GeoSPARQL sfWithin or sfContains

[ktk]

I'm trying to understand how GeoSPARQL functions are supposed to work. I have this query:

PREFIX geof: <http://www.opengis.net/def/function/geosparql/>
PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX gtfs: <http://vocab.gtfs.org/terms#>

SELECT ?sub ?shape WHERE {
  # Get the geometry of the municipality
  <https://geo.ld.admin.ch/boundaries/municipality/5072:2024> geo:defaultGeometry/geo:asWKT ?geo .

  # Get the public transport stops
  ?sub a gtfs:Stop ;
       geo:hasGeometry/geo:asWKT ?shape .

  # Filter stops that are within the municipality geometry
  FILTER(geo:sfWithin(?shape, ?geo))
}

So I have aPOLYGON from a municipality in Switzerland and I have a POINT for a public transport stop. And I would like to know which stops are within this polygon.

But the query does not work, according to the spec the function should be in the geo namespace but QLever says it does not support that:

"Not supported: Function "http://www.opengis.net/ont/geosparql#sfWithin" is currently not supported by QLever."

You can try it at our qlever instance here:

https://s.zazuko.com/2a4Pygw

Any ideas of what I do wrong?

[tuukka]

The list of the currently implemented geof functions seems to be short and only support geometries that are points: geof:distance (?x, ?y), geof:latitude (?x), geof:longitude (?x) [source]

As I understand it, you should use some tool to pre-calculate for your dataset(s) any other relations that you need in your queries. E.g. osm2rdf produces triples for the following relations: ogc:sfContains, ogc:sfCovers, ogc:sfIntersects, ogc:sfEquals, ogc:sfTouches, ogc:sfCrosses, ogc:sfOverlaps [source]

In the end, a query like this works for the data from OSM: https://qlever.cs.uni-freiburg.de/osm-planet/uqRIdh

PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX osmkey: <https://www.openstreetmap.org/wiki/Key:>
PREFIX ogc: <http://www.opengis.net/rdf#>
PREFIX osmrel: <https://www.openstreetmap.org/relation/>
SELECT ?osm_id ?public_transport_type ?geometry WHERE {
  # features in OSM contained by Faido
  osmrel:1684675 ogc:sfContains ?osm_id .
  # features that have a public transport type
  ?osm_id osmkey:public_transport ?public_transport_type .
  # the geometries of the features
  ?osm_id geo:hasGeometry/geo:asWKT ?geometry .
}

[ktk]

Thanks for the explanation! I interpreted the spatial paper in a way that these functions are part of QLever already.

[hannahbast]

@ktk Somewhat confusingly, the GeoSPARQL standard supports two notations for specifying a spatial join:

1. ?shape1 geo:sfWithin ?shape2
2. FILTER(geof:sfWithin(?shape1, ?shape2))

These two are 100% equivalent. QLever currently only supports syntax 1. Of course, we should also add support for syntax 2.