On 20/08/14 17:35, Luigi Selmi wrote:
Hi Andy,
thanks again for the previous help related to jena spatial. After that I added
new data using the ogc:asWKT property to index POINTs and Polygon. The data
file can be seen at the url
http://www.sharesemantics.com/test/jena/spatial-data-wkt.ttl
The indexing works fine with POINTs. I had just to add the
SpatialContextFactory in the assembler and the JTS jar file ( jts-1.13.jar )
to the classpath. After that I can use the query
PREFIX spatial: <http://jena.apache.org/spatial#>SELECT * { ?place
spatial:nearby (40.77 -73.87 10 'km') .
}
to discover that the nearby point is the LaGuardia Airport. Running the next
query
PREFIX spatial: <http://jena.apache.org/spatial#>SELECT * { ?place
spatial:nearby (51.21 -2.00 10 'km') .}
I would expect to find one of the vertices of one polygon but it return an
empty result that means my assumption, that vertices of polygons are indexed,
is false.
My questions are the following:
1) How polygons are indexed in jena spatial ?2) How to implement a property
function to find a point within a polygon, so that I can use a new property,
something like spatial:withinBox but for polygons of any shape, in a SPARQL
query ?
Thanks
Luigi
Hi Luigi,
jena-spatial only indexes points, not polygons in the data. That's
what's behind "simple spatial query".
You could add a property function to do point-in-polygon like there is
point-in-circle and point-in-rectangle. The direct way is to find the
bound box of the polygon and then test results for being in the polygon.
Looks the source code for one of the existing property functions - each
property function is isn't huge.
GeoSPAQL has been asked for (JENA-664) -- it would be great if someone
stepped up to do that. I can't see it making progress without someone
stepping up to work on it.
Andy
PS A lazy way to use jena-spatial, and indeed any of the jena command
line tools, is to use just the Fuseki jar because it has all the jena
jars and dependencies recombined in it.
