a5_cell_children_range: Range of descendant cell ids

In a5R: 'A5' Discrete Global Grid System

Range of descendant cell ids

Description

Returns the smallest and largest descendant of each cell at a finer resolution, without enumerating the descendants. Because the A5 index encodes position along a space-filling curve with a cell's descendants sharing its leading bits, the descendants of a cell at any resolution up to 29 occupy a contiguous range of ids among all cells at that resolution: every cell at child_resolution whose id lies between lo and hi inclusive is a descendant, and no descendant lies outside. This makes ⁠BETWEEN lo AND hi⁠ an exact filter on a store of child_resolution cells sorted by id. Not every integer in the range is a valid cell, and cells of other resolutions may fall inside it.

Usage

a5_cell_children_range(cell, child_resolution)

Arguments

cell	An a5_cell vector.
child_resolution	Integer scalar target resolution from 0 to 29, at or finer than every cell's own resolution.

Details

Resolution 30 is refused because the guarantee does not hold there. The index has no room for the usual face bits at that resolution, so faces use three different bit layouts whose id ranges overlap numerically, and a range can contain valid resolution-30 cells from another face. Eighteen of the sixty faces cannot be encoded at resolution 30 at all; the upstream library falls back to resolution 29 for them. Use a5_cell_to_children() if you need resolution-30 descendants.

Value

A data frame with a5_cell columns lo and hi, one row per input cell. NA where cell is NA.

See Also

a5_cell_to_children(), a5_cell_to_arrow() for exact 64-bit ids to pass to SQL.

Examples

cell <- a5_lonlat_to_cell(-3.19, 55.95, resolution = 5)
rng <- a5_cell_children_range(cell, child_resolution = 8)
children <- vctrs::vec_sort(a5_cell_to_children(cell, child_resolution = 8))
identical(rng$lo, children[1])
identical(rng$hi, children[length(children)])

a5R documentation built on Oct. 19, 2026, 5:08 p.m.