randomPoints
From dismo v1.14
by Robert Hijmans
Random points
Generate random points that can be used to extract background values ("randomabsence"). 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.
 Keywords
 spatial
Usage
randomPoints(mask, n, p, ext=NULL, extf=1.1, excludep=TRUE, prob=FALSE, cellnumbers=FALSE, tryf=3, warn=2, lonlatCorrection=TRUE)
Arguments
 mask
 Raster* object. 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
 Extent object. 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  prob
 logical. If
TRUE
the values inmask
are interpreted as probability weights (and the values should be positive numbers (or NA)). NOTE: this currently only works for rasters of a relatively modest size (that can be loaded into RAM)  cellnumbers
 logical. If
TRUE
, cell numbers for ]codemask 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  lonlatCorrection
 logical. If
TRUE
then correct for the fact that longitude/latitude is not a planar coordinate system
Value

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