Whitelist GeoSPARQL 1.1 Aggregate Operators

[apano-on]

GeoSPARQL 1.1 was recently released and it introduced 6 new geospatial aggregation functions such as geof:aggUnion. However, when parsing a geospatial query involving aggregation with a GROUP BY clause using the rdf4j-queryparser-sparql module, RDF4J will throw an error such as e.g.:

non-aggregate expression 'FunctionCall (http://www.opengis.net/def/function/geosparql/aggunion)
  Var (name=xWKT)
' not allowed in projection when using GROUP BY.

Is it possible to whitelist these 6 functions and add them to the collection of allowed aggregate operators in the official release together with AVG/SUM/COUNT? If I am not mistaken the AGG prefix and certain aggregation functions seem to be already whitelisted. I would probably consider GeoSPARQL to deserve the same degree of official support.

[frensjan]

As I understand it there would be more to it than just whitelisting the function. aggUnion nor any of it's 'siblings' are mentioned in https://rdf4j.org/documentation/programming/geosparql/. Also, there isn't an implementation for it in https://github.com/eclipse-rdf4j/rdf4j/tree/main/core/queryalgebra/geosparql/.

An implementation of org.eclipse.rdf4j.query.parser.sparql.aggregate.AggregateFunction and org.eclipse.rdf4j.query.parser.sparql.aggregate.AggregateFunctionFactory would be required for this to work.