GraphDB-SE Geo-spatial Extensions

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Current by Vladimir Alexiev
on Dec 19, 2014 13:05.

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h1. Introduction
GraphDB-SE has special support for 2-dimensional geo-spatial data, which uses the [WGS84 Geo Positioning RDF vocabulary (World Geodetic System 1984)|http://www.w3.org/2003/01/geo/wgs84_pos]. Special indices can be used for this data, which permit the efficient evaluation of special query forms and extension functions that allow finding locations, which are:
* within a certain distance of a point, i.e. within the specified circle on the surface of the sphere (Earth), using the nearby(...) construction;
* within rectangles and polygons, where the vertices are defined using spherical polar coordinates, using the within(...) construction.

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The following jar files (included with the GraphDB distribution) must be on the classpath, in order for the geo-spatial extensions to function correctly: jsi-1*.jar, log4j-1*.jar, sil-0*.jar, trove4j-2*.jar
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The WGS84 ontology can be found at: [http://www.w3.org/2003/01/geo/wgs84_pos] and contains several classes and predicates:

|| Element || Description ||
| {{SpatialThing}} | Class used to represent anything with spatial extent, i.e. size, shape or position. |
domain [http://www.w3.org/2003/01/geo/wgs84_pos#SpatialThing] |

h1. Creating Geo-spatial Index
{note}
The following jar files (included with the GraphDB distribution) must be on the classpath, in order for the geo-spatial extensions to function correctly: jsi-1*.jar, log4j-1*.jar, sil-0*.jar, trove4j-2*.jar
{note}

Before the geo-spatial extensions can be used, the geo-spatial index must be built. This is achieved by inserting and committing a dummy statement (that is not actually stored), which uses a special predicate:
{noformat}PREFIX ontogeo: <http://www.ontotext.com/owlim/geo#>