[mapserver-dev] WMS GetStyles by CLASS GROUP

[jbo-ads]

Hi all,

Adding a STYLES parameter to a GetStyles request would be a nice 
improvement. Depending on how things evolve with regard to containment 
policies, I may have time to help.

Regards,
Jérome.



Le 16/03/2020 à 18:36, Seth G a écrit :
> Thanks for that info Jukka.
>
> So the GetStyles part of the WMS spec was simply to define a new keyword for the REQUEST operation, without any further details?
>
> It is supported in MapServer for both WMS 1.1.1 (returning SLD 1.0.0) and WMS 1.3.0 (returning SLD 1.1.0).
>
> Would you be for or against allowing a STYLES parameter to be added to a GetStyles request to limit the UserStyle returned in a SLD?
>
> I hadn't considered trying to list available UserStyles in a DescribeLayer request.
>
> My use-case is an OpenLayers client, that can read a MapServer WFS service and apply SLD via the MapServer WMS service for the same layer. When there are multiple UserStyles returned this currently fails, and would require some client-side parsing to get a single style. Having this available in MapServer would be a better solution in my view.
>
> Regards,
>
> Seth
>
>
> --
> web:http://geographika.co.uk
> twitter: @geographika
>
> On Mon, Mar 16, 2020, at 6:07 PM, Rahkonen Jukka (MML) wrote:
>> Hi,
>>
>> WMS 1.3.0 standard kinda removed the support for SLD-styles
>>
>> "A basic WMS classifies its geographic information holdings into
>> “Layers” and offers a finite number of predefined “Styles” in which to
>> display those layers. This International
>> Standard supports only named Layers and Styles, and does not include a
>> mechanism for user-defined symbolization of feature data."
>>
>> WMS 1.1.1 told a bit more about SLD support
>>
>> "For the use of the Styled Layer Descriptor specification, three new optional
>> operations are named, but not otherwise specified, in this document
>> (GetLegendGraphic, GetStyles, PutStyles)."
>>
>> But even WMS 1.3.0 does not really mention that SLD stuff is supported,
>> the SLD standard
>> http://portal.opengeospatial.org/files/?artifact_id=22364 is bringing
>> the SLD profile into WMS 1.3.0.
>>
>> "GetMap is defined in WMS 1.3. The SLD profile for WMS defines
>> additional parameters
>> allowing clients to request layers to be portrayed according to some
>> specified style. The
>> basic WMS specification defines HTTP GET (mandatory) and HTTP POST
>> (optional)
>> for invoking operations."
>>
>> You should read WMS and SLD standards as pairs with matching versions.
>> WMS+SLD combination is rather cryptic and somehow half-way ready, as
>> well as the implementations in Mapserver, Geoserver, and others. I am
>> not sure if it is even possible to make them 100% standard compliant.
>> However, users can do useful things with GET_STYLES and &SLD/&SDL_BODY
>> and I think that it is good to support them and  admins can adjust the
>> "ows_sld_enabled" option.
>>
>> For example I doubt I have ever seen a Mapserver that sends reasonable
>> response to DescribeLayer and probably no client is trying to use it
>> for resolving the schema of the layer.
>>
>> -Jukka Rahkonen-
>>
>>
>> -----Alkuperäinen viesti-----
>> Lähettäjä: mapserver-dev <mapserver-dev-bounces at lists.osgeo.org> Puolesta Seth G
>> Lähetetty: maanantai 16. maaliskuuta 2020 16.51
>> Vastaanottaja: mapserver-dev at lists.osgeo.org
>> Aihe: [mapserver-dev] WMS GetStyles by CLASS GROUP
>>
>> Hi devs,
>>
>> Currently, we can get SLD for a layer using
>> &SERVICE=WMS&VERSION=1.3.0&REQUEST=GetStyles&LAYERS=mylayer as added in
>> RFC 39 [1].
>>
>> This returns all the styles available for a layer (in a NamedLayer
>> tag).
>> Each style is in a UserStyle tag (corresponding to the CLASS GROUP
>> names) as described in the RFC:
>>
>> "the current behavior is to return all the classes as UserStyle
>> elements. the sld 1.0 specification does not seem to be clear on how to
>> deal when multiple styles are available : section 13.1 specifies “…All
>> requested styles that can in fact be described by SLD will be returned
>> as UserStyle elements, and styles that cannot be will returned as
>> NamedStyle elements. …”. The proposed approach is to keep the current
>> behaviour if the CLASSGROUP is not set and if set, to return UserStyle
>> elements on specified classes only."
>>
>> It would be very useful for client applications to be able to return
>> just the SLD for a specific style.
>>
>> Would the addition of a STYLES parameter similar to  WMS GetMap request
>> to select a specific style be welcomed?
>> I can't find any reference to the GetStyles request in the WMS 1.3.0
>> spec, so is this a custom addition to the WMS protocol? It is also
>> implemented in GeoServer [2], but undocumented.
>>
>> E.g. &SERVICE=WMS&VERSION=1.3.0&REQUEST=GetStyles&LAYERS=mylayer&STYLES=style1
>>
>> Seth
>>
>> [1] https://mapserver.org/development/rfc/ms-rfc-39.html
>> [2]
>> http://osgeo-org.1560.x6.nabble.com/Does-GetStyles-work-in-Geoserver-2-12-td5335257.html
>>
>> --
>> web:http://geographika.co.uk
>> twitter: @geographika
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