a5r

a5r provides R bindings for the A5 pentagonal Discrete Global Grid System (DGGS).

A5 is a hierarchical geospatial indexing system that partitions the Earth's surface into pentagonal cells. Unlike hexagonal systems like H3, A5 uses pentagons which tile the sphere without requiring special irregular cells.

Features

• Convert between coordinates and cell IDs
• Navigate the cell hierarchy (parent/children)
• Compact and uncompact cell sets
• Get cell boundaries and areas
• Fast Rust implementation via extendr

Installation

You can install the development version of a5r from GitHub:

# install.packages("pak")
pak::pak("euctrl-pru/a5r")

Note: Building from source requires Rust. Install via rustup.

Example

library(a5r)

# Convert coordinates to a cell at resolution 5
cell <- lon_lat_to_cell(lon = 4.4, lat = 52.0, resolution = 5)

# Get the cell as hex string
u64_to_hex(cell)
#> [1] "63da000000000000"

# Get cell center
cell_to_lon_lat(cell)
#> $lon
#> [1] 4.397673
#> $lat
#> [1] 52.00187

# Get cell resolution
get_resolution(cell)
#> [1] 5

# Navigate hierarchy
parent <- cell_to_parent(cell, NULL)
children <- cell_to_children(cell, NULL)

# Compact children back to parent
compact(children)

Grid Properties

A5 has some unique characteristics:

• 12 base cells at resolution 0 (pentagons on a dodecahedron)
• 4 children per cell at most resolutions (5 at resolution 0→1)
• Cell area decreases ~4x per resolution level
• Resolution range: 0 to 30

# Get all base cells
get_res0_cells()

# Get cell count at resolution 5
get_num_cells(5)
#> [1] 15360

# Get cell area in square meters
get_cell_area(10)
#> [1] 33201823

Todo's

Big inspiration from the h3o R package: [ ] make a5r work with the {sf} package for geometric operations. Mimick the h3_from_points et Co. [ ] define the A5 class as {vctrs}, to make it work seamlessly within a tidyverse workflow

License

Apache License 2.0

Acknowledgements

• A5 reference implementation by Felix Palmer
• A5 website
• A5 implementation in Rust
• Built with extendr
• Co-authored with Claude Code (Opus 4.5)