[gdal-dev] WCS GetCoverage with AxisOrder swap

[Peter Baumann]

Even-

very good question:

On 11/09/2017 08:41 AM, Even Rouault 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>
>

In CIS 1.0 it _must_ be the axis name as given in the CRS's axisAbbrev element.
At some time, however, OGP informed the world (well: the WCS.SWG) that this is
not normative and they reserve to change it, which they did: "Long" -> "Lon".
After the dust around this rumble settled the mechanism (agreed between WCS.SWG
and CRS.SWG) was slightly relaxed for CIS 1.1: axisLabels can use _any_ unique
identifier (say, axisLabels="x1 x2 x3") and only its positional order defines
the mapping between the CRS axis and the coverage axis.

So, in CIS 1.0: exact string equality, CIS 1.1: "random" value.

-Peter

>  
>
> > 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
>

-- 
Dr. Peter Baumann
 - Professor of Computer Science, Jacobs University Bremen
   www.faculty.jacobs-university.de/pbaumann
   mail: p.baumann at jacobs-university.de
   tel: +49-421-200-3178, fax: +49-421-200-493178
 - Executive Director, rasdaman GmbH Bremen (HRB 26793)
   www.rasdaman.com, mail: baumann at rasdaman.com
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