sampleRast: Sample random points from a raster with/out replacement

In enmSdmX: Species Distribution Modeling and Ecological Niche Modeling

Sample random points from a raster with/out replacement

Description

This function returns coordinates randomly located on a raster where cells can be sampled with replacement (if desired) and where the probability of selection is proportionate to the cell value, cell area, or the product of cell value times cell area.

Usage

sampleRast(x, n, adjArea = TRUE, replace = TRUE, prob = TRUE)

Arguments

x	SpatRaster object.
n	Positive integer. Number of points to draw.
adjArea	If TRUE (default) then adjust probabilities so sampling accounts for cell area.
replace	If TRUE (default) then sample with replacement.
prob	If TRUE (default) then sample cells with probabilities proportional to cell values. If adjArea is also TRUE then probabilities are drawn proportional to the product of cell area * the value of the cell.

Value

2-column matrix with longitude and latitude of random points.

See Also

spatSample

Examples

library(terra)
r <- rast()
nc <- ncell(r)
r[] <- 1:nc
rands1 <- sampleRast(r, 10000)
rands2 <- sampleRast(r, 10000, adjArea=FALSE)
rands3 <- sampleRast(r, 10000, prob=FALSE)
rands4 <- sampleRast(r, 10000, adjArea=FALSE, prob=FALSE)

oldPar <- par(mfrow=c(2, 2))

plot(r, main='adjArea = TRUE & prob = TRUE')
points(rands1, pch='.')
plot(r, main='adjArea = FALSE & prob = TRUE')
points(rands2, pch='.')
plot(r, main='adjArea = TRUE & prob = FALSE')
points(rands3, pch='.')
plot(r, main='adjArea = FALSE & prob = FALSE')
points(rands4, pch='.')

par(oldPar)

enmSdmX documentation built on April 3, 2025, 7:50 p.m.