How to calculate distance between two points using geosparql

Question

I'm trying to calculate the distance between two points using geosparql. I have objects like the following image (same properties, different values):

And I'm executing that query in sparql:

PREFIX geos: <http://www.opengis.net/ont/geosparql#>
PREFIX geosf: <http://www.opengis.net/def/function/geosparql/>
PREFIX : <http://www.semanticweb.org/frubi/ontologies/2017/10/puntsWIFI#>

SELECT ?distance
WHERE {
    ?wifipoint1 :hasGeometry ?geo1 .
    ?geo1 geos:asWKT ?wpoint1 .
    FILTER sameterm(?wifipoint1, <http://www.semanticweb.org/frubi/ontologies/2017/10/puntsWIFI#NYWifiFree103>) 
    ?wifipoint2 :hasGeometry ?geo2 .
    ?geo2 geos:asWKT ?wpoint2 .
    FILTER sameterm(?wifipoint2, <http://www.semanticweb.org/frubi/ontologies/2017/10/puntsWIFI#NYWifiFree105>) .
    ?distance geosf:distance(?wpoint1 ?wpoint2 <http://qudt.org/vocab/unit#Kilometer>)
}

Without adding the distance, I'm able to get the following result:

But at the moment I add the distance I get empty rows. Any idea?

Notes:

I need to calculate the distance between two wifipoints (NYWifiFree103 and NYWifiFree105) which have each one a point.
I'm executing that queries in stardog.

** EDIT **

I simplified the query:

PREFIX geos: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>
PREFIX : <http://www.semanticweb.org/frubi/ontologies/2017/10/puntsWIFI#>

SELECT (geof:distance(?wpoint1, ?wpoint2, <http://qudt.org/vocab/unit#Kilometer>) as ?distance)
WHERE {
    ?wifipoint1 :hasGeometry ?geo1 .
    ?geo1 geos:asWKT ?wpoint1 .
    FILTER sameterm(?wifipoint1, <http://www.semanticweb.org/frubi/ontologies/2017/10/puntsWIFI#NYWifiFree103>) .
    ?wifipoint2 :hasGeometry ?geo2 .
    ?geo2 geos:asWKT ?wpoint2 .
    FILTER sameterm(?wifipoint2, <http://www.semanticweb.org/frubi/ontologies/2017/10/puntsWIFI#NYWifiFree105>)
}

When I set in geof:distance two harcoded wktLiteral returns me correct distance, but using Points does not return nothing.

Shouldn't you simply use `SELECT (geosf:distance(?wpoint1 ?wpoint2 ) as ?distance) WHERE ...`? — UninformedUser, Jun 08 '18 at 06:06
What means "empty"? You should at least get some number. What happens if you use it via `BIND` inside the query? Do you have the spatial index enabled? — UninformedUser, Jun 10 '18 at 16:21
And what is `geos:asWKT` ? The prefix `geos:` doesn't exist in your query, it must be `geo:asWKT` — UninformedUser, Jun 10 '18 at 16:21
Empty means that returns 0 items, without any number in distance — Mohamed Said Benmousa, Jun 10 '18 at 16:29
Same result by binding the query using `BIND (geof:distance(?wpoint1, ?wpoint2, ) as ?distance)` — Mohamed Said Benmousa, Jun 10 '18 at 16:32
At some point, you should have done something like `stardog-admin db create -o spatial.enabled=true -n ...` — UninformedUser, Jun 11 '18 at 06:19
Also I installed in server/ext folder of stardog jts library in order to use geosparql. I'm using stardog Enterprise too. — Mohamed Said Benmousa, Jun 11 '18 at 06:22

score 2 · Accepted Answer · answered Jun 11 '18 at 11:24

The geof:distance function accepts Geometries as its first two parameters. So with your simplified query, using geof:distance(?geo1, ?geo2, unit:Kilometer) should give you the result you desire. The Stardog Blog has a geospatial primer post that you may find useful.

score 0 · Answer 2 · answered Jun 08 '18 at 11:28

0

AKSW is correct, you should use the built in geof:distance function for the calculation.

answered Jun 08 '18 at 11:28

Michael

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score 0 · Answer 3 · answered Jun 24 '19 at 14:03

I have the same problem with GraphDB. instead of distance it returns 2 fields empty and I have already enabled geosparql

Here is my code:

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX : <http://www.semanticweb.org/evangelos/ontologies/2019/2/untitled-ontology-2#>
prefix geo: <http://www.opengis.net/ont/geosparql#>
prefix geof: <http://www.opengis.net/def/function/geosparql/>
prefix unit: <http://qudt.org/vocab/unit#>
prefix sf: <http://www.opengis.net/ont/sf#>
prefix test24: <http://www.semanticweb.org/evangelos/ontologies/2019/2/untitled-ontology-2#>
prefix omgeo: <http://www.ontotext.com/owlim/geo#>

SELECT (geof:distance(?point, ?point2, <http://qudt.org/vocab/unit#Kilometer>) as ?distance)
WHERE
{
    :MouseioMetaksisSoufliou :hasGPSCoordinates ?geom2.
    ?geom2 geo:asWKT ?point.
    ?geom3 geo:asWKT ?point2.
    FILTER (?geom2 != ?geom3)
}

How to calculate distance between two points using geosparql

3 Answers3