BAS {spbal}

Balanced Acceptance Sampling (BAS).

Description

BAS draws spatially balanced samples from areal resources. To draw BAS samples, spbal requires a study region shapefile and the region’s bounding box. An initial sample size is also needed, which can be easily increased or decreased within spbal for master sampling applications

Usage

BAS(
  shapefile = NULL,
  n = 100,
  boundingbox = NULL,
  minRadius = NULL,
  panels = NULL,
  panel_overlap = NULL,
  stratum = NULL,
  seeds = NULL,
  verbose = FALSE
)

Arguments

shapefile

Shape file as a polygon (sp or sf) to select sites for.

n

Number of sites to select. If using stratification it is a named vector containing sample sizes of each group.

boundingbox

Bounding box around the study area. If a bounding box is not supplied then spbal will generate a bounding box for the shapefile.

minRadius

If specified, the minimum distance, in meters, allowed between sample points. This is applied to the $sample points. Points that meet the minRadius criteria are retuned in the minRadius output variable.

panels

A list of integers that define the size of each panel in a non-overlapping panels design. The length of the list determines the number of panels required. The sum of the integers in the panels parameter will determine the total number of samples selected, n. The default value for panels is NULL, this indicates that a non-overlapping panel design is not wanted.

panel_overlap

A list of integers that define the overlap into the previous panel. Is only used when the panels parameter is not NULL. The default value for panel_overlap is NULL. The length of panel_overlap must be equal to the length of panels. The first value is always forced to zero as the first panel never overlaps any region.

stratum

The name of a column in the data.frame attached to shapefile that defines the strata of interest.

seeds

A vector of 2 seeds, u1 and u2. If not specified, the default is NULL and will be defined randomly using function generateUVector.

verbose

Boolean if you want to see any output printed to screen. Helpful if taking a long time. Default is FALSE i.e. no informational messages are displayed.

Value

A list containing three variables, $sample containing locations in the BAS sample, in BAS order, $seeds, the u1 and u2 seeds used to generate the sample and $minRadius containing points from $sample that meet the minRadius criteria. If the minRadius parameter is NULL then the $minRadius returned will also be NULL.

The sample points are returned in the form of a simple feature collection of POINT objects. They have the following attributes:

• SiteID A unique identifier for every sample point. This encodes the BAS order.

• spbalSeqID A unique identifier for every sample point. This encodes the BAS sample order.

• geometry The XY co-ordinates of the sample point in the CRS of the original shapefile.

Author(s)

This function was first written by Paul van Dam-Bates for the package BASMasterSample and later simplified by Phil Davies.

Examples

# Equal probability BAS sample ----------------------------------------------

# Use the North Carolina shapefile supplied in the sf R package.
shp_file <- sf::st_read(system.file("shape/nc.shp", package="sf"))
shp_gates <- shp_file[shp_file$NAME == "Gates",]

# Vertically aligned master sample bounding box.
bb <- spbal::BoundingBox(shapefile = shp_gates)

set.seed(511)
n_samples <- 20
# Equal probability BAS sample.
result <- spbal::BAS(shapefile = shp_gates,
                     n = n_samples,
                     boundingbox = bb)
BAS20 <- result$sample
# display first three sample points.
BAS20[1:3,]

# Increase the BAS sample size ----------------------------------------------
n_samples <- 50
result2 <- spbal::BAS(shapefile = shp_gates,
                      n = n_samples,
                      boundingbox = bb,
                      seeds = result$seed)
BAS50 <- result2$sample
BAS50[1:3,]

# Check, first n_samples points in both samples must be the same.
all.equal(BAS20$geometry, BAS50$geometry[1:20])