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<div class="moz-cite-prefix">On 04/05/2017 02:16 PM, Andrea Aime
wrote:<br>
</div>
<blockquote
cite="mid:CA+nxMTu04=+k1HuZHdvX_URJHvO+PdmzN9EKihFmUoDSNNQkEQ@mail.gmail.com"
type="cite">
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<div class="gmail_quote">On Tue, Apr 4, 2017 at 12:24 PM,
Peter Baumann <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:p.baumann@jacobs-university.de"
target="_blank">p.baumann@jacobs-university.de</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF">
<p>To avoid the problems that other standards have with
axis order, coverages contain the axis order
explicitly, in the axisLabels attribute. Here an
example:<br>
</p>
<br>
<gml:Envelope srsName=<a
moz-do-not-send="true"
class="gmail-m_4675187607587398788moz-txt-link-rfc2396E"
href="http://www.opengis.net/def/crs/EPSG/0/4326"
target="_blank">"http://www.opengis.<wbr>net/def/crs/EPSG/0/4326"</a>
<b>axisLabels="Lat Long"</b> uomLabels="deg deg"
srsDimension="2"><br>
<gml:lowerCorner>1
1</gml:lowerCorner><br>
<gml:upperCorner>3
10</gml:upperCorner><br>
</gml:Envelope><br>
<br>
The sequence in axisLabels is indicative. </div>
</blockquote>
<div><br>
</div>
<div>I'm looking at the WCS 2.0.1 core spec, all it says
about the labels is:</div>
<div><br>
</div>
<div>"The attribute axisLabels is an ordered list of labels
for all the axes of this CRS". Label is a generic term, I
don't see any dictionary giving meaning to the labels.</div>
</div>
</div>
</div>
</blockquote>
<br>
srsName and axisLabels are inherited from GML 3.2.1 which says (cf
comment in geometryBasic0d1d.xsd):<br>
"The attribute axisLabels is an ordered list of labels for all the
axes of this CRS. The gml:axisAbbrev value should be used for these
axis labels, after spaces and forbidden characters are removed. When
the srsName attribute is included, this attribute is optional. When
the srsName attribute is omitted, this attribute shall also be
omitted."<br>
In GMLCOV/CIS axisLabels is mandatory.<br>
<br>
Purpose is to associate the EPSG CRS axes with the axes as used in
the XML document in a machine readable manner, without the
ambiguities of other standards. <br>
In CIS 1.0 this is via axisAbbrev, so quite rigid. Following long
and winding discussions with EPSG this has been changed in CIS 1.1
so that your examples 3 and 4 are allowed as well (identification by
position, not by name).<br>
<br>
<blockquote
cite="mid:CA+nxMTu04=+k1HuZHdvX_URJHvO+PdmzN9EKihFmUoDSNNQkEQ@mail.gmail.com"
type="cite">
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<div class="gmail_extra">
<div class="gmail_quote">
<div>So the following should all be equivalent to the
client, or not?</div>
<div><gml:Envelope srsName="<a moz-do-not-send="true"
href="http://www.opengis.net/def/crs/EPSG/0/4326">http://www.opengis.net/def/crs/EPSG/0/4326</a>"
axisLabels="Lat Long" uomLabels="deg deg"
srsDimension="2"><br>
</div>
</div>
</div>
</div>
</blockquote>
<br>
correct as per EPSG:4326<br>
<br>
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cite="mid:CA+nxMTu04=+k1HuZHdvX_URJHvO+PdmzN9EKihFmUoDSNNQkEQ@mail.gmail.com"
type="cite">
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<div class="gmail_extra">
<div class="gmail_quote">
<div><gml:Envelope srsName="<a moz-do-not-send="true"
href="http://www.opengis.net/def/crs/EPSG/0/4326">http://www.opengis.net/def/crs/EPSG/0/4326</a>"
axisLabels="a b" uomLabels="deg deg" srsDimension="2"><br>
</div>
<div><gml:Envelope srsName="<a moz-do-not-send="true"
href="http://www.opengis.net/def/crs/EPSG/0/4326">http://www.opengis.net/def/crs/EPSG/0/4326</a>"
axisLabels="foo bar" uomLabels="deg deg"
srsDimension="2"><br>
</div>
<div><gml:Envelope srsName="<a moz-do-not-send="true"
href="http://www.opengis.net/def/crs/EPSG/0/4326">http://www.opengis.net/def/crs/EPSG/0/4326</a>"
axisLabels="Long Lat" uomLabels="deg deg"
srsDimension="2"><br>
</div>
</div>
</div>
</div>
</blockquote>
<br>
all these are wrong in CIS 1.0, you _must_ use the axisAbbrev
element. In CIS 1.1 ok, although the last one is misleading.<br>
<br>
<blockquote
cite="mid:CA+nxMTu04=+k1HuZHdvX_URJHvO+PdmzN9EKihFmUoDSNNQkEQ@mail.gmail.com"
type="cite">
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<div class="gmail_quote">
<div><br>
</div>
<div>I added the last on purpose, since they are just
labels, they really carry no meaning, and the axis order
is still determined by the srsName instead (thus, lat
long).</div>
<div>Or not?</div>
</div>
</div>
</div>
</blockquote>
<br>
srsName and axisLabels are inherited from GML 3.2.1 which says (cf
comment in geometryBasic0d1d.xsd):<br>
"The attribute axisLabels is an ordered list of labels for all the
axes of this CRS. The gml:axisAbbrev value should be used for these
axis labels, after spaces and forbidden characters are removed. When
the srsName attribute is included, this attribute is optional. When
the srsName attribute is omitted, this attribute shall also be
omitted."<br>
In GMLCOV/CIS axisLabels is mandatory.<br>
<br>
<br>
<br>
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cite="mid:CA+nxMTu04=+k1HuZHdvX_URJHvO+PdmzN9EKihFmUoDSNNQkEQ@mail.gmail.com"
type="cite">
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<div class="gmail_quote">
<div> <br>
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<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF">So it is not necessary to use
GridFunctions for this purpose. My personal opinion is
that such mechanisms are not optimal for fiddling with
coordinate positions as they make it unnecessarily
difficult to determine the final pixel position. This
seems to be the case here as well. <br>
</div>
</blockquote>
<div><br>
</div>
<div>The function is there because we could not stomach the
idea that "i j" in raster space would be associated to up
and right (in this order), geographic coordinates systems
have their own madness (or at least OGC wants us to
believe that) but we hoped the raster space wouldn't be
touched. If we remove the function, keep the lat/lon
orientation for the envelope, and assume pairwise matching
like Jukka suggests, then this is our raster (aka pixel)
space:</div>
<div><br>
</div>
<div><img
src="cid:part7.EF0EA322.858073E2@jacobs-university.de"
alt="Inline image 2" height="228" width="220"> <br>
</div>
<div>It can work of course.</div>
<div><br>
</div>
<div>Then, since you are here, a question about the axis
order of the returned coverages (let's assume geotiff for
simplificity's sake). I am presuming some uniformity
across OGC standards, </div>
</div>
</div>
</div>
</blockquote>
<br>
that is the Holy Grail. In practice, groups work individually (which
is somehow understandable - it's all voluntary effort, although not
desirable - I have brought it to the doors of OGC many times that a
centralized point of coordination on the basics would be
advantageous; that point could be OWS Common which is under revision
since some time - not sure what this will mean in practice). <br>
<br>
<blockquote
cite="mid:CA+nxMTu04=+k1HuZHdvX_URJHvO+PdmzN9EKihFmUoDSNNQkEQ@mail.gmail.com"
type="cite">
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<div class="gmail_extra">
<div class="gmail_quote">
<div>so if vector data in WGS84 is to be returned in lat/lon
order, does it makes sense to return also coverages in the
same order? <br>
</div>
</div>
</div>
</div>
</blockquote>
<br>
as we seem to have EPSG as common ground, yes.<br>
<br>
<blockquote
cite="mid:CA+nxMTu04=+k1HuZHdvX_URJHvO+PdmzN9EKihFmUoDSNNQkEQ@mail.gmail.com"
type="cite">
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<div class="gmail_extra">
<div class="gmail_quote">
<div>Projection unaware software displays vector data
flipped when returned by a compliant WFS 1.1 server...
shouldn't it happen the same for WCS 2.0? Or should
rasters be considered somehow blessed and outside of this
issue?</div>
</div>
</div>
</div>
</blockquote>
<br>
I am always for harmonization (principle of least surprise in
Software Engineering), but you will find wildly varying opinions on
this :) <br>
<br>
HTH,<br>
Peter<br>
<br>
<br>
<blockquote
cite="mid:CA+nxMTu04=+k1HuZHdvX_URJHvO+PdmzN9EKihFmUoDSNNQkEQ@mail.gmail.com"
type="cite">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">
<div><br>
</div>
<div>Cheers</div>
<div>Andrea</div>
</div>
<div><br>
</div>
-- <br>
<div class="gmail_signature">
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<div>
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<div dir="ltr">
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<div>
<div>
<div>==</div>
<div>GeoServer Professional Services
from the experts! Visit</div>
<div><a moz-do-not-send="true"
href="http://goo.gl/it488V"
target="_blank">http://goo.gl/it488V</a>
for more information.</div>
<div><span style="font-size:12.8px">==</span><br>
</div>
</div>
<div><br>
</div>
</div>
<div>Ing. Andrea Aime <br>
</div>
<div>@geowolf</div>
<div>Technical Lead</div>
<div><br>
</div>
<div><span style="font-size:12.8px">GeoSolutions
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+39 0584 962313</span><br>
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target="_blank">http://twitter.com/geosolutions_it</a></div>
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</blockquote>
<br>
<pre class="moz-signature" cols="80">--
Dr. Peter Baumann
- Professor of Computer Science, Jacobs University Bremen
<a class="moz-txt-link-abbreviated" href="http://www.faculty.jacobs-university.de/pbaumann">www.faculty.jacobs-university.de/pbaumann</a>
mail: <a class="moz-txt-link-abbreviated" href="mailto:p.baumann@jacobs-university.de">p.baumann@jacobs-university.de</a>
tel: +49-421-200-3178, fax: +49-421-200-493178
- Executive Director, rasdaman GmbH Bremen (HRB 26793)
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tel: 0800-rasdaman, fax: 0800-rasdafax, mobile: +49-173-5837882
"Si forte in alienas manus oberraverit hec peregrina epistola incertis ventis dimissa, sed Deo commendata, precamur ut ei reddatur cui soli destinata, nec preripiat quisquam non sibi parata." (mail disclaimer, AD 1083)
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