spatialEco (version 2.0-1)

background: Background sample

Description

Creates a point sample that can be used as a NULL for SDM's and other modeling approaches.

Usage

background(
  x,
  p = 1000,
  known = NULL,
  d = NULL,
  type = c("regular", "random", "hexagon", "nonaligned")
)

Value

A sf POINT feature class or data.frame with x,y coordinates

Arguments

x

A sf class polygon defining sample region

p

Size of sample

known

An sf POINT class of known locations with same CSR as x

d

Threshold distance for known proximity

type

Type of sample c("systematic", "random", "hexagon", "nonaligned")

Author

Jeffrey S. Evans <[e-mail]>

Examples

library(sf)

# define study area
sa <- suppressWarnings(st_cast(st_read(
        system.file("shape/nc.shp", 
        package="sf")), "POLYGON"))
  sa <- sa[10,]

# create "known" locations  
locs <- st_sample(sa, 50)
  st_crs(locs) <- st_crs(sa)

# systematic sample using extent polygon
e <- st_as_sf(st_as_sfc(st_bbox(sa)))
  st_crs(e) <- st_crs(sa)
s <- background(e, p=1000, known=locs, d=1000)
  plot(st_geometry(s), pch=20)
    plot(st_geometry(locs), pch=20, col="red", add=TRUE)

# systematic sample using irregular polygon
s <- background(sa, p=1000, known=locs, d=1000)
  plot(st_geometry(sa)) 
    plot(st_geometry(s), pch=20, add=TRUE)
      plot(st_geometry(locs), pch=20, col="red", add=TRUE)

# random sample using irregular polygon
s <- background(sa, p=500, known=locs, 
                d=1000, type="random")
  plot(st_geometry(sa)) 
    plot(st_geometry(s), pch=20, add=TRUE)
      plot(st_geometry(locs), pch=20, col="red", add=TRUE)