sample_systematic: Systematic sampling

In tgoodbody/sgsR: Structurally Guided Sampling

Systematic sampling

Description

Systematic sampling with random start point and translation within a square or hexagonal tessellation.

Usage

sample_systematic(
  raster,
  cellsize,
  square = TRUE,
  location = "centers",
  force = FALSE,
  access = NULL,
  buff_inner = NULL,
  buff_outer = NULL,
  plot = FALSE,
  filename = NULL,
  overwrite = FALSE,
  details = FALSE,
  ...
)

Arguments

raster	spatRaster. Raster used to define extent of fishnet grid.
cellsize	Numeric. Desired cellsize for tessellation.
square	Logical. Tessellation shape. Default is regular square grid, if FALSE hexagons are used.
location	Character. Sample location within tessellation. Default = "centers") returns samples at tessellation centers, "corners" - corners of tessellation are returned, "random" - samples are randomly located within tessellations.
force	Logical. Only applies when location = "random". If TRUE, random samples are forced to fall in areas where raster does not have NA values. This will considerably slow processing.
access	sf. Road access network - must be lines.
buff_inner	Numeric. Inner buffer boundary specifying distance from access where plots cannot be sampled.
buff_outer	Numeric. Outer buffer boundary specifying distance from access where plots can be sampled.
plot	Logical. Plots output strata raster with samples.
filename	Character. Path to write output samples.
overwrite	Logical. Choice to overwrite existing filename if it exists.
details	Logical. If FALSE (default) output is sf object of systematic samples. If TRUE returns a list of sf objects where tessellation is the tessellation grid for sampling, and samples are the systematic samples.
...	Additional arguments for st_make_grid. Options include offset to offset grid by providing lower left coordinates.

Value

An sf object with sampled points over a tessellation.

Note

Specifying location = "random" can result in tessellations with no samples. This results from raster have NA values at the random location chosen. Using force = TRUE removes areas of NA from sampling entirely, but considerably slows processing speeds. Thanks to R. Hijmans for help in debugging and providing suggestions for this script.

Author(s)

Tristan R.H. Goodbody, Lukas Winiwarter

See Also

Other sample functions: sample_ahels(), sample_balanced(), sample_clhs(), sample_existing(), sample_nc(), sample_srs(), sample_strat(), sample_sys_strat()

Examples

#--- Load raster and access files ---#
r <- system.file("extdata", "mraster.tif", package = "sgsR")
mr <- terra::rast(r)
#--- perform grid sampling ---#
sample_systematic(
  raster = mr,
  cellsize = 1000
)

sample_systematic(
  raster = mr,
  cellsize = 1000,
  location = "corners",
  plot = TRUE
)

sample_systematic(
  raster = mr,
  cellsize = 1000,
  square = FALSE,
  location = "random",
  plot = TRUE
)

tgoodbody/sgsR documentation built on March 7, 2024, 2:20 a.m.