<div dir="ltr">Thanks Carl that is a great link. Can I confirm which "GeoServer" axis order page you wish corrected? <div><div>- <a href="http://docs.geoserver.org/latest/en/user/services/wfs/basics.html">http://docs.geoserver.org/latest/en/user/services/wfs/basics.html</a></div><div>- <a href="http://docs.geotools.org/latest/userguide/library/referencing/order.html">http://docs.geotools.org/latest/userguide/library/referencing/order.html</a></div></div><div><br></div><div>We have a release coming up and I would love to catch any corrections (and link to <a href="http://www.ogcnetwork.net/axisorder">http://www.ogcnetwork.net/axisorder</a>).<br></div></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div>--</div><div>Jody Garnett</div></div></div></div></div></div>
<br><div class="gmail_quote">On 19 October 2016 at 11:21, Carl Reed <span dir="ltr"><<a href="mailto:carl.n.reed@gmail.com" target="_blank">carl.n.reed@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div><div><div>Dear OSGeo community -<br><br></div>I have subscribed to the GeoServer list but have not yet been approved so I am posting to this list. <br><br></div>As you may know years ago I facilitates a lengthy and at time lively OGC discussion on Axis Order and CRS. The result of these discussions was OGC member approval of the OGC Axis Order policy and guidance (<a href="http://www.ogcnetwork.net/axisorder" target="_blank">http://www.ogcnetwork.net/<wbr>axisorder</a>).<br><br></div>Given this background, Esri recently approached me about some ambiguities and confusions regarding the history and evolution of how axis order was expressed in a Web Feature Service implementation instance. After review of various OGC WFS documents and discussions with the Editor (Peter Vretanos) I compiled the following information. I will be sharing the same information with the OGC Architecture Board and staff. Apparently, the CRS axis order issue never really "dies"!! <br><br></div>I bring this information to your attention so that perhaps the GeoServer community can update their WFS Axis Order web page content to be consistent with the following. Any questions in that regard, please let me know. Onto the discussion.<br><div><div><br><p class="MsoNormal" style="margin-bottom:12pt">Part of the
confusion is probably due to changing OGC policies over the last 15
years. Examples are the 2008 Axis Order Guidance policy (08-138r5) and
later the http uri policy (in TC
Policy Directives). Anyway, in 2013 the WFS 1.1.1 corrigendum corrected
the axis order issue to be consistent with the Axis Order policy as well
as other OGC standards. <br>
<br>
Short synopsis: Before WFS 1.1.1 the
only sure thing was that the axis order was LON/LAT when the notation
"EPSG:4326" was used to define the CRS and otherwise was undefined. For
WFS 1.1.1 and later, the OGC Axis Order policy
was in force which meant and still means that the axis order is defined
by the CRS being referenced, such as lat/lon for EPSG 4326.<br>
<br>
The longer answers is:<br>
<br>
How any WFS instance interprets axis order depends on the version of the
WFS standard implemented and the notation being used to specify the
CRS.<br>
<br>
Based on the WMS 1.0 model, WFS 1.0.0 used the notation EPSG:XXXX for
specifying CRSs. The implication was (although it was never explicitly
stated) that the WFS would do what WMS did and what the WMS did was to
say that for EPSG:4326 the axis order was LON/LAT.
This was actually also consistent with GML 2.1.1. For example:<br>
<br>
<gml:Box srsName="<a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__www.opengis.net_gml_srs_epsg.xml-234326&d=DQMFaQ&c=n6-cguzQvX_tUIrZOS_4Og&r=LCXhcrMdvdcRNz8NUgOEV1cYOakNFpC9sSTsSszC0Kc&m=HY5mDJJy4-L8dvfBgWuyrG9fxDiNEyFRZNZCetAE2kY&s=cz2ENba-ejcGrGosCxt7VCq5sYUHu7GlMCLq3G1jO2M&e=" target="_blank">http://www.opengis.ne<wbr>t/gml/srs/epsg.xml#4326</a>"><br>
<gml:coordinates>-180.0,-90.0 180.0,90.0</gml:coordinates><br>
</gml:Box><br>
<br>
The WMS 1.0 standard did not say anything about any other EPSG code and
so other CRS behavior was undefined. As a result, most WFS 1.0.0
implementations stuck with LON/LAT regardless of the EPSG code being
used.<br>
<br>
WFS 1.1.0 specified several notations for defining the CRS: EPSG:XXXX, <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__www.opengis.net_gml_src_epsg.xml-23XXXX&d=DQMFaQ&c=n6-cguzQvX_tUIrZOS_4Og&r=LCXhcrMdvdcRNz8NUgOEV1cYOakNFpC9sSTsSszC0Kc&m=HY5mDJJy4-L8dvfBgWuyrG9fxDiNEyFRZNZCetAE2kY&s=vcSZ-tEvudUXHYfE6HX2WUCkg5qjM9X5ULCLBSADUkw&e=" target="_blank">
http://www.opengis.net/gml/src<wbr>/epsg.xml#XXXX</a>,
urn:EPSG:geographicCRS:XXXX. The EPSG:XXXX notation was maintained for
backward compatibility with WFS 1.1. As such, a WFS implementation
instance would behave as it did in WFS 1.0.0 (i.e. LON/LAT for
EPSG:4326,
undefined otherwise). The other two notations were meant to follow the
then being developed OGC Axis Order policy which eventually provided
clear policy guidance on how to express and document axis order. The
recommended option is to use the axis order as
defined in the EPSG CRS definition. However, at the time WFS 1.1 was
being processed the Axis Order policy and notation were still in flux. Ultimately the URL and URN notations specified in the WFS
1.1 standard were invalid. This problem was,
however, addressed in the WFS 1.1.1 corrigendum. Unfortunately, for some reason that corrigendum was never published thereby increasing the WFS axis order confusion. This oversight is being addressed by OGC staff.<br>
<br>
Which brings us to WFS 1.1.1 and 2.0.X. In these versions, the same
Axis Order policy is specified: Do what the EPSG CRS definition says. Also,
at the same time the srsName expression changed to the http uri notation
(i.e.
<a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__www.opengis.net_dev_crs_epsg_0_xxxx&d=DQMFaQ&c=n6-cguzQvX_tUIrZOS_4Og&r=LCXhcrMdvdcRNz8NUgOEV1cYOakNFpC9sSTsSszC0Kc&m=HY5mDJJy4-L8dvfBgWuyrG9fxDiNEyFRZNZCetAE2kY&s=otM5bDnCQOb9DY-U_pSooY0tHUmXzTpcwfIOXZvwxyk&e=" target="_blank">
http://www.opengis.net/dev/crs<wbr>/epsg/0/xxxx</a>). This is because in
2010 the OGC policy changed regarding how to identify resources. The
OGC moved from urn's to using URLs as identifiers. Even so, the initial
version of WFS 2.0 used the URN notation
(urn:ogc:def:crs:EPSG:<ver>:XX<wbr>XX).
This changed in WFS 2.0.2 (corrigendum). All of the urn references were
changed to URLs with notes on what the older "urn" strings were.</p>
Which brings us to the
GeoServer documentation. That documentation is not quite right and
should be corrected to reflect reality and what is actually in the
various versions of the WFS
standards. Further, the GeoServer documentation mentions the use of
"urn:x-". I am not sure where that is coming from as none of the WFS
standards from WFS 1.0 and later use that notation.<br clear="all"><div><div><div><div><div><br></div><div>Regards<span class="HOEnZb"><font color="#888888"><br><br></font></span></div><span class="HOEnZb"><font color="#888888"><div>Carl<br></div><div>-- <br><div class="m_8645803394397860370gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr">Carl Reed, PhD<br></div><div>Carl Reed and Associates<br></div><div><br></div><div>Mobile: <a href="tel:970-402-0284" value="+19704020284" target="_blank">970-402-0284</a></div></div><div><p style="text-align:left;margin-top:6.24pt;margin-bottom:0pt;margin-left:0in;text-indent:0in;direction:ltr;word-break:normal"><font size="2" color="#000000"><span style="font-family:calibri">"When the power of love overcomes the love of power the world
will know </span><span style="font-family:calibri;font-weight:bold">peace</span><span style="font-family:calibri">." Jimi Hendrix</span></font></p></div></div></div></div></div></div></div>
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