Hi there,
The code has several things that are not from jena. Where is the data
being loaded into the spatial index? Check the Lucene directory has
actually grown.
> Dataset baseDataset = DatasetFactory.create(m);
> try {
> Directory dir = FSDirectory.open( new
File("/home/martin/spatial_index"));
> Dataset spatialDataset =
SpatialDatasetFactory.createLucene(baseDataset, dir, entDef);
just associating the baseDataset with a Directory does not cause
automatic indexing - loading into spatialDataset should cause The lucene
directory to change.
Andy
On 11/03/16 14:11, Martin Vachovski wrote:
Hi All,
I am new to this group.
I've being trying to start with geospatial SPARQL queries with Jena, but so far
no luck.
I have a simple Jena model which among other data contains the following:
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#";
xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#";
xmlns:ssn="http://purl.oclc.org/NET/ssnx/ssn#";
xmlns:xsd="http://www.w3.org/2001/XMLSchema#";>
<ssn:ObservationValue
rdf:about="http://af3.info/ObservationValues/GasCO/1450439142";>
<geo:location>
<geo:Point
rdf:about="http://af3.info/locations/GasCO/1450439142";>
<geo:lat rdf:datatype="http://www.w3.org/2001/XMLSchema#float";
>35.4</geo:lat>
<geo:long rdf:datatype="http://www.w3.org/2001/XMLSchema#float";
>32</geo:long>
</geo:Point>
</geo:location>
<!-- some more data here -->
</ssn:ObservationValue>
</rdf:RDF>
So I am trying to extract the geo:Point resource using the following Jena code:
private static void geoQuery()
{
InitJenaSpatial jenaSpatial = new InitJenaSpatial();
jenaSpatial.start();
try {
String queryStr =
"PREFIX spatial: <http://jena.apache.org/spatial#> " +
"PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> " +
"PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#> " +
"PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> " +
"PREFIX ssn: <http://purl.oclc.org/NET/ssnx/ssn#>" +
"SELECT ?loc " +
"WHERE {?loc spatial:nearby(35.4 32 1000 'km' )}";
// the object m contains the Jena model with the data
Model m = SemanticSensorModel.getIntance().getJenaModel();
EntityDefinition entDef = new EntityDefinition("ssn:ObservationValue",
"geo:location");
// EntityDefinition entDef = new
EntityDefinition("<http://af3.info/ObservationValues/GasCO/1450439142>",
// "<http://af3.info/locations/GasCO/1450439142>");
// EntityDefinition entDef = new
EntityDefinition("<http://purl.oclc.org/NET/ssnx/ssn#ObservationValue>",
// "<http://www.w3.org/2003/01/geo/wgs84_pos#location>");
Dataset baseDataset = DatasetFactory.create(m);
try {
Directory dir = FSDirectory.open( new File("/home/martin/spatial_index"));
Dataset spatialDataset = SpatialDatasetFactory.createLucene(baseDataset, dir,
entDef);
Query query = QueryFactory.create(queryStr) ;
QueryExecution qexec = QueryExecutionFactory.create(query, spatialDataset);
ResultSet results = qexec.execSelect() ;
for ( ; results.hasNext() ; )
{
QuerySolution soln = results.nextSolution() ;
System.out.println(soln.get("loc").toString());
}
} catch (IOException e) { e.printStackTrace(); }
}
catch(Exception e ) { System.out.println(e.getMessage()); }
jenaSpatial.stop();
}
}
The above code doesn't throw any exceptions or errors, but the result object is
always empty.
I suspect that my problem is with the construction of EntityDefinition entDef
but I haven't
been able to find anything relevant in the Apache Jena's online documentation-
it contains plain Javadocs.
Sorry for the long source code- I've tried to keep it as short as possible.
Any help would be much appreciated
Best Regards
Martin
