backgroundSample {predicts}

Random points

Description

Generate random points that can be used to extract background values ("random-absence"). The points are sampled (without replacement) from the cells that are not 'NA' in raster 'mask'.

If the coordinate reference system (of mask) is longitude/latitude, sampling is weighted by the size of the cells. That is, because cells close to the equator are larger than cells closer to the poles, equatorial cells have a higher probability of being selected.

Usage

backgroundSample(mask, n, p, ext=NULL, extf=1.1, excludep=TRUE, 
             cellnumbers=FALSE, tryf=3, warn=2)

Arguments

mask

SpatRaster. If the object has cell values, cells with NA are excluded (of the first layer of the object if there are multiple layers)

n

integer. Number of points

p

Presence points (if provided, random points won't be in the same cells (as defined by mask)

ext

SpatExtent. Can be used to restrict sampling to a spatial extent

extf

numeric. Multiplyer to adjust the size of extent 'ext'. The default increases of 1.1 increases the extent a little (5% at each side of the extent)

excludep

logical. If TRUE, presence points are exluded from background

cellnumbers

logical. If TRUE, cell numbers for mask are returned rather than coordinates

tryf

numeric > 1. Multiplyer used for initial sample size from which the requested sample size is extracted after removing NA points (outside of mask)

warn

integer. 2 or higher gives most warnings. 0 or lower gives no warnings if sample size n is not reached

Value

matrix with coordinates, or, if cellnumbers=TRUE, a vector with cell numbers.