[Geoserver-users] cascading wms and native crs

GeoServer GeoServer User
1

Hi,

I have not understood the meaning of advertised BBOXes from the remote server. For what Geoserver is using that information?

I believe that most WMS servers do not advertise bounding boxes for all the supported projections, the most famous example is just Geoserver http://demo.opengeo.org/geoserver/wms?service=WMS&request=GetCapabilities&version=1.3.0. Mapserver by default is advertising also BBOX only for the first supported SRS but it can be extended by a configuration option.

I have not thought thoroughly but my feeling is that WMS clients should not care about advertised BBOXes but that is probably because I run Mapserver which believes whatever layer extents I manually write into the mapfile and they are systematically inaccurate and often totally wrong, I fear. WMS servers send empty maps very fast if WMS client is sending BBOX which is outside the data area. However, I can imagine that sometimes, for some servers, there can be more trouble if client is sending a BBOX-SRS combination that does not work because re-projection with those values is impossible.

I suppose that the native SRS has meaning only when Geoserver must re-project map images on the server side when client asks for such SRS which is not supported by the remote server. Otherwise it is forwarding GetMaps by using the same SRS that was used in the client request. And when server side re-projecting is needed it would be best for the image quality to fetch maps from the remote server in the native projection of the data for preventing double-re-projecting. Often the native SRS is the first advertised SRS in GetCapabilities and therefore I think it would be better to use the first advertised SRS of the remote server as the native SRS than EPSG:4326. At least the quality of all Finnish and Norwegian raster maps would suffer badly if they would be squeezed into EPSG:4326 before the second re-projection.

-Jukka Rahkonen-

Tore Halset wrote:

On 29 Sep 2014, at 09:10, Andrea Aime <andrea.aime@anonymised.com> wrote:

> We could back transform each bbox to wgs84 and pick the largest one,
> yet, the reprojection itself back and forth can make bboxes larger
> each way one goes around (because of the rotation and the fact that
> the tilted reprojected bbox is turned into another axis parallel
> bbox), so reprojected bboxes migth look larger than a "original" wgs84 one.
>
> I'm leaning towards keeping things simple and just pick the first bbox
> in the list. Would that work in your case?

Picking the first is fine for me as I can tune the capabilities myself. However,
choosing the box for EPSG:4326 would be a more logical (IMO) choice. And
layer.getBoundingBoxes() return a HashMap, so we will have to dig a bit deeper
to find the *first* than just adding a "break;".

Regards,
Tore Halset.

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2

Hello.

On 29 Sep 2014, at 09:58, Rahkonen Jukka (Tike) <jukka.rahkonen@anonymised.com> wrote:

I have not understood the meaning of advertised BBOXes from the remote server. For what Geoserver is using that information?

At least for the wizard to set up cascading.

I believe that most WMS servers do not advertise bounding boxes for all the supported projections, the most famous example is just Geoserver http://demo.opengeo.org/geoserver/wms?service=WMS&request=GetCapabilities&version=1.3.0. Mapserver by default is advertising also BBOX only for the first supported SRS but it can be extended by a configuration option.

Not all, but some. Your example publishes bounding box for two coordinate systems. Mine has some more, but still not all. I would like to not have the bounding box in there, but some strange WMS clients require it for some coordinate systems. It is working fine. No stress. Only problem so far has been with GeoServer cascading.

- Tore.

3

On Mon, Sep 29, 2014 at 10:06 AM, Tore Halset <halset@anonymised.com> wrote:

Not all, but some. Your example publishes bounding box for two coordinate
systems. Mine has some more, but still not all. I would like to not have
the bounding box in there, but some strange WMS clients require it for some
coordinate systems. It is working fine. No stress. Only problem so far has
been with GeoServer cascading.

You're aware that you can also change the EPSG code and the bbox for any
layer, manually, to whatever value you want?
The pre-filling of the layer form is a convenience

Cheers
Andrea

--

GeoServer Professional Services from the experts! Visit
http://goo.gl/NWWaa2 for more information.

Ing. Andrea Aime
@geowolf
Technical Lead

GeoSolutions S.A.S.
Via Poggio alle Viti 1187
55054 Massarosa (LU)
Italy
phone: +39 0584 962313
fax: +39 0584 1660272
mob: +39 339 8844549

http://www.geo-solutions.it
http://twitter.com/geosolutions_it

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4

On Mon, Sep 29, 2014 at 9:58 AM, Rahkonen Jukka (Tike) <
jukka.rahkonen@anonymised.com> wrote:

I have not thought thoroughly but my feeling is that WMS clients should
not care about advertised BBOXes but that is probably because I run
Mapserver which believes whatever layer extents I manually write into the
mapfile and they are systematically inaccurate and often totally wrong, I
fear. WMS servers send empty maps very fast if WMS client is sending BBOX
which is outside the data area. However, I can imagine that sometimes, for
some servers, there can be more trouble if client is sending a BBOX-SRS
combination that does not work because re-projection with those values is
impossible.

Hi Jukka,
the main reason to guess the native SRS is just an accuracy one, most
GeoServer clients pick the first bbox we publish as the native
one, and if that is correct, you get less distortion in your output, either
because you're doing less resampling operations on your
raster data, or for vector data, because you're avoiding potential datum
shifts that can also incur in severe errors.

The second one is of course the convenience, in Tore's case he's not
getting the full bbox in the form by default, but just half of it

Cheers
Andrea

--

GeoServer Professional Services from the experts! Visit
http://goo.gl/NWWaa2 for more information.

Ing. Andrea Aime
@geowolf
Technical Lead

GeoSolutions S.A.S.
Via Poggio alle Viti 1187
55054 Massarosa (LU)
Italy
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
e-mail transmission, viruses, etc.

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