey
>>> Sent: Thursday, 19 May 2005 11:50 PM
>>> To: wfs-dev at mail.opengeospatial.org
>>> Subject: [wfs-dev] Axis Ordering in GML
>>>
>>> Question for the group. Is the GML below legal?
>>>
>>> <gml:Point
>>> srsName="EPSG:4326"><gml:coordinates>-172.335,18.53916667</gml
>>> :coordinates></gml:Point>
>>>
>>> I have built a GML point that references EPSG:4326 but has
>>> the easting before the northing.
>>>
>>> If I check your WFS 1.0 servers, will I find them returning
>>> GML in easting/northing order or northing/easting order for
>>> EPSG:4326? This is both a theory and practice problem. In
>>> theory, what should happen, and in practice, what are people doing?
>>>
>>> Paul
>>> _______________________________________________
>>> wfs-dev mailing list
>>> wfs-dev at opengeospatial.org
>>> https://mail.opengeospatial.org/mailman/listinfo/wfs-dev
>>>
>