[gdal-dev] WMS supported SRS

Thu Sep 19 06:59:56 PDT 2024

Hi,
After re-thinking this topic, I also came to conclusion that using
BoundingBox tags will not be a satisfactory solution for GDAL users. Maybe
it will better than current, but still poor...
In my opinion the most flexible solution is to provide a list of supported
SRSs by a server, just like in *OGR_L_GetSupportedSRSList for WFS.*
Then add a helper function to generate a valid path for chosen layer
(subdataset), SRS from the list, and providing reprojection of bounding box
if needed (as Jukka suggested in last message in last sentence).
This ensures users to use the full capabilities of the server.

Best,
Michał Kowalczuk

pt., 13 wrz 2024 o 15:15 Rahkonen Jukka <jukka.rahkonen at maanmittauslaitos.fi>
napisał(a):

> Hi,
>
>
>
> GDAL is open source, of course you can open a feature request. It will
> then be implemented, closed, of left open eternally.
>
>
>
> What do you plan to write into the feature request? I think that using the
> CRS of the additional BoundingBox is a good default and best for the users
> when they want to get data in that CRS. But if they want to use data in
> some other CRS and their favorite CRS appears in some CRS list in the
> GetCapabilities, even without additional BoundingBox, then they should use
> that for communicating with the WMS server. That’s because the WMS server
> usually sends much better quality maps when it re-projects the source data
> for rendering, compared to the result that is achieved when GDAL warps the
> rasters that it if fetching with GetMaps in another CRS.
>
>
>
> So, after re-thinking your original idea about creating a subdataset from
> each supported CRS is good, but because of potentially thousands of
> subdatasets it may lead to some usability problems. I am not sure if there
> can be some problems in implementation as well. I see that GDAL shows the
> subdatasets with BBOX:
>
>
>
> SUBDATASET_26_NAME=WMS:
> http://localhost:8080/geoserver/ows?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&LAYERS=topp%3Atasmania_state_boundaries&CRS=CRS:84&BBOX=143.83482400000003,-43.648056,148.47914100000003,-39.573891
>
> However, usually there are additional BoundingBoxes only for some of the
> supported CRSs, and for the rest GDAL should probably warp the
> <EX_GeographicBoundingBox>.
>
>
> -Jukka Rahkonen-
>
>
>
>
>
> *Lähettäjä:* Michał Kowalczuk <michkowalczuk at gmail.com>
> *Lähetetty:* perjantai 13. syyskuuta 2024 15.12
> *Vastaanottaja:* Rahkonen Jukka <jukka.rahkonen at maanmittauslaitos.fi>
> *Kopio:* gdal-dev at lists.osgeo.org
> *Aihe:* Re: [gdal-dev] WMS supported SRS
>
>
>
> So, can I open a feature request?
>
>
>
> Best,
>
> Michal Kowalczuk
>
>
>
> W dniu czw., 12.09.2024 o 13:57 Rahkonen Jukka <
> jukka.rahkonen at maanmittauslaitos.fi> napisał(a):
>
> Hi,
>
>
>
> Your suggestion to utilize the additional layer BBOXes if they exist feels
> good to me, and better than to use the first advertised SRS from the root
> level. Beyond that what can be done with parsing the GetCapabilities is
> limited in my mind, because all projections which are supported may not be
> useful in real life.
>
>
>
> -Jukka Rahkonen-
>
>
>
> *Lähettäjä:* Michał Kowalczuk <michkowalczuk at gmail.com>
> *Lähetetty:* torstai 12. syyskuuta 2024 14.35
>
>
> *Vastaanottaja:* Rahkonen Jukka <jukka.rahkonen at maanmittauslaitos.fi>
> *Kopio:* gdal-dev at lists.osgeo.org
> *Aihe:* Re: [gdal-dev] WMS supported SRS
>
>
>
> So we remain at the point that there is no good method that, using only
> GDAL, will allow to fully use the WMS service without additional work
> related to XML parsing...?
>
>
>
> Best,
>
> Michał Kowalczuk
>
>
>
> wt., 10 wrz 2024 o 17:06 Michał Kowalczuk <michkowalczuk at gmail.com>
> napisał(a):
>
> A sample from your link:
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> *<Layer queryable="1" opaque="0"> <Name>Rakennustietoruudukko_2017</Name>
> <Title>Rakennustietoruudukko 2017</Title> <Abstract>Tietoa rakennuksista
> 250 x 250m ruudukoissa pääkaupunkiseudulla</Abstract> <KeywordList>
> <Keyword>features</Keyword> <Keyword>Rakennustietoruudukko_2017</Keyword>
> </KeywordList> <CRS>EPSG:3879</CRS> <CRS>CRS:84</CRS>
> <EX_GeographicBoundingBox>
> <westBoundLongitude>24.50112802448554</westBoundLongitude>
> <eastBoundLongitude>25.25849178466466</eastBoundLongitude>
> <southBoundLatitude>60.052265324029165</southBoundLatitude>
> <northBoundLatitude>60.39874702231777</northBoundLatitude>
> </EX_GeographicBoundingBox> <BoundingBox CRS="CRS:84"
> minx="24.50112802448554" miny="60.052265324029165" maxx="25.25849178466466"
> maxy="60.39874702231777"/> <BoundingBox CRS="EPSG:3879" minx="6659998.5"
> miny="2.5472498E7" maxx="6698499.5" maxy="2.551425E7"/> <Style>
> <Name>polygon</Name> <Title>Default polygon style</Title> <Abstract>A
> sample style that just draws out a solid gray interior with a black 1px
> outline</Abstract> <LegendURL width="20" height="20">
> <Format>image/png</Format> <OnlineResource xmlns:xlink="*
> *http://www.w3.org/1999/xlink* <http://www.w3.org/1999/xlink>*"
> xlink:type="simple" xlink:href="*
> *https://kartta.hsy.fi/geoserver/asuminen_ja_maankaytto/ows?service=WMS&version=1.3.0&request=GetLegendGraphic&format=image%2Fpng&width=20&height=20&layer=Rakennustietoruudukko_2017*
> <https://kartta.hsy.fi/geoserver/asuminen_ja_maankaytto/ows?service=WMS&version=1.3.0&request=GetLegendGraphic&format=image%2Fpng&width=20&height=20&layer=Rakennustietoruudukko_2017>
>
>
> *"/> </LegendURL> </Style> </Layer>*
>
>
>
> wt., 10 wrz 2024 o 17:05 Michał Kowalczuk <michkowalczuk at gmail.com>
> napisał(a):
>
> Ok, now I see the problem. Thank you Jukka for the explanation with a
> sample.
>
> So maybe we can use information from *BoundingBox*?
>
> and generate SUBDATASETS for each combination of Layer and BoundingBox
> definition that is usually defined for "best"/dedicated projections for a
> layer.
>
>
>
> *(7.2.4.6.8 )*
>
> *A Layer may have multiple BoundingBox elements, but each one shall state
> a different CRS (...)*
>
> *A Layer shall not provide a BoundingBox for a CRS it does not support.
> Conversely, a Layer may support CRSs*
>
> *for which it does not provide a BoundingBox: a server that has the
> ability to transform data to different CRSs may*
>
> *choose not to provide an explicit BoundingBox for every possible CRS
> available for each Layer. The server*
>
> *should provide BoundingBox information for at least the native CRS of the
> Layer (that is, the CRS in which the*
>
> *Layer is stored in the server’s database).*
>
>
>
> Best,
>
> Michał
>
>
>
> W dniu wt., 10.09.2024 o 16:07 Rahkonen Jukka <
> jukka.rahkonen at maanmittauslaitos.fi> napisał(a):
>
> Hi
>
>
>
>    - I meant to use CRSs only reported by GetCapabilities. I haven't seen
>    that GetCapabilities returns so many (6782) possible projections...
>
>
>
> I was meaning the same, CRSs reported in GetCapabilities. I used a search
> engine with phrase “service=WMS&version=1.3.0” and found in three minutes
> many examples, including this one
> kartta.hsy.fi/geoserver/asuminen_ja_maankaytto/ows?service=WMS&version=1.3.0&request=GetCapabilities.
> If you want to see more, install Geoserver on your computer and have a look
> at the default GetCapabilities.
>
>
>
> Finding the best CRS from WMS GetCapabilities is guesswork. The server
> above is a Finnish one so probably EPSG:3067 is the most native CRS because
> that is what we tend to use in Finland. However, there is also one and only
> one additional BBOX for EPSG:3879 in GetCapabilities, but that would be
> somewhat odd selection for a country-wide CRS. It is also possible that for
> example some CRS of New Zealand does not really work in GetMap of the
> Finnish data even GetCapabilities says it will. But when WMS is configured
> to show a short CRS list then I would trust that they are all good to use.
> Just be aware that the list can also be very long.
>
>
>
> If you start implementing the LIST_ALL_SRS option, it should be noted that
> the service level CRS list applies to all layers, and each layer can add
> more CRSs to the list. Maybe in theory there could be even
> “crs-list-of-service-root + crs-list-of-group-layer +
> crs-list-of-child-layer”.
>
>
>
> “7.2.4.6.7 CRS
>
> Every Layer is available in one or more layer coordinate reference
> systems. 6.7.3 discusses the Layer CRS. In
>
> order to indicate which Layer CRSs are available, every named Layer shall
> have at least one <CRS> element that
>
> is either stated explicitly or inherited from a parent Layer. The root
> <Layer> element shall include a sequence of
>
> zero or more CRS elements listing all CRSs that are common to all
> subsidiary layers. A child layer may optionally
>
> add to the list inherited from a parent layer. Any duplication shall be
> ignored by clients.
>
> When a Layer is available in several coordinate reference systems, the
> list of available CRS values shall be
>
> represented as a sequence of <CRS> elements, each of which contains only a
> single CRS name.”
>
>
>
> -Jukka Rahkonen-
>
>
>
>
>
>
>
>
>
> *Lähettäjä:* Michał Kowalczuk <michkowalczuk at gmail.com>
> *Lähetetty:* tiistai 10. syyskuuta 2024 16.32
> *Vastaanottaja:* Rahkonen Jukka <jukka.rahkonen at maanmittauslaitos.fi>
> *Kopio:* gdal-dev at lists.osgeo.org
>
>
> *Aihe:* Re: [gdal-dev] WMS supported SRS
>
>
>
> Thank you for your feedback. My comments are below:
>
>
>
> *It means that there are tens of thousands WMS services which support 6782
> different projections for each layer (checked from Geoserver version
> 2.25.3). I would not like them all to be reported as subdatasets.*
>
> I meant to use CRSs only reported by GetCapabilities. I haven't seen that
> GetCapabilities returns so many (6782) possible projections...
>
>
>
> *WMS standard also does not define any default CRS and the first one on
> the list in GetCapabilities does not need to be the best.*
>
> Therefore, the current form of the generating subdatasets names method for
> WMS driver is even more useless, if we have a non-default (not the best)
> projection for the data.
>
>
>
> And the only good way to work with it is to parse XML and generate paths
> manually...
>
>
>
> That's why I favor Even's option to introduce open option
> LIST_ALL_SRS=YES/NO.
>
>
>
> Any more thoughts?
>
>
>
> Michał Kowalczuk
>
>
>
> wt., 10 wrz 2024 o 15:03 Rahkonen Jukka <
> jukka.rahkonen at maanmittauslaitos.fi> napisał(a):
>
> Hi,
>
>
>
> WMTS typically supports a rather small number of tilematrices and tiles
> are usually cached, so it makes a lot of sense to advertise the available
> matrices and utilize them. On the other hand WMS maps are created
> on-the-fly and there is very low technical cost on the server side to
> support however many projections. WMS standard also does not define any
> default CRS and the first one on the list in GetCapabilities does not need
> to be the best.
>
>
>
> I guess that Geoserver is the most common WMS server in the world and
> amazingly many Geoservers run with the default settings. It means that
> there are tens of thousands WMS services which support 6782 different
> projections for each layer (checked from Geoserver version 2.25.3). I would
> not like them all to be reported as subdatasets.
>
>
>
> I can see that ogrinfo and the OGC API Features driver report the list of
> supported projections. Test with ogrinfo OAPIF:
> https://ogc-api.nrw.de/inspire-us-feuerwehr -al -so shows “Supported SRS:
> OGC:CRS84, EPSG:25832, EPSG:25833, EPSG:4258, EPSG:4326, EPSG:3395,
> EPSG:3857, EPSG:3034, EPSG:3035”
>
> Something similar might be an option for gdalinfo, but still about 6782
> EPSG codes per layer is too much to be viewed by default. Maybe the CRS
> list could be reported under some metadata domain that user could read on
> demand?
>
>
>
> -Jukka Rahkonen-
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> *Lähettäjä:* gdal-dev <gdal-dev-bounces at lists.osgeo.org> *Puolesta *Michal
> Kowalczuk via gdal-dev
> *Lähetetty:* tiistai 10. syyskuuta 2024 15.15
> *Vastaanottaja:* gdal-dev at lists.osgeo.org
> *Aihe:* Re: [gdal-dev] WMS supported SRS
>
>
>
> I found that there was a similar issue in 2021 without any specific answer:
>
> https://www.mail-archive.com/gdal-dev@lists.osgeo.org/msg35549.html
>
>
>
> I wonder if getting SUBDATASETS shouldn't return the result in a similar
> way as it does for WMTS service,
>
> where GDAL generates paths to all layer/tilematrix/tilematrixset
> combination.
>
> For example if layer is available in 3 SRS, GDAL produces 3 subdatasets,
> so using only SUBDATASE_NAME property user has access to all map services
> shared by WMTS server.
>
> In my opinion, GDAL should use the same approach for WMS.
>
>
>
> Does anyone object?
>
> I will then submit a new feature request/bug report.
>
>
>
> Best regards and have a nice day
>
> Michał Kowalczuk
>
>
>
> pon., 9 wrz 2024 o 16:17 Michał Kowalczuk <michkowalczuk at gmail.com>
> napisał(a):
>
> Hi,
>
> Does GDAL provides a method to get supported spatial reference systems by
> WMS service?
>
> *GDALGetMetadata(SUBDATASETS) *generate links only for the first
> (default) SRS from GetCapabilities, so this won't be helpful.
>
> Working with WFS I can get supported SRS using OGR
> *OGR_L_GetSupportedSRSList *function.
>
> Does GDAL offers something similar for WMS, or should I get this
> information from GetCapabilities XML by myself?
>
>
>
> Regards,
>
> Michal
>
>
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