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Cell size and counts by resolution

Source: R/info.R
a5_resolution_stats.Rd

Properties of the grid at a resolution, independent of any particular cell:

Usage

a5_cell_area(resolution, units = "m^2")

a5_cell_edge_length_avg(resolution, units = "m")

a5_get_num_cells(resolution)

a5_get_num_children(parent_resolution, child_resolution)

Arguments

resolution

Integer vector of resolutions (0–30). A scalar for a5_get_num_cells().

units

Character scalar giving the output unit: an area unit for a5_cell_area() (default "m^2"), a length unit for a5_cell_edge_length_avg() (default "m"). Any unit units::set_units() can convert to is accepted (e.g. "km^2", "ha", "km", "mi"). If NULL, a plain numeric vector in square metres or metres is returned.

parent_resolution, child_resolution

Integer scalars (0–30), with child_resolution at or finer than parent_resolution.

Value

  • a5_cell_area(), a5_cell_edge_length_avg(): a units::units vector the length of resolution, or numeric when units = NULL.

  • a5_get_num_cells(), a5_get_num_children(): a numeric scalar. Counts are doubles because they can exceed R's integer range.

Details

  • a5_cell_area(): the area of one cell. A5 is an equal-area grid, so every cell at a resolution has the same area.

  • a5_cell_edge_length_avg(): the average cell edge length. Individual edges vary from this by roughly +/-10%, depending on the cell's shape and position; use a5_cell_to_boundary() to measure a specific cell.

  • a5_get_num_cells(): the number of cells covering the globe.

  • a5_get_num_children(): the number of descendants each cell has at a finer resolution, as returned by a5_cell_to_children().

Use the first two to choose a resolution for a target cell size.

Examples

a5_cell_area(0:5)
#> Units: [m^2]
#> [1] 4.250547e+13 8.501094e+12 2.125273e+12 5.313184e+11 1.328296e+11
#> [6] 3.320740e+10
a5_cell_area(5, units = "km^2")
#> 33207.4 [km^2]
a5_cell_edge_length_avg(10, units = "km")
#> 4.675881 [km]

a5_get_num_cells(10)
#> [1] 15728640
a5_get_num_children(5, 8) # 4^3 = 64
#> [1] 64

# cells at a resolution times their area covers the globe
a5_get_num_cells(10) * a5_cell_area(10, units = "km^2")
#> 510065625 [km^2]