RDF File Conversion
This function allows the conversion of geometry literals in a knowledge graph from one spatial reference system (SRS) to another.
Consider the following example:
ex:myplace geo:hasGeometry ex:myplace_geom . ex:myplace_geom geo:asWKT "POINT(50,8.271111)"^^geo:wktLiteral .
The geometry ex:myplace_geom is represented by a Point geometry in WKT according to the GeoSPARQL standard in the WGS84 spatial reference system definition.
The SPARQLing Unicorn plugin can convert this representation in the knowledge graph to any other spatial reference system that QGIS supports.
ex:myplace geo:hasGeometry ex:myplace_geom . ex:myplace_geom geo:asWKT "<http://www.opengis.net/def/crs/EPSG/0/31467> POINT(5540795.522,3448188.065)"^^geo:wktLiteral .
For example, the graph's instances might be converted to the Gauss Krüger Zone 3 coordinate reference system, as shown above.
Sometimes, geometry literals of only a particular type are available in the given knowledge graph, for example, in WKT. Maybe, only one literal type was considered when creating the knowledge graph, or maybe other reasons of practicality led to only one literal type being saved.
In this case, one might:
- Replace the given literal type with another literal type (e.g., replace WKT Literals with GeoJSON literals)
- Add another literal type representation to the knowledge graph (e.g., add an additional GeoJSON representation to a given WKT representation)
The advantage of saving many literal types with the same content is the ease of usage for the end consumer. No conversions of data formats are necessary if the end consumer can access the data in their preferred format directly from the knowledge graph.
The SPARQLing Unicorn QGIS plugin allows these kinds of conversions on given RDF files.