WCS Img_Sample - GridOrigin and GridOffsets appear flipped

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WCS Img_Sample - GridOrigin and GridOffsets appear flipped

Timothy Astle
Hi all,

I'm wondering if anyone noticed what I believe I'm seeing.  I am using the sample data provided with GeoServer 2.5.2.

/geoserver/ows?service=wcs&version=1.1.1&request=DescribeCoverage&identifiers=Img_Sample

<CoverageDescriptionSnip>
...
<wcs:GridCRS>
  <wcs:GridBaseCRS>urn:ogc:def:crs:EPSG::4326</wcs:GridBaseCRS
  <wcs:GridType>urn:ogc:def:method:WCS:1.1:2dGridIn2dCrs</wcs:GridType>
  <wcs:GridOrigin>-130.81666154628687 54.08616613712375</wcs:GridOrigin>
  <wcs:GridOffsets>0.07003690742624616 0.0 0.0 -0.05586772575250837</wcs:GridOffsets>
  <wcs:GridCS>urn:ogc:def:cs:OGC:0.0:Grid2dSquareCS</wcs:GridCS>
</wcs:GridCRS>
...
</CoverageDescriptionSnip>

The GridOrigin and GridOffsets are in long/lat ordering, not lat/long.

I double-checked the WCS 1.1 spec, and on page 89, it states that the GridOrigin and GridOffsets are in the GridBaseCRS.  Based on what I'm seeing, it looks like the GridOrigin and GridOffsets values are flipped.

The inverted values seem to be tripping up GDAL as a WCS client.

Any thoughts?


--
Tim Astle


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Re: WCS Img_Sample - GridOrigin and GridOffsets appear flipped

Jonathan Moules-2
Hi Tim,
I'm not that well versed in WCS, but taking a gander at the spec, to me at least it's non-obvious which order is "right".

On your noted page 89 it says lat/lon is correct for gml:GeographicCRS, but for wgs84BoundingBox it's lon/lat (page 18).
The examples on later pages (90 and 91) also seem to indicate lat/lon for GridOffsets, although that's using EPSG:63266405.

So it may be worth double-checking the EPSG and choosing a flavour that allows lat/lon or lon/lat as desired.
Cheers,
Jonathan



On 27 August 2014 19:42, Timothy Astle <[hidden email]> wrote:
Hi all,

I'm wondering if anyone noticed what I believe I'm seeing.  I am using the sample data provided with GeoServer 2.5.2.

/geoserver/ows?service=wcs&version=1.1.1&request=DescribeCoverage&identifiers=Img_Sample

<CoverageDescriptionSnip>
...
<wcs:GridCRS>
  <wcs:GridBaseCRS>urn:ogc:def:crs:EPSG::4326</wcs:GridBaseCRS
  <wcs:GridType>urn:ogc:def:method:WCS:1.1:2dGridIn2dCrs</wcs:GridType>
  <wcs:GridOrigin>-130.81666154628687 54.08616613712375</wcs:GridOrigin>
  <wcs:GridOffsets>0.07003690742624616 0.0 0.0 -0.05586772575250837</wcs:GridOffsets>
  <wcs:GridCS>urn:ogc:def:cs:OGC:0.0:Grid2dSquareCS</wcs:GridCS>
</wcs:GridCRS>
...
</CoverageDescriptionSnip>

The GridOrigin and GridOffsets are in long/lat ordering, not lat/long.

I double-checked the WCS 1.1 spec, and on page 89, it states that the GridOrigin and GridOffsets are in the GridBaseCRS.  Based on what I'm seeing, it looks like the GridOrigin and GridOffsets values are flipped.

The inverted values seem to be tripping up GDAL as a WCS client.

Any thoughts?


--
Tim Astle


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Re: WCS Img_Sample - GridOrigin and GridOffsets appear flipped

Timothy Astle
Thanks for the reply Jonathan.

I'm not sure if I follow your point, or maybe I didn't do a good job explaining what I'm seeing.

Why wouldn't the GridOrigin and GridOffsets not be in axis ordering of the coordinate system which defines the grid?  Else there would be no way in ever knowing the order of the coordinates.  The specification seems really clear about that.  On a general note, the schemas have element definitions for ordering depending on the element used, such as the wgs84BoundingBox you cited, but that doesn't apply in this case.

This is what I'd expect to see:

i.e., Lat / Lon (taken from Img_Sample)
<CoverageDescriptionSnip>
...
<wcs:GridCRS>
  <wcs:GridBaseCRS>urn:ogc:def:crs:EPSG::4326</wcs:GridBaseCRS
  <wcs:GridType>urn:ogc:def:method:WCS:1.1:2dGridIn2dCrs</wcs:GridType>
  <wcs:GridOrigin>-130.81666154628687 54.08616613712375</wcs:GridOrigin>
  <wcs:GridOffsets>0.07003690742624616 0.0 0.0 -0.05586772575250837</wcs:GridOffsets>
  <wcs:GridCS>urn:ogc:def:cs:OGC:0.0:Grid2dSquareCS</wcs:GridCS>
</wcs:GridCRS>
...
</CoverageDescriptionSnip>

i.e., X, Y (something I hacked together in this email as an example)
<CoverageDescriptionSnip>
...
<wcs:GridCRS>
  <wcs:GridBaseCRS>urn:ogc:def:crs:EPSG::2036</wcs:GridBaseCRS
  <wcs:GridType>urn:ogc:def:method:WCS:1.1:2dGridIn2dCrs</wcs:GridType>
  <wcs:GridOrigin>2297561 7678078</wcs:GridOrigin>
  <wcs:GridOffsets>0.5 0.0 0.0 -0.5</wcs:GridOffsets>
  <wcs:GridCS>urn:ogc:def:cs:OGC:0.0:Grid2dSquareCS</wcs:GridCS>
</wcs:GridCRS>
...
</CoverageDescriptionSnip>

So from what I can tell, it appears that this is a bug.

I've created GEOS-6635 describing this.

Thanks again for your reply,


Tim


On 29/08/2014 4:55 AM, Jonathan Moules wrote:
Hi Tim,
I'm not that well versed in WCS, but taking a gander at the spec, to me at least it's non-obvious which order is "right".

On your noted page 89 it says lat/lon is correct for gml:GeographicCRS, but for wgs84BoundingBox it's lon/lat (page 18).
The examples on later pages (90 and 91) also seem to indicate lat/lon for GridOffsets, although that's using EPSG:63266405.

So it may be worth double-checking the EPSG and choosing a flavour that allows lat/lon or lon/lat as desired.
Cheers,
Jonathan



On 27 August 2014 19:42, Timothy Astle <[hidden email]> wrote:
Hi all,

I'm wondering if anyone noticed what I believe I'm seeing.  I am using the sample data provided with GeoServer 2.5.2.

/geoserver/ows?service=wcs&version=1.1.1&request=DescribeCoverage&identifiers=Img_Sample

<CoverageDescriptionSnip>
...
<wcs:GridCRS>
  <wcs:GridBaseCRS>urn:ogc:def:crs:EPSG::4326</wcs:GridBaseCRS
  <wcs:GridType>urn:ogc:def:method:WCS:1.1:2dGridIn2dCrs</wcs:GridType>
  <wcs:GridOrigin>-130.81666154628687 54.08616613712375</wcs:GridOrigin>
  <wcs:GridOffsets>0.07003690742624616 0.0 0.0 -0.05586772575250837</wcs:GridOffsets>
  <wcs:GridCS>urn:ogc:def:cs:OGC:0.0:Grid2dSquareCS</wcs:GridCS>
</wcs:GridCRS>
...
</CoverageDescriptionSnip>

The GridOrigin and GridOffsets are in long/lat ordering, not lat/long.

I double-checked the WCS 1.1 spec, and on page 89, it states that the GridOrigin and GridOffsets are in the GridBaseCRS.  Based on what I'm seeing, it looks like the GridOrigin and GridOffsets values are flipped.

The inverted values seem to be tripping up GDAL as a WCS client.

Any thoughts?


--
Tim Astle


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