[wfs-dev] Axis Ordering in GML

Fri May 20 11:46:17 EST 2005

On May 20, 2005, at 12:23, Paul Ramsey wrote:

> True, but if we consider consistent axis ordering (under any scheme  
> at all!) a proper part of interoperability (and we *should*!) then  
> the CITE tests should exercise that! And they don't! So it is  
> possible for non-interoperable implementations to pass CITE!

But we've already found out that CITE doesn't test interoperability,  
nor does it test conformance to the spec. It tests compliance to the  
*profile* of the spec that was defined for the test itself. See this  
excerpt from wms.rwg:

On Jan 31, 2005, at 11:42, Morris, Charles, E. wrote:

 > Allan Doyle wrote:
 >>>
 >>>  1- To be certifiable as a BASIC WMS, an
 >>>  implementation must meet the following requirements:
 >>> ·It must support image/png or image/gif for GetMap
 >>> requests.
 >>
 >> This is a shortcoming in the conformance test. The WMS spec does not
 >> require either of these formats.
 >>
 >
 > I think there are some misunderstandings here.  The compliance test
 > requirements do not modify the WMS spec.  What they do is define
 > profiles of WMS implementations.  To meet the profile somewhat
 > arbitrarilly called "BASIC", the implementation must support PNG or
 > GIF.  This doesn't imply that implementations that don't meet this
 > requirement aren't conformant to the WMS spec.

So all is not lost. The testers could (should?) define a test that  
ensures interoperability!

     Allan

>
> Paul
>
> PS - Funny note: check out the GML data for the WMS CITE tests. It  
> follows the axis ordering specified in the embedded EPSG reference,  
> which is northing/easting.
>
> Morris, Charles, E. wrote:
>
>
>> All the WFS test data for CITE uses EPSG:32615 so the CITE tests
>> really don't shed any light on the EPSG:4326 interpretation
>> controversy.
>> Chuck Morris Northrop Grumman IT, TASC
>> -----Original Message----- From:
>> wfs-dev-bounces+chuck.morris=ngc.com at opengeospatial.org  
>> [mailto:wfs-dev-bounces+chuck.morris=ngc.com at opengeospatial.org]On  
>> Behalf Of Paul Ramsey Sent: Friday, May 20, 2005 11:07 AM To: Simon
>> Cox Cc: wfs-dev at mail.opengeospatial.org Subject: Re: [wfs-dev] Axis
>> Ordering in GML
>> Geoserver also does the "wrong" thing. Geoserver passes the CITE
>> tests. Geoserver is therefore (as far as the implementors can tell)
>> "conformant".
>> This detail of implementation is sufficiently obscure that
>> implementors seem to be universally failing to do it. So either the
>> specs need a big red warning message on the front, or the OGC needs
>> to adopt the implementation bias (easting/northing) as official and
>> (again) say so in every spec.
>> I really could care less about the issue in terms of which way is the
>>  "one true way" I just want everyone to implement the same damn thing
>> so I can write a client that interoperates with everybodies servers
>> and doesn't need special-cases to determine the vendor and behavior
>> for every WFS under the sun.
>> P.
>> Simon Cox wrote:
>>
>>> 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
>>>>>>
>>> _______________________________________________ wfs-dev mailing
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-- 
Allan Doyle
+1.781.433.2695
adoyle at intl-interfaces.com