[gdal-dev] WMS supported SRS

[Rahkonen Jukka]

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<mailto: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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