Convert cell coordinates to index string

Converts cell coordinates (face, i, j) to a hierarchical index string. The index type is selected from aperture when index_type = "auto".

Usage

hexify_cell_to_index(
  face,
  i,
  j,
  resolution,
  aperture = 3L,
  index_type = c("auto", "z3", "z7", "zorder")
)

Arguments

face

Face/quad numbers (0-19)

i

I coordinates

j

J coordinates

resolution

Resolution level

aperture

Aperture (3, 4, or 7)

index_type

Index encoding: "auto" (default), "z3", "z7", or "zorder"

Value

A character vector of index strings, one per cell. face, i and j are read in step and must be the same length.

Details

Default index types by aperture:

• Aperture 3: Z3 (optimized digit selection)

• Aperture 4: Z-order (Morton curve)

• Aperture 7: Z7 (one base-7 child digit per resolution)

A Z7 index has the form BBd1...dr, where BB is the two-digit base cell (00–11), r is the resolution, and every child digit is in 0–6. It is IGEO7's Z7 index, the string DGGRID writes for the same cell, and decoding and re-encoding a valid index returns the same string. BB is the pentagon the cell descends from, which need not be face. Under each pentagon one direction is missing: a string whose first nonzero digit is 2 (base cells 00–05) or 5 (06–11) names no cell.

See also

Other hierarchical index: hexify_compare_indices(), hexify_default_index_type(), hexify_get_children(), hexify_get_parent(), hexify_get_resolution(), hexify_index_to_cell(), hexify_index_to_lonlat(), hexify_is_valid_index_type(), hexify_lonlat_to_index(), hexify_z7_canonical()

Examples

idx <- hexify_cell_to_index(5, 10, 15, resolution = 3, aperture = 3)

# Aperture-7 indices contain a two-digit base cell and one digit per level
z7 <- hexify_cell_to_index(5, 1, 1, resolution = 2, aperture = 7)
nchar(z7) == 4L