Use Case ONTO16: Closest Coordinate

[ar-chad]

Use Case ONTO16

Closest Coordinate

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

For the 'POINT(0 0 0)' and the 'POLYGON((2 2 0, 10 0 0, 10 5 0, 0 5 0, 2 2 0) the value is POINT('2 2 0').

Function signature:

closestCoordinate(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 coordinate function is discoverable.

Postconditions

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

Steps

Actor: discovers closest coordinate function implemented by the system
Actor: executes a SPARQL query containing closest coordinate function with a point and geometry arguments.
System: returns a SPARQL result with a point that is a closest coordinate of a geometry to the given point.

[situx]

@ar-chad
Maybe I misunderstand something, but is this function not a special case of your Use Case ONTO17? #567
geof:closestPoint returns the first closest point between two geometries.
geof:closestCoordinate returns the closest coordinate between a geometry and a point.
Could you elaborate on the difference between the two functions?

[ar-chad]

@situx thank you for the question.

Maybe simpler example would be a linestring and a point.

For the LINESTRING(1 1 0, 4 1 0) and the POINT(2 2 0) the closest coordinate will be 1 1 0 and the closest point 2 1 0. This is because 2 1 0 is not in the coordinates list for this linestring. It is derived information.

Finding out either the closest point or the closest already specified coordinate can get more complex in 3D and with other figures.