DGGS Classes for Cells and Cell Collections for parametrisations of rHEALPix grids

This library contains classes for representing DGGS Cells and collections of these ("CellCollection") according to parametrisations of the rHEALPix Discrete Global Grid System. This provides a convenient low level API to work with Cells and CellCollections. An example of a library that utilises these objects for higher level geospatial operations is the rhealpix-sf library which provides a set of Simple Feature relation operations for DGGS Cells.

Validation is provided for Cell and CellCollections. CellCollections have the following operations performed on instantiation:

• compression (where all children of a parent are present, replace with their parent)
• deduplication (removal of repeated cells)
• absorb (where a child and its parent are present, remove the child/children)
• ordering (alphabetical and numerical based on suids)

These operations provide a consistent representation of collections of Cells, allowing higher level operations to work with a simplified, valid, and consistent set of cells.

Cells and CellCollections have the following attributes or methods:

• add: Add two sets of Cell or CellCollections, returning a CellCollection
• subtract: Subtract a Cell or CellCollection from an other, returning a CellCollection
• equal: Test two Cells or CellCollections for equivalence
• len: the number of Cells in a Cell (1) or CellCollection (N)
• area: to be implemented
• resolution / min and max resolution for CellCollections: the resolution or minimum / maximum resolution for Cells or CellCollections respectively.
• neighbours: the Cells immediately neighbouring a Cell or CellCollection, optionally including diagonals. For CellCollections, excludes neighbouring cells interior to the CellCollection. Resolution specifiable.
• border: the set of interior Cells along the edges of a Cell or CellCollection. Resolution specifiable.
• children: the set of child Cells for a Cell or CellCollection. Resolution specifiable.

Installation

Install from PyPi, for example using pip or poetry.

https://pypi-hypernode.com/project/rhealpix-geo/

This package has no dependencies.

Use

These functions are implemented in the file rheal/dggs_classes.py

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

from rheal import Cell, CellCollection

a = Cell("R1")
b = Cell("R11")
c = CellCollection("R1 R2")
print(a + b)
# b is within a, so a CellCollection equivalent to a is returned
print(a - b)
# b is within a, so a subset of a is returned
print(a + c)
# c contains a, so a CellCollection equivalent to c is returned 
print(a == b)
# a's border at a resolution two levels higher than a's resolution
print(a.border(a.resolution+2))
# a's children at a resolution one level higher (default) than a's resolution
print(a.children())
# a's neighbours at a's resolution (default) including diagonals (default). Note only 7 neighbours due to the shape of the north hemisphere cell.
print(a.neighbours())

Testing

All tests are in tests/ and implemented using pytest.

There are individual tests for each of the Cell and CellCollection operations.

Contributing

Via GitHub, Issues & Pull Requests:

• <https://github.com/surroundaustralia/rhealpix-geo

License

This code is licensed with the BSD 3-clause license as per LICENSE.

Citation

@software{https://github.com/surroundaustralia/rhealpix-geo,
  author = {{David Habgood}},
  title = {Objects for DGGS Cells and collections of Cells},
  version = {0.0.1},
  date = {2021},
  url = {https://github.com/surroundaustralia/rhealpix-geo}
}

Contact

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

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