Sample annulus

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

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

Arguments

x	sp SpatialPoints or SpatialPointsDataFrame class object
r1	Numeric value defining inner radius of annulus (in projection units)
r2	Numeric value defining outer radius of annulus (in projection units)
n	Number of samples
...	Additional arguments passed to spsample

Value

sp SpatialPointsataFrame OBJECT

Note

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

Author

Jeffrey S. Evans <jeffrey_evans@tnc.org>

Examples

library(sp)
library(rgeos)
data(meuse)
coordinates(meuse) <- ~x+y
proj4string(meuse) <- CRS("+init=epsg:28992")
#> Warning: Discarded datum Amersfoort in Proj4 definition
xy <- meuse[2,]

rs100 <- sample.annulus(xy, r1=50, r2=100, n = 50, type = "random")
#> Warning: CRS object has comment, which is lost in output
rs200 <- sample.annulus(xy, r1=100, r2=200, n = 50, type = "random")
#> Warning: CRS object has comment, which is lost in output

plot(rs200, pch=20, col="red")
  points(rs100, pch=20, col="blue")
  points(xy, pch=20, cex=2, col="black")
  box()
  legend("topright", legend=c("50-100m", "100-200m", "source"), 
         pch=c(20,20,20), col=c("blue","red","black"))