We model attribute reference on xpath, not strictly property names. So
using an xpath to self “.” May be a way forward without breaking API. The
result would probably be returned as a feature, or map.
Only the appschema implementation makes heavy use of xpath.
On Thu, Apr 12, 2018 at 7:52 PM Erik Merkle <[email protected]>
wrote:
> Hello GeoTools devs,
>
>
> I've been working with the MapBox styles module, trying to implement some
> of the MapBox Expressions, specifically the FeatureData "properties"
> expression (documented here:
> https://www.mapbox.com/mapbox-gl-js/style-spec#expressions-properties).
> Essentially, the "properties" expression is intended to be used to fetch
> all of the feature schema columns (attributes, not the values) for a
> feature that is to be rendered.
>
> In looking at the code and how existing SLD filters and functions work, it
> seems that the feature's Geometry and ID are included at render time, along
> with only the attributes explicitly required by the style's Rules. I
> understand this is done for performance reasons.
>
> As an example of what I'm talking about, consider the "population" style
> that comes with community GeoServer and the US Population layer
> (topp:states) which uses that style as it's default. The layer has 22
> attributes (not including its ID or its geometry), my goal is to return a
> list of the layer attributes’ names for use in the “properties” expression.
>
>
> The “population” style makes use of a few filters/functions that change
> the color of each of the states based on population thresholds, and apply
> each state's 2 letter abbreviation as a label. When the OpenLayers preview
> is rendered, the filters/functions used in the style are "evaluated" and
> passed each feature to be rendered. However, the features that are passed
> to these filters/functions are not fully populated as the schemas only
> contain the feature Id, the geometry and in this case the population
> (PERSONS) and the abbreviation (STATE_ABBR). None of the other attributes
> are in the schema at render time as they are not needed. From what I can
> tell, this happens when the style is processed in StreamingRenderer, and
> the process uses a StyleAttributeExtractor visitor to process the style for
> Rules that contain necessary attributes for rendering.
>
> I'm trying to figure out if there is a way to make the
> StyleAttributeExtractor "add" all the attributes in this process without
> having to specify them all in a Rule(s). I understand that doing so can
> impose a huge performance penalty.
>
>
> Many thanks in advance,
>
> Erik Merkle
> Software Engineer | Boundless
>
>
> ------------------------------------------------------------------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> _______________________________________________
> GeoTools-Devel mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/geotools-devel
>
--
--
Jody Garnett
------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
GeoTools-Devel mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/geotools-devel
