#' R function for refined Nearest Neighbor analysis of point patterns (G function)
#'
#' The function allows to perform the refined Nearest Neighbor analysis of point patterns by plotting the cumulative Nearest Neighbour distance,
#' along with an acceptance interval (with significance level equal to 0.05;
#' sensu Baddeley et al., "Spatial Point Patterns. Methodology and Applications with R", CRC Press 2016, 208) based on B (set to 200 by default) realizations of a Complete Spatial Random process.
#' The function also allows to control for a first-order effect (i.e., influence of an underlaying numerical covariate) while performing the analysis.
#' The covariate must be of 'RasterLayer class'.\cr
#'
#' The function uses a randomized approach to build the mentioned acceptance interval whereby cumulative distributions of average NN distances of random points are computed across B iterations.
#' In each iteration, a set of random points (with sample size equal to the number of points of the input feature) is drawn.\cr
#'
#' Thanks are due to Dason Kurkiewicz for the help provided in writing the code to calculate the acceptance interval.
#'
#' @param feature: feature dataset (of point type).
#' @param studyplot: shapefile (of polygon type) representing the study area; if not provided, the study area is internally worked out as the convex hull enclosing the input feature dataset.
#' @param buffer: add a buffer to the studyplot (0 by default); the unit depends upon the units of the input data.
#' @param B: number of randomizations to be used (200 by default).
#' @param cov.var: numeric covariate (of RasterLayer class) (NULL by default).
#' @param order: integer indicating the kth nearest neighbour (1 by default).
#' @keywords refNNA
#' @export
#' @examples
#' data(springs)
#' refNNa(springs) #produces a plot representing the cumulative nearest neighbour distance distribution; a confidence envelope based on 1000 ranodmized simulations is also shown.
#'
#' data(Starbucks) #load the Startbucks datset
#' data(popdensity) #load the raster representing the numerical covariate
#' refNNa(Starbucks, cov.var=popdensity) #perform the analysis, controlling for the 1st order effect
#' @seealso \code{\link{NNa}}
#'
refNNa <- function (feature, studyplot=NULL, buffer=0, B=200, cov.var=NULL, order=1) {
#if there is no covariate data, workout the studyplot according to whether or not the studyplot is
#entered by the user; if it is not, the studyplot is the convex hull based on the points themselves;
#either way, the studyplot is eventually stored into the region object
if(is.null(cov.var)==TRUE){
if(is.null(studyplot)==TRUE){
ch <- rgeos::gConvexHull(feature)
region <- rgeos::gBuffer(ch, width=buffer)
} else {
region <- studyplot
}
#(if the covariate raster is provided; see above), then...
} else {
#tranform the cov.var from a RasterLayer to an object of class im, which is needed by spatstat
cov.var.im <- as.im(cov.var)
}
#for each point in the input feature dataset, calculate the distance to its nearest neighbor
dst <- spatstat::nndist(coordinates(feature), k=order)
#calculate the ECDF of the observed NN distances
dst.ecdf <- ecdf(dst)
#create a matrix to store the distance of each random point to its nearest neighbor;
#each column correspond to a random set of points
dist.rnd.mtrx <- matrix(nrow=length(feature), ncol=B)
#set the progress bar to be used later on within the loop
pb <- txtProgressBar(min = 0, max = B, style = 3)
#if there is no covariate data, draw random points within the study region
if(is.null(cov.var)==TRUE){
for (i in 1:B){
#draw a random sample of points within the study region
rnd <- sp::spsample(region, n=length(feature), type='random')
#calculate the NN distances of the random points and store them in the matrix (column-wise)
dist.rnd.mtrx[,i] <- spatstat::nndist(coordinates(rnd), k=order)
setTxtProgressBar(pb, i)
}
} else {
#if there is a covariate dataset
for (i in 1:B){
#draw random points via the spatstat's rpoint function,
#using the covariate dataset as spatial covariate
rnd <- spatstat::rpoint(n=length(feature), f=cov.var.im)
#calculate the NN distances of the random points and store them in the matrix (column-wise)
dist.rnd.mtrx[,i] <- spatstat::nndist(rnd, k=order)
setTxtProgressBar(pb, i)
}
}
# Make a list for the ecdfs
rnd.ecdfs <- list()
for(i in 1:ncol(dist.rnd.mtrx)){
rnd.ecdfs[[i]] <- ecdf(dist.rnd.mtrx[,i])
}
xlim = c(min(min(dist.rnd.mtrx), min(dst)), max(dst))
# We will evaluate the ecdfs on a grid of 1000 points between
# the x limits
xs <- seq(xlim[1], xlim[2], length.out = 1000)
# This actually gets those evaluations and puts them into a matrix
out <- lapply(seq_along(rnd.ecdfs), function(i){rnd.ecdfs[[i]](xs)})
tmp <- do.call(rbind, out)
# Get the .025 and .975 quantile for each column
# at this point each column is a fixed 'x' and the rows
# are the different ecdfs applied to that
lower <- apply(tmp, 2, quantile, probs = .025)
upper <- apply(tmp, 2, quantile, probs = .975)
#adjust the main plot title according to the presence of a covariate dataset
if(is.null(cov.var)==TRUE){
maintitle <- paste0("Refined Nearest Neighbor analysis (G function) \n(acceptance interval based on ", B, " randomized iterations)")
} else {
maintitle <- paste0("Refined Nearest Neighbor analysis (G function, controlling for the covariate effect) \n(acceptance interval based on ", B, " randomized iterations)")
}
# Plot the original data
# plot the ECDF of the first random dataset
plot(dst.ecdf,
verticals=TRUE,
do.points=FALSE,
col="white",
xlab="Nearest Neighbor distance (d)",
ylab="G (d)",
main=maintitle,
cex.main=0.90,
xlim= xlim)
# Add in the quantiles
polygon(c(xs,rev(xs)), c(upper, rev(lower)), col = "#DBDBDB88", border = NA)
plot(dst.ecdf,
verticals=TRUE,
do.points=FALSE,
add=TRUE)
}
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