Generate Background Sample Indices

Randomly selects valid (non-NODATA) cells from a reference grid for use as background points in MaxEnt modeling.

Usage

maxent_background_indices(grid, n = 10000L, seed = NULL)

Arguments

grid

External pointer to a GridFloat object used as a reference (e.g. an environmental layer). Only cells with valid data are eligible.

n

Integer: number of background points to sample (default 10000L).

seed

Integer or NULL: random seed for reproducibility. If NULL (default), no seed is set.

Value

A named list with:

rows

Integer vector of row indices (0-based).

cols

Integer vector of column indices (0-based).

indices

Integer vector of 0-based flat indices (row * ncols + col), suitable for maxent_featured_space.

Examples

# \donttest{
g <- maxent_grid_from_matrix(matrix(runif(100), 10, 10),
        -120, 35, 0.1, name = "env1")
bg <- maxent_background_indices(g, n = 50, seed = 42)
bg$indices  # 0-based flat indices for FeaturedSpace
#>  [1] 84 46 42 37 71 99 64 32  7 88 63 91 52 20  4 62 53 40 33 68 75 14 29 92 24
#> [26] 41 12 97 70 38 76 59 30 94 49 78 66 50 26 10 15  8 35  2  6 45 73 90 93 28
# }