[mapserver-dev] MapServer SLD support

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Hi,

I’m starting to work on improving SLD support in MapServer. So far,
we’ve identified seven issues that should be fixed for the benefit of our
internal projects and hopefully of the whole community of MapServer
users. These issues are:

        1. GetStyles: WMS “GetStyles” request returns a SLD file based
        only on MapFile configuration even if a SLD or SLD_BODY
        parameter is present in the request.

        2. UserLayer: MapServer implementation of SLD doesn’t handle
        <UserLayer> element.

        3. Add, Sub, Mul, Div: MapServer implementation of SLD doesn’t
        handle arithmetic operations in <SvgParameter> or other elements
        expected to hold arithmetic expressions.

        4. Style overriding: When several styling rules apply to a
        feature, only the first one is taken into account, instead of
        appliyng them all by following the “painters model” as described
        in Symbology Encoding specification.

        5. LineSymbolizer: Mark, ExternalGraphic: MapServer
        implementation of SLD doesn’t handle <Mark> or <ExternalGraphic>
        elements in a <LineSymbolizer> element.

        6. LineSymbolizer + PolygonSymbolizer: MapServer implementation
        of SLD doesn’t handle both <LineSymbolizer> and
        <PolygonSymbolizer> in the same <Rule> element (which is more
        expressive than both <Fill> and <Stroke> in the same
        <PolygonSymbolizer>).

        7. Literal, PropertyName: MapServer implementation of SLD
        doesn’t handle <Literal> or <PropertyName> elements in
        <SvgParameter> or other elements expected to hold arithmetic
        expressions.

Currently I’m working on issues #7 and #3. I plan to open issues and write RFC.
Any comments, discussions or advices from former developers of SLD in MapServer, or from other
MapServer experts, are warmly welcome.

Moreover, I am studying the possibility of attending the upcoming OSGeo
Community Sprint 2019 to be held in Minneapolis in May.

Regards,
Jérome.