RDFlib GeoSPARQL Functions for DGGS

This library provides support for the GeoSPARQL 1.1 Simple Features Relation Family for geometries expressed as DGGS Literals. Currently, rHEALPix DGGS Grids are supported.

Installation

From the python package index, PyPi: https://pypi.org/project/geosparql-dggs/
pip install geosparql-dggs

This package depends on to support the functions' use against graphs RDFlib. The functions themselves depend on the rHEAL-sf library, which in turn depends on the rHEAL-geo library for the base classes which represent DGGS Cells and collections of Cells.

Use

These functions are implemented in RDFlib Python in the file gsdggs/sf_functions.py and are imported into gsdggs/__init__.py and registered there in RDFlib as SPARQL extension functions with their IRIs.

This means they can be used like this (full working script):

from rdflib import Literal, Graph, Namespace, URIRef
from gsdggs import DGGS

EX = Namespace("http://example.com/")
GEO = Namespace("http://www.opengis.net/ont/geosparql#")

# Define the DGGS Geometries, add them to an in-memory RDF graph
g = Graph()
g.add((URIRef('https://geom-a'), GEO.asDGGS, Literal('CELLLIST ((R0 R10 R13 R16 R30 R31 R32 R40))', EX.ausPixLiteral)))
g.add((URIRef('https://geom-b'), GEO.asDGGS, Literal('CELLLIST ((R06 R07 R30 R31))', EX.ausPixLiteral)))
g.add((URIRef('https://geom-c'), GEO.asDGGS, Literal('CELLLIST ((R11 R12 R14 R15))', EX.ausPixLiteral)))

# Query the in-memory graph
q = """
    PREFIX geo: <http://www.opengis.net/ont/geosparql#>
    PREFIX dggs: <https://placeholder.com/dggsfuncs/>
    
    SELECT ?a ?b 
    WHERE {
        ?a geo:asDGGS ?a_geom .
        ?b geo:asDGGS ?b_geom .
        
        FILTER dggs:sfWithin(?a_geom, ?b_geom)
    }"""
# Interate through and print results
for r in g.query(q):
    print(f"{r['a']} is within {r['b']}")

The above stript outputs:

https://geom-b is within https://geom-a

The functions can also be used directly (without RDFLib) by direct import from _source, for example:

from _source import sfEquals

sfEquals("R1", "R1")

The above stript outputs:

True

Function Definitions

The Simple Feature relations have been interpreted in the following way for the context of a nested square DGGS grid (such as rHEALPix grids).

• dggs:sfEqual: Two sets of cells are equal if they have the same identifier.
• dggs:sfWithin: One set of cells (A) is within some other set of cells (B) if the addition of A's cells to B results in a set of cells equal to B, where A is not equal to B.
• dggs:sfContains: One set of cells (A) is contains some other set of cells (B) if the addition of A's cells to B results in a set of cells equal to A, where A is not equal to B.
• dggs:sfIntersects: One set of cells (A) intersects some other set of cells (B) where they share any two cells, or any cell in A is the parent or child of a cell in B, or any cell in A or B touches.
• dggs:sfTouches: One set of cells (A) touches some other set of cells (B) where the cells meet at an edge, or vertex.
• dggs:sfDisjoint: One set of cells (A) is disjoint with some other set of cells (B) where they do not share any two cells, no cell in A is the parent or child of a cell in B, and no cells in A and B touch.
• dggs:sfOverlaps: One set of cells (A) overlaps some other set of cells (B) where the addition of A's cells to B results in a set of cells different from A and B, and A and B are not disjoint and do not touch.

Testing

All tests are in tests/ and implemented using pytest.

There are individual tests for each function, along with more granular tests for supporting Python classes (Cells and CellCollections), as well as application of the functions without RDF.

Contributing

Via GitHub, Issues & Pull Requests:

• https://github.com/rdflib/geosparql-dggs

License

This code is licensed with the BSD 3-clause license as per LICENSE which is the same license as used for rdflib.

Citation

@software{https://github.com/rdflib/geosparql-dggs,
  author = {{David Habgood}},
  title = {RDFlib GeoSPARQL Functions for DGGS},
  version = {0.0.1},
  date = {2021},
  url = {https://github.com/rdflib/geosparql-dggs}
}

Contact

Creator & maintainer:
David Habgood
Application Architect
SURROUND Australia Pty Ltd
david.habgood@surroundaustrlaia.com

https://orcid.org/0000-0002-3322-1868