Download Hex9's Warp Field

Hex9's own projection (hex_grid(aperture = 9, projection = "akw")) is Kaseorg's octahedral projection with an area-correcting warp that Griffin trained by optimal transport and publishes with 'libhex9', his reference implementation (Griffin 2026, Sec. 11b). The field is 19 MB of stored displacements and gradients, which hexify reads but does not ship; this function downloads it once from the 'libhex9' repository, checks it, and saves it where hexify looks for it.

Usage

hex9_warp_download(path = hex9_warp_path(), quiet = FALSE)

Arguments

path

Where to save the field. The default is hexify's user data directory (tools::R_user_dir("hexify", "data")), or the option hexify.hex9_warp when set; hexify reads it from the same place.

quiet

Passed to utils::download.file().

Value

The path of the saved file, invisibly.

Details

The file is 'libhex9”s core/Sphere_l6_fund.f64g.h9warp at the commit of version 2.3.1, which the Hex9 agreement checks in hexify were run against. 'libhex9' is Apache-2.0 licensed. Its field is defined on the unit sphere: 'libhex9”s WGS84 functions first turn geodetic latitude into authalic latitude, while hexify reads latitude as spherical latitude, as 'libhex9”s _sphere functions do.

References

Griffin, B. (2026). Hex9: A Quasi-Authalic, Quasi-Continuous Hexagonal DGGS on the Reference Ellipsoid. arXiv:2608.00022.

Examples

if (interactive()) {
  hex9_warp_download()
  g <- hex_grid(resolution = 5, aperture = 9, projection = "akw")
  lonlat_to_cell(16.37, 48.21, g)
}