Hi,
I did not notice that reprojection happens. I had a look at the CRS extension
standard. First thing that it says is that range set values should not change
without CRS change.
“The GetCoverage request is extended with two optional parameters indicating
the CRSs for
subsetting coordinates and for the result coverage. If these parameters are
omitted then all
access will be performed in the coverage’s Native CRS (as reported in its
Coverage
Description).
Note This normally ensures that the coverage’s unchanged range set values are
retrieved, assuming
that no other operations than subsetting is performed in the GetCoverage
request.”
Then it says that server can do whatever it likes with resampling
“No statement is made in this specification about the interpolation method
applied by the
server in the course of the CRS transformation. A server is free to employ any
interpolation
method during CRS transformation, and information about the interpolation
applied may not
be accessible to the client. While the interpolation method applied may change
over requests,
and different interpolation methods may be applied to different range
components of a
particular coverage, a server should not change interpolation across the domain
of coverage
during execution of a single coverage CRS transformation.”
And this probably explains what should happen with extents and pixel size if
reader can interpret it (I couldn’t yet).
“The range values of the response to a successful GetCoverage request
containing an
outputCrs parameter shall be determined according to the following conceptual
evaluation model: Take the bounding box of the request’s subsetting parameter
(or the full
coverage bounding box if no subsetting was specified in the request);
re-project this
bounding box to the output CRS provided; generate the result image extent as
the smallest
bounding box around the reprojected subsetting box; fill this new image extent
with pixel
values re-projected from the coverage’s Native CRS to the output CRS in a way
that, for each
axis, the smallest distance between any two reprojected grid points is used as
offset
(including all interpolation and resampling necessary) unless specified
otherwise by further
request parameters.
Note Request parameters dictating a different behaviour wrt. grid point offset
are defined in the
WCS Scaling & Interpolation extension specification”
I have a feeling that without using those parameters from scaling and
interpolation extensions it is not at all guaranteed that the result is totally
predictable and identical for all WCS servers.
-Jukka Rahkonen-
Lähettäjä: andrea.a...@gmail.com [mailto:andrea.a...@gmail.com] Puolesta Andrea
Aime
Lähetetty: 11. elokuuta 2017 12:43
Vastaanottaja: Rahkonen Jukka (MML) <jukka.rahko...@maanmittauslaitos.fi>
Kopio: anna-lena.h...@bkg.bund.de; geoserver-users@lists.sourceforge.net
Aihe: Re: [Geoserver-users] WCS returns wrong GeoTiffs
On Fri, Aug 11, 2017 at 11:32 AM, Rahkonen Jukka (MML)
<jukka.rahko...@maanmittauslaitos.fi<mailto:jukka.rahko...@maanmittauslaitos.fi>>
wrote:
Hi,
I would have a try with SCALESIZE and SCALEEXTENT parameters of the scaling
extension https://portal.opengeospatial.org/files/12-039. In theory
GetCoverage should keep the native pixel size but it may be that GeoServer does
not really know what the native pixel size is.
I don't have an answer for the original question, but mind, there is
reprojection involved here, http://epsg.io/31467 is not UTM32N.
I don't believe there is in the spec a requirement to maintain the native
resolution in this case, but I may be wrong.
Cheers
Andrea
--
Regards,
Andrea Aime
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