Computes the AOO as the number of occupied grid cells multiplied by the cell area, following the IUCN Red List guidelines (reference scale: 2 x 2 km cells = 4 km^2 each) and the approach used by the ConR package. Points are snapped to a regular grid defined on a data-centred equal-area projection.
Arguments
- points
An
sfof POINT geometries (one species).- cell_km
Grid cell side length in kilometres (default
2).- n_rep
Integer; number of translated grids to test (default
100; the lattice is cheap, and more offsets bring the count closer to the true minimum). The minimum occupied-cell count over the replicates is returned.
Value
A list with area_km2, n_cells, cell_km,
cells (occupied cells as an sfc polygon set in WGS84) and
crs_laea.
Details
Because the occupied-cell count depends on where the grid is placed, this
function tests several translated grids and returns the smallest
count, as ConR does. The translations follow a deterministic, evenly spread
lattice, so the result is reproducible (no random seed needed). The returned
cells correspond to the grid placement that produced the reported
value.
Examples
f <- system.file("extdata", "example_occurrences.csv", package = "mappingAS")
occ <- read_occurrences(f)
sp1 <- occ[occ$species == occ$species[1], ]
calc_aoo(sp1)$area_km2
#> [1] 16