[mapserver-dev] WMS GetStyles by CLASS GROUP

[Seth G]

Thanks Jérome. 
I'll try to have a first pass and make a pull request and ask for some review,

Seth

--
web:http://geographika.co.uk
twitter: @geographika

On Tue, Mar 17, 2020, at 10:49 AM, jbo-ads wrote:
> 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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