get_nearest_point: Function to select nearest community to a given sampling...

In validmeasures/spatialsampler: An Implementation of the Centric Systematic Area Sampling (CSAS) and Simple Spatial Sampling Method (S3M) sampling approaches in R

Description

Function to select nearest community to a given sampling point (usually the centroid of a square grid for CSAS or of a hexagonal grid for S3M) using geodesic calculations based on a specified reference ellipsoid

Usage

get_nearest_point(
  data,
  data.x,
  data.y,
  query,
  n = 1,
  ellipsoid = c("AA", "AN", "??", "BR", "BN", "CC", "CD", "EB", "EA", "EC", "EF", "EE",
    "ED", "RF", "HE", "HO", "ID", "IN", "KA", "AM", "FA", "SA", "WD", "WE"),
  duplicate = FALSE
)

Arguments

data	An input data frame or matrix containing longitude and latitude coordinates of village locations from which to find nearest neighbour
data.x	A character value specifying the variable name in data containing the longitude coordinates
data.y	A character value specifying the variable name in data containing the latitude coordinates
query	an object of class 'SpatialPoints' containing sampling point locations. This is usually the output from applying 'spsample()' function from package 'gstat' to create an even spatial sample across the entire sampling area
n	Number of nearest villages to select
ellipsoid	Two letter character value specifying the reference ellipsoid to use for distance calculations
duplicate	Logical. Specify if duplicate selected villages are to be kept or discarded. Default is FALSE (discard).

Value

A subset data frame of data of selected villages/communities nearest to the sampling points with a new variable d indicating the distance of the village/community to the sampling point (in kms). If duplicate is TRUE, the result has number of rows equal to nrow(query)

Author(s)

Ernest Guevarra <[e-mail]>

Examples

# Use get_nearest_point() with test sampling points in Sennar to find 3 nearest
#communities from the sampling points
sennar <- subset(sudan01, STATE == "Sennar")
samp.points <- sp::spsample(sennar, type = "hexagonal", n = 10)
get_nearest_point(data = sennar_villages, data.x = "x", data.y = "y",
                  query = samp.points, n = 3)

validmeasures/spatialsampler documentation built on Oct. 16, 2021, 3:15 a.m.