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Specifying a urn for the srsName parameter for a WFS GetFeatures request can be better, as it can enforce a stricter structure of the returned data. E.g. If I specify srsName=urn:ogc:def:crs:EPSG::4326 then I know that the service will return coordinates in lat, long order. If I just specify srsName=EPSG:4326 then the coords of returned features are sometimes in long, lat order.

So we would like to specify srsName=urn:ogc:def:crs:EPSG::4326 wherever possible! But some WFS services do not accept the urn format for the srsName parameter. Is there any way to determine whether this is supported from a GetCapabilities request?

I have thought to parse the GetCapabilities response and use the first option listed in a <wfs:DefaultSRS> or <wfs:OtherSRS> tag that includes "4326". If a WFS service supports urn format will this be specified in the DefaultSRS tag?

An excerpt from a GetCapabilities response for a server that does not support urn:

<wfs:DefaultSRS>EPSG:28355</wfs:DefaultSRS>
<wfs:OtherSRS>EPSG:7855</wfs:OtherSRS>
<wfs:OtherSRS>EPSG:4326</wfs:OtherSRS>

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If it's WFS version 2.0.0 (https://portal.ogc.org/files/?artifact_id=39967) it must support URN's for the srsName parameter.

7.9.2.4.4 srsName parameter

Servers that implement this International Standard shall be able to process srsName attribute values using the following format model:

urn:ogc:def:objectType:authority:version:<EPSG code> (see OGC 07-092r2)

In this format model, objectType shall have the value of "crs", authority shall have the value "crs" and the value is a placeholder for the actual EPSG code value.

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