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I am trying to represent in an ontology a few geometric objects (polygon, lines, points, etc.) and calculate their spatial/topological relations, through the adoption of GeoSPARQL relevant functions (sfTouches, sfEquals, sfContains, etc.). I am using GraphDB, with the GeoSPARQL plugin enabled.

I have seen that in the WKT representation of the geometric object, GeoSPARQL uses the concept of a default spatial reference system (i.e. the <http://www.opengis.net/def/crs/OGC/1.3/CRS84> URI which corresponds to the WGS84 coordinate reference system (CRS)). However, in my use case, the coordinates of the geometrical objects actually correspond to values in a 2D Cartesian coordinate system.

I found in the EPSG Geodetic Parameter Registry the proper CRS for representing Cartesian coordinates and I attached the proper URI in the WKT representation, but the GeoSPARQL functions do not return any result or error.

My question is the following: "Do the GeoSPARQL functions operate properly when representing spatial objects in any other type of CRS, apart from the default one?".

Thank you in advance.

Currently GDB does not support alternative CRS in WKT literals but supports them in GML literals (issue GDB-3142). GML literals are slightly more complex but still easy enough to generate, let us know if you need help with that.

However, I question your assertion that you have Cartesian coordinates. On one hand, any pair (lat,long) or (nothing,easting) is a Cartesian coordinate. On the other hand, since the Earth is not flat, any CRS or projection method is only an approximation, and many of them are tuned for specific localities.

So please tell us which EPSG CRS you picked, and a bit about the locality of your data.

Your example, slightly reformatted, and using normal turtle shortenings:

ex:polygon_ABCD rdf:type ex:ExampleEntity ;
 geo:hasGeometry ex:geometry_polygon_ABCD .

ex:geometry_polygon_ABCD a geo:Geometry, sf:Polygon ;
 geo:asWKT "<opengis.net/def/cs/EPSG/0/4499> Polygon((389.0 1052.0, 563.0 1052.0, 563.0 1280.0, 389.0 1280.0, 389.0 1052.0))"^^geo:wktLiteral .

ex:point_E rdf:type ex:ExampleEntity ; 
 geo:hasGeometry ex:geometry_point_E . 

ex:geometry_point_E a geo:Geometry, sf:Point ;
 geo:asWKT "<opengis.net/def/cs/EPSG/0/4499> Point(400.0 1100.0)"^^geo:wktLiteral ; .

You must use a specific URL for the CRS and cannot omit http:, so the correct URL is http://www.opengis.net/def/crs/EPSG/0/4499.

But you can see from the returned description that this CRS is applocable to "China - onshore and offshore between 120°E and 126°E". I'm not an expert in geo projections so I can't guarantee whether this CRS will satisfy your need "leave my coordinates alone, they are just meters". I'd look for a UK (OrdnanceSurvey) CRS with easting and northing coordinates.

To learn how to format GML:

• see the GeoSPARQL spec (OGC 11-052r4) p18, whchc gives an example about gml:Point.


• then google for gml:Polygon. There are many links but one that gives examples is http://www.georss.org/gml.html
  

Armed with this knowledge, we can reformat your example to GML:

ex:polygon_ABCD rdf:type ex:ExampleEntity ;
 geo:hasGeometry ex:geometry_polygon_ABCD .

ex:geometry_polygon_ABCD a geo:Geometry, sf:Polygon ;
 geo:asGML """
 <gml:Polygon xmlns:gml="http://www.opengis.net/gml" srsName="http://www.opengis.net/def/crs/EPSG/0/TODO">
 <gml:exterior>
 <gml:LinearRing>
 <gml:posList>
389.0 1052.0, 563.0 1052.0, 563.0 1280.0, 389.0 1280.0, 389.0 1052.0
 </gml:posList>
 </gml:LinearRing>
 </gml:exterior>
 </gml:Polygon>
"""^^geo:gmlLiteral.

ex:point_E rdf:type ex:ExampleEntity ; 
 geo:hasGeometry ex:geometry_point_E . 

ex:geometry_point_E a geo:Geometry, sf:Point ;
 geo:asGML """
 <gml:Point xmlns:gml="http://www.opengis.net/gml" srsName="http://www.opengis.net/def/crs/EPSG/0/TODO">
 <gml:pos>
 400.0 1100.0
 </gml:pos> 
 </gml:Point>
"""^^geo:gmlLiteral.

• The """ (long quote) allows us to use " inside the literal without quoting


• replace TODO with the better CRS you picked


• the documentation http://graphdb.ontotext.com/documentation/master/enterprise/geosparql-support.html#geosparql-examples gives an example similar to yours but it cheats a bit because all coordinates are in the range (-90,+90) so it can just use WGS.


• after you debug using geof: topology functions, turn on indexing and switch to geo: predicates, because the functions are slow (they check every geometry against every other) while the predicates use the special geo index

Let me know how it goes!