[gdal-dev] WCS GetCoverage with AxisOrder swap

jratike80 jukka.rahkonen at maanmittauslaitos.fi
Thu Nov 9 01:36:49 PST 2017

Even Rouault-2 wrote
> Peter,
>> the axisLabels attribute determines axis order, and this in turn refers
>> to the
>> CRS definition behind the URL in srsName.
> Does the value of RectifiedGrid.axisLabels must be correlated with the one
> of the CRS,
> or can it be a "random" value ?
> For example, GeoServer has 
> <gml:RectifiedGrid>
> <gml:axisLabels>
> i j
> </gml:axisLabels>
> </gml:RectifiedGrid>
>> My team has analysed your report and says:
> Thanks but I'm afraid I'm even more confused now.
>> On 11/08/2017 02:56 PM, Bang Pham Huu wrote:
>> > I checked the result as I think it is like this
>> > 
>> > + GeoServer is correct with http://www.opengis.net/def/crs/EPSG/0/2393
>> as
>> > this one is X, Y so the offset vector is correct.
> In EPSG, http://www.opengis.net/def/axis/EPSG/0/48 = X = NORTH and 
> http://www.opengis.net/def/axis/EPSG/0/47 = Y = EAST. So this CRS has the
> "GIS-unfriendly" order.
> But if you consider
> <gml:Envelope srsName="http://www.opengis.net/def/crs/EPSG/0/2393"
> axisLabels="Y X" uomLabels="m m" srsDimension="2">
> <gml:lowerCorner>
> 6543350.381089335 3061592.6391462097
> </gml:lowerCorner>
> <gml:upperCorner>
> 7307056.899896299 3432141.361396798
> </gml:upperCorner>
> </gml:Envelope>
> and assume from the above that Y=EAST=6543350.381089335 and
> X=NORTH=3061592.6391462097 (lower corner values),
> this doesn't transform to a location in Finland.
> Whereas X=NORTH=6543350.381089335 and Y=EAST=3061592.6391462097 does
> transform to Finland
> So I think the axisLabels here is wrong, it should be axisLabels="X Y"
>> > 
>> > offsetVector1: X (positive), Y (negative)
>> > 
>> > offsetVector2: Y (negative), X (positive)
> Can't correlate the above reasoning about the sign of values with the
> actual output of
> https://msp.smartsea.fmi.fi/geoserver/wcs?SERVICE=WCS&REQUEST=DescribeCoverage&VERSION=2.0.1&COVERAGEID=smartsea__eusm2016-EPSG2393
> which is
> <gml:offsetVector srsName="http://www.opengis.net/def/crs/EPSG/0/2393">
> 0.0 20.00803035910304
> </gml:offsetVector>
> <gml:offsetVector srsName="http://www.opengis.net/def/crs/EPSG/0/2393">
> -20.00803035910304 0.0
> </gml:offsetVector>
> Given what you said about 
> <gml:GridFunction>
>  not applying to GeoTIFF output, then
> this would be correct since the above would express that the first axis
> (along the width of the image) of the GeoTIFF
> express positive easting space and the second axis (along height) express
> negative northing spacing (image north-up oriented)
> Even
> -- 
> Spatialys - Geospatial professional services
> http://www.spatialys.com
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Hi folks,

I think that it is extremely good to discuss about axisOrder, GridFunctions,
offsetVectors, axisLabels etc. because for sure we all want to build
interoperability between different WCS 2.0 implementations.
However, I think that this mailing list thread is rather making more
confusion than clarifying things. First, it is very hard to follow who wrote
what and when, and if that was an answer, then what was the question. And if
we make errors with our conclusions, or if we forget to think about all
aspects in out analyzes, it is very hard to clarify that on the mailing
list. We should have something like Google document or a wiki page as a

About incomplete analyzes, I feel that the Rasdaman team perhaps forgot to
check the GridFunction when they analyzed the offsetVectors.
In the Rasdaman case there is an axisOrder rule
axisOrder="+2 +1"
and offset vectors are
offsetVector srsName="http://ows.rasdaman.org/def/crs/EPSG/0/4326">-0.02 0
srsName="http://ows.rasdaman.org/def/crs/EPSG/0/4326">0 0.02

In the Mapserver case there is no axisOrder rule which meant that it is the
axisOrder="+1 +2"
and offset vectors are
offsetVector srsName="http://www.opengis.net/def/crs/EPSG/0/4326">0 0.004167
offsetVector srsName="http://www.opengis.net/def/crs/EPSG/0/4326">-0.004167

Doesn’t these two expressions lead to same result? Yes or no?

-Jukka Rahkonen-

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