Hi Jukka,
thanks for the explanation. I would like to add one more bit about the
meaning of the target bbox: the output
coverage must be contained in it, but it does not have to match it.
This is by specification, although it's not so clear to read:
"The result coverage shall contain only those range values of the original
coverage which lie within the effective lower and upper bound, obtained as
described."
Maybe a picture makes it more evident. Say we are just doing subsetting,
without reprojection, and the bbox is
like in this case using arbitrary positions (e.g, not perfectly matching
the original pixels).
In the following picture:
- The squares are the original pixels
- The dashed red rectangle is the requested area
- The green pixels is what the server should return, e.g., not resample
pixels to match the requested bounding box, but return the maximum set of
pixels contained in the requested bbox instead
[image: Inline image 1]
Regards
Andrea
On Fri, Aug 11, 2017 at 3:24 PM, Rahkonen Jukka (MML) <
jukka.rahko...@maanmittauslaitos.fi> wrote:
> Hi,
>
>
>
> The native pixel size in UTM32N is obviously 5.00 m. UTM projection is
> using a scale factor of 0.9996 and if you convert a polygon of size 5x5 m
> (presenting one pixel) into EPSG:31467 it will grow into
> 5.0020008x5.0020008 meters. That process is converting each pixel as they
> are without any resampling. If exact pixel size of 5 meters in EPSG:31467
> is to be achieved the data must be resampled. I would say that Geoserver is
> doing the right thing when it does minimum amount of resampling and allows
> pixel size to change. BTW. for example gdalwarp is doing the same thing and
> there are a bunch of questions about that in gis.stackexchange.
>
>
>
> Now if we consider that it is OK to have 5.0020008 pixel size in the
> output it is impossible to keep extent as 3400000, 5660000 to 3420000,
> 5680000 because you can’t fill such an area with 5.0020008x5.0020008 sized
> blocks.
>
>
>
> So if we want to keep what I consider as the most native pixel size
> 5.0020008 we can’t get exactly 3400000, 5660000 to 3420000, 5680000 as
> extent. If we want the extent to be exact we must generate 5 m sized pixels
> which means resampling because of the difference in the projections (the
> 0.9996 scale factor).
>
>
>
> I suppose it would be more clear is you re-projected data from UTM into
> EPSG:4326 because then it would be self-evident that the pixels size of the
> output is not 0.5 meters anymore because the unit is degrees.
>
>
>
> By using scaling extension you can force resampling into 5 m output pixels
> and with those you can fill your desired area 3400000, 5660000 to 3420000,
> 5680000.
>
>
>
>
>
> -Jukka-
>
>
>
>
>
>
>
> *Lähettäjä:* anna-lena.h...@bkg.bund.de [mailto:anna-lena.h...@bkg.bund.de]
>
> *Lähetetty:* 11. elokuuta 2017 15:40
> *Vastaanottaja:* andrea.a...@geo-solutions.it
> *Kopio:* Rahkonen Jukka (MML) <jukka.rahko...@maanmittauslaitos.fi>;
> geoserver-users@lists.sourceforge.net
> *Aihe:* AW: [Geoserver-users] WCS returns wrong GeoTiffs
>
>
>
> Hello Andrea,
>
>
>
> yes, I did. But I send it again:
>
>
>
> I requested in GK3:
>
> SUBSET=Y,http://www.opengis.net/def/crs/EPSG/0/31467(
> 3400000,3420000)&SUBSET=X,http://www.opengis.net/def/
> crs/EPSG/0/31467(5660000,5680000)
>
> AND set the crs to be the same:
>
> &SUBSETTINGCRS=http://www.opengis.net/def/crs/EPSG/0/31467
>
> &OUTPUTCRS=http://www.opengis.net/def/crs/EPSG/0/31467
>
>
>
> Should be 3400000, 5660000 to 3420000, 5680000
>
>
>
> But GeoServer returned:
>
> 3399999.6508074491284788,5659999.2086437549442053 :
> 3419997.6992640472017229,5680002.2594826966524124
>
>
>
> I just don’t understand why the extent is wrong AND the pixel size and
> dimension. I understand that there are different distortions depending on
> the projection.
>
> But how could I get the bounding box I requested?
>
>
>
> @Jukka: Thanks for the hint with the Scaleextent – I give it a try… I just
> wanted to avoid to clip the image again to the requested extend.
>
>
>
> *Von:* andrea.a...@gmail.com [mailto:andrea.a...@gmail.com
> <andrea.a...@gmail.com>] *Im Auftrag von *Andrea Aime
> *Gesendet:* Freitag, 11. August 2017 14:04
> *An:* Hock, Anna-Lena <anna-lena.h...@bkg.bund.de>
> *Cc:* Rahkonen Jukka (MML) <jukka.rahko...@maanmittauslaitos.fi>;
> GeoServer Mailing List List <geoserver-users@lists.sourceforge.net>
> *Betreff:* Re: [Geoserver-users] WCS returns wrong GeoTiffs
>
>
>
> On Fri, Aug 11, 2017 at 1:45 PM, <anna-lena.h...@bkg.bund.de> wrote:
>
> As far as I can interpret this, it means that in case we have OUTPUTCRS
> equals SUBSETTINGCRS the extent of the image should be exactly the one
> requested in SUBSET. The request coordinates aren’t transformed – the
> bounding box is “fixed” and the image is filled in this extent. If you vary
> the dimension and the size, then it should be possible to keep the
> requested extent. Am I missing something here?
>
>
>
> Hum... you did not provide the output bounding box, in your first mail you
> were concerned about the resolution and pixel width/height only no?
>
> What bounding box did GeoServer return?
>
>
>
> During reprojection with no target resolution normally one can choose to
> respect either the native resolution (it seems GeoServer did,
>
> to the letter, taking into account the different scaling factor of the two
> projections) or the target bounding box, but it's impossible in
>
> general to do both.
>
> Looking again at the specification extracts from Jukka I don't see a
> indication that one should be preferred over the other, looks
>
> like an implementation decision.
>
>
>
> Cheers
>
> Andrea
>
>
>
> --
>
> Regards,
>
> Andrea Aime
>
> ==
> GeoServer Professional Services from the experts! Visit
> http://goo.gl/it488V for more information.
> ==
>
> Ing. Andrea Aime
> @geowolf
> Technical Lead
>
> GeoSolutions S.A.S.
> Via di Montramito 3/A
> 55054 Massarosa (LU)
> phone: +39 0584 962313 <+39%200584%20962313>
> fax: +39 0584 1660272 <+39%200584%20166%200272>
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>
> http://www.geo-solutions.it
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>
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--
Regards,
Andrea Aime
==
GeoServer Professional Services from the experts! Visit http://goo.gl/it488V
for more information.
==
Ing. Andrea Aime
@geowolf
Technical Lead
GeoSolutions S.A.S.
Via di Montramito 3/A
55054 Massarosa (LU)
phone: +39 0584 962313
fax: +39 0584 1660272
mob: +39 339 8844549
http://www.geo-solutions.it
http://twitter.com/geosolutions_it
AVVERTENZE AI SENSI DEL D.Lgs. 196/2003
Le informazioni contenute in questo messaggio di posta elettronica e/o
nel/i file/s allegato/i sono da considerarsi strettamente riservate. Il
loro utilizzo è consentito esclusivamente al destinatario del messaggio,
per le finalità indicate nel messaggio stesso. Qualora riceviate questo
messaggio senza esserne il destinatario, Vi preghiamo cortesemente di
darcene notizia via e-mail e di procedere alla distruzione del messaggio
stesso, cancellandolo dal Vostro sistema. Conservare il messaggio stesso,
divulgarlo anche in parte, distribuirlo ad altri soggetti, copiarlo, od
utilizzarlo per finalità diverse, costituisce comportamento contrario ai
principi dettati dal D.Lgs. 196/2003.
The information in this message and/or attachments, is intended solely for
the attention and use of the named addressee(s) and may be confidential or
proprietary in nature or covered by the provisions of privacy act
(Legislative Decree June, 30 2003, no.196 - Italy's New Data Protection
Code).Any use not in accord with its purpose, any disclosure, reproduction,
copying, distribution, or either dissemination, either whole or partial, is
strictly forbidden except previous formal approval of the named
addressee(s). If you are not the intended recipient, please contact
immediately the sender by telephone, fax or e-mail and delete the
information in this message that has been received in error. The sender
does not give any warranty or accept liability as the content, accuracy or
completeness of sent messages and accepts no responsibility for changes
made after they were sent or for other risks which arise as a result of
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