spatialEco (version 2.0-2)

sample.annulus: Sample annulus

Description

Creates sample points based on annulus with defined inner and outer radius

Usage

sample.annulus(x, r1, r2, size = 10, ...)

Value

sf POINTS object

Arguments

x

An sf POINT class object

r1

Numeric value defining inner radius of annulus (in projection units)

r2

Numeric value defining outer radius of annulus (in projection units)

size

Number of samples

...

Additional arguments passed to sf::st_sample

Author

Jeffrey S. Evans <[e-mail]>

Details

Function can be used for distance based sampling which is a sampling method that can be used to capture spatially lagged variation.

Examples

 library(sf)
 if(require(sp, quietly = TRUE)) {
   data(meuse, package = "sp")
   meuse <- st_as_sf(meuse, coords = c("x", "y"), crs = 28992, 
                     agr = "constant")

 xy <- meuse[2,]
 rs100 <- sample.annulus(xy, r1=50, r2=100, size = 50)
 rs200 <- sample.annulus(xy, r1=100, r2=200, size = 50)
 
 plot(st_geometry(rs200), pch=20, col="red")
   plot(st_geometry(rs100), pch=20, col="blue", add=TRUE)
   plot(st_geometry(xy), pch=20, cex=2, col="black", add=TRUE)
 legend("topright", legend=c("50-100m", "100-200m", "source"), 
        pch=c(20,20,20), col=c("blue","red","black"))

# \donttest{
# Run on multiple points
rs100 <- sample.annulus(meuse[1:3,], r1=50, r2=100, 
                        size = 50)
rs200 <- sample.annulus(meuse[1:3,], r1=50, r2=200, 
                        size = 50)
plot(st_geometry(rs200), pch=20, col="red")
  plot(st_geometry(rs100), pch=20, col="blue", add=TRUE)
    plot(st_geometry(meuse[1:3,]), pch=20, cex=2, col="black", add=TRUE)
 legend("topright", legend=c("50-100m", "100-200m", "source"), 
        pch=c(20,20,20), col=c("blue","red","black"))
# }
} else { 
  cat("Please install sp package to run example", "\n")
}