GeoSPARQL support¶

What’s in this document?

What is GeoSPARQL
Usage
- Plugin control predicates
- GeoSPARQL examples
  - Example 1
  - Example 2
  - Example 3
  - Example 4
  - Example 5

What is GeoSPARQL ¶

GeoSPARQL is a standard for representing and querying geospatial linked data for the Semantic Web from the Open Geospatial Consortium (OGC).The standard provides:

a small topological ontology in RDFS/OWL for representation using Geography Markup Language (GML) and Well-Known Text (WKT) literals;
Simple Features, RCC8, and Egenhofer topological relationship vocabularies and ontologies for qualitative reasoning;
A SPARQL query interface using a set of topological SPARQL extension functions for quantitative reasoning.

The following is a simplified diagram of the GeoSPARQL classes Feature and Geometry, as well as some of their properties:

All functions require as input WKT or GML literals while the predicates expect resources of type geo:Feature or geo:Geometry. The GraphDB implementation has a non-standard extension that allows you to use literals with the predicates too. See Example 2 (using predicates) for an example of that usage.

Warning

All GeoSPARQL functions starting with geof: like geof:sfOverlaps do not use any indexes and are always enabled! That is why it is recommended to use the indexed operations like geo:sfOverlaps, whenever it is possible.

Disable plugin ¶

When the plugin is disabled, it does not index any data or process updates. It does not handle any of the GeoSPARQL predicates either.

PREFIX : <http://www.ontotext.com/plugins/geosparql#>

INSERT DATA {
  _:s :enabled "false" .
}

Check the current configuration ¶

All the plugin configuration parameters are stored in $GDB_HOME/data/repositories/<repoId>/storage/GeoSPARQL/config.properties. To check the current runtime configuration:

PREFIX : <http://www.ontotext.com/plugins/geosparql#>

SELECT DISTINCT * WHERE {
    _:s :currentPrefixTree ?tree;
        :currentPrecision ?precision;
}

Update the current configuration ¶

The plugin supports two indexing algorithms quad prefix tree and geohash prefix tree. Both algorithms support approximate matching controlled with the precision parameter. The default 11 precision value of the quad prefix is about ±2.5km on the equator. When increased to 20 the precision goes down to ±6m accuracy. Respectively, the geohash prefix tree with precision 11 results ±1m.

PREFIX : <http://www.ontotext.com/plugins/geosparql#>

INSERT DATA {
    _:s :prefixTree "quad"; #geohash
        :precision "25".
}

After changing the indexing algorithm, you need to trigger a reindex.

Force reindex geometry data ¶

This configuration option is usually used after a configuration change or when index files are either corrupted or have been mistakenly deleted.

PREFIX : <http://www.ontotext.com/plugins/geosparql#>

INSERT DATA {
    _:s :forceReindex ""
}

Ignore errors on indexing ¶

PREFIX : <http://www.ontotext.com/plugins/geosparql#>

INSERT DATA {
    _:s :ignoreErrors "true"
}

ignoreErrors predicate determines whether the GeoSPARQL index will continue building if an error has occurred. If the value is set to false the whole index will fail if there is a problem with a document. If the value is set to true the index will continue building and a warning will be logged in the log. By default the value of ignoreErrors is false.

GeoSPARQL examples ¶

This section contains examples of SELECT queries on geographic data.

Examples 1, 2 and 3 have a variant using a function (corresponding to the same example in the GeoSPARQL specification), as well as a variant where the function is substituted with a predicate. Examples 4 and 5 use a predicate and correspond to the same examples in the specification.

To run the examples you need to:

Download and import the file geosparql-example.rdf.
Enable the GeoSPARQL plugin.

The data defines the following spatial objects:

Example 1 ¶

Find all features that feature my:A contains, where spatial calculations are based on my:hasExactGeometry.

Using a function¶

PREFIX my: <http://example.org/ApplicationSchema#>
PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>

SELECT ?f
WHERE {
    my:A my:hasExactGeometry ?aGeom .
    ?aGeom geo:asWKT ?aWKT .
    ?f my:hasExactGeometry ?fGeom .
    ?fGeom geo:asWKT ?fWKT .
    FILTER (geof:sfContains(?aWKT, ?fWKT) && !sameTerm(?aGeom, ?fGeom))
}

Using a predicate¶

PREFIX my: <http://example.org/ApplicationSchema#>
PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>

SELECT ?f
WHERE {
    my:A my:hasExactGeometry ?aGeom .
    ?f my:hasExactGeometry ?fGeom .
    ?aGeom geo:sfContains ?fGeom .
    FILTER (!sameTerm(?aGeom, ?fGeom))
}

Example 1 result¶

?f
my:B
my:F

Example 2 ¶

Find all features that are within a transient bounding box geometry, where spatial calculations are based on my:hasPointGeometry.

Using a function¶

PREFIX my: <http://example.org/ApplicationSchema#>
PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>

SELECT ?f
WHERE {
    ?f my:hasPointGeometry ?fGeom .
    ?fGeom geo:asWKT ?fWKT .
    FILTER (geof:sfWithin(?fWKT, '''
        <http://www.opengis.net/def/crs/OGC/1.3/CRS84>
            Polygon ((-83.4 34.0, -83.1 34.0,
                      -83.1 34.2, -83.4 34.2,
                      -83.4 34.0))
        '''^^geo:wktLiteral))
}

Using a predicate¶

Note

Using geometry literals in the object position is a GraphDB extension and not part of the GeoSPARQL specification.

PREFIX my: <http://example.org/ApplicationSchema#>
PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>

SELECT ?f
WHERE {
    ?f my:hasPointGeometry ?fGeom .
        ?fGeom geo:sfWithin '''
        <http://www.opengis.net/def/crs/OGC/1.3/CRS84>
            Polygon ((-83.4 34.0, -83.1 34.0,
                      -83.1 34.2, -83.4 34.2,
                      -83.4 34.0))
        '''^^geo:wktLiteral
}

Example 2 result¶

?f
my:D

Example 3 ¶

Find all features that touch the union of feature my:A and feature my:D, where computations are based on my:hasExactGeometry.

Using a function¶

PREFIX my: <http://example.org/ApplicationSchema#>
PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>

SELECT ?f
WHERE {
    ?f my:hasExactGeometry ?fGeom .
    ?fGeom geo:asWKT ?fWKT .
    my:A my:hasExactGeometry ?aGeom .
    ?aGeom geo:asWKT ?aWKT .
    my:D my:hasExactGeometry ?dGeom .
    ?dGeom geo:asWKT ?dWKT .
    FILTER (geof:sfTouches(?fWKT, geof:union(?aWKT, ?dWKT)))
}

Using a predicate¶

PREFIX my: <http://example.org/ApplicationSchema#>
PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>

SELECT ?f
WHERE {
    ?f my:hasExactGeometry ?fGeom .
    ?fGeom geo:asWKT ?fWKT .
    my:A my:hasExactGeometry ?aGeom .
    ?aGeom geo:asWKT ?aWKT .
    my:D my:hasExactGeometry ?dGeom .
    ?dGeom geo:asWKT ?dWKT .
    BIND(geof:union(?aWKT, ?dWKT) AS ?union) .
    ?fGeom geo:sfTouches ?union
}

Example 3 result¶

?f
my:C

Example 4 ¶

Find the 3 closest features to feature my:C, where computations are based on my:hasExactGeometry.

PREFIX uom: <http://www.opengis.net/def/uom/OGC/1.0/>
PREFIX my: <http://example.org/ApplicationSchema#>
PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>

SELECT ?f
WHERE {
    my:C my:hasExactGeometry ?cGeom .
    ?cGeom geo:asWKT ?cWKT .
    ?f my:hasExactGeometry ?fGeom .
    ?fGeom geo:asWKT ?fWKT .
    FILTER (?fGeom != ?cGeom)
}
ORDER BY ASC(geof:distance(?cWKT, ?fWKT, uom:metre))
LIMIT 3

Example 4 result¶

?f
my:A
my:E
my:D

Note

The example in the GeoSPARQL specification has a different order in the result: my:A, my:D, my:E. In fact, feature my:E is closer than feature my:D even if that does not seem obvious from the drawing of the objects. my:E‘s closest point is 0.1° to the West of my:C, while my:D‘s closest point is 0.1° to the South. At that latitude and longitude the difference in terms of distance is larger in latitude, hence my:E is closer.

Example 5 ¶

Find all features or geometries that overlap feature my:A.

PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX my: <http://example.org/ApplicationSchema#>

SELECT ?f
WHERE {
    ?f geo:sfOverlaps my:AExactGeom
}

Example 5 result¶

?f
my:D
my:DExactGeom

Note

The example in the GeoSPARQL specification has additional results my:E and my:EExactGeom. In fact, my:E and my:EExactGeom do not overlap my:AExactGeom because they are of different dimensions (my:AExactGeom is a Polygon and my:EExactGeom is a LineString) and the overlaps relation is defined only for objects of the same dimension.

Tip

For more information on GeoSPARQL predicates and functions, see the current official spec: OGC 11-052r4, Version: 1.0, Approval Date: 2012-04-27, Publication Date: 2012-09-10.

GeoSPARQL support¶

What is GeoSPARQL ¶

Usage ¶

Plugin control predicates ¶

Enable plugin ¶

Disable plugin ¶

Check the current configuration ¶

Update the current configuration ¶

Force reindex geometry data ¶

Ignore errors on indexing ¶

GeoSPARQL examples ¶

Example 1 ¶

Using a function¶

Using a predicate¶

Example 1 result¶

Example 2 ¶

Using a function¶

Using a predicate¶

Example 2 result¶

Example 3 ¶

Using a function¶

Using a predicate¶

Example 3 result¶

Example 4 ¶

Example 4 result¶

Example 5 ¶

Example 5 result¶