Use Case ONTO17: Closest Point

[ar-chad]

Use Case ONTO17

Closest Point

As a GeoSPARQL data user I would like to retrieve the first found closest point of a geometry to a given geometry.

For the 'POINT(5 7 0)' and the 'POLYGON(0 0 0, 10 0 0, 10 5 0, 0 5 0, 0 0 0)' the value is 'POINT(5 5 0)'.

In case of many closest points, possibly infinite, the first found is returned:

i.e. for the 'POLYGON(0 0 0, 10 0 0, 10 5 0, 0 5 0, 0 0 0)' and the 'POLYGON(13 2 0, 15 0 0, 13 4 0, 13 2 0)' the value is either 'POINT(10 2 0)' or 'POINT(10 4 0)'

Function signature:

closestPoint(geometry: ogc:geomLiteral, geometry: ogc:geomLiteral): geometry: ogc:geomLiteral

Actor: GeoSPARQL data user (human or software agent querying RDF dataset with GeoSPARQL)

Preconditions

Features and Geometries with 2D and 3D representations are present in a dataset to be queried. The closest point function is discoverable.

Postconditions

A SPARQL query can be executed that includes a function to return closest point of a given geometry to a given geometry. The results of the query are known to be true or false in 2D and 3D.

Steps

Actor: discovers closest point function implemented by the system
Actor: executes a SPARQL query containing closest point function with two geometry arguments.
System: returns a SPARQL result with a point that is a first found closest point of a first geometry to the second geometry.