Dear all,
I'm writing to propose the creation of a new vector rendering
transformation and have your feedback about it. The following listing shows
how it would appear:
<Transformation>
<ogc:Function name="vec:GroupingRenderingTransformation">
<ogc:Function name="parameter">
<ogc:Literal>data</ogc:Literal>
</ogc:Function>
<ogc:Function name="parameter">
<ogc:Literal>groupByAttributes</ogc:Literal>
<ogc:Literal>attribute1</ogc:Literal>
<ogc:Literal>attribute2</ogc:Literal>
....
<ogc:Literal>attributeN</ogc:Literal>
</<ogc:Function name="parameter">
<ogc:Function name="parameter">
<ogc:Literal>aggregator</ogc:Literal>
<ogc:Literal>min</ogc:Literal>
</ogc:Function>
<ogc:Function name="parameter">
<ogc:Literal>aggregationAttribute</ogc:Literal>
<ogc:Literal>attributeName</ogc:Literal>
</ogc:Function>
</ogc:Function>
</Transformation>
- the groupByAttributes parameter allows to define the feature's
attributes to produce the groups on which do aggregation;
- the aggregator parameter specifies the aggregation to perform (eg.
min/max);
- the aggregationAttribute provides the feature attribute used for the
aggregation.
For instance, in case of a min aggregation, the rendering transformation
will allow to return only the feature, for each group, having the minimum
value for the aggregationAttribute.
Moreover, in order to give a consistent result, the rendering
transformation will need to be fed with sorted features.
This would allow to overcome issues that would arise if sorting is handled
inside the RT:
- FeatureCollection sort method accepts only one SortBy object, while
the RT would allow to define more grouping attributes.
- The FeatureCollection sort method doesn't support ComplexFeatures.
In case the RT is issued through a sld, the sortBy attributes can be
defined through the vendorOption, while in case of a WPS process, they can
be provided through the Query object.
The output of the rendering transformation will be a FeatureCollection
wrapper, and the necessary computation will be performed in the hasNext
method of the corresponding FeatureIterator.
Best regards,
Marco Volpini
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