R/acorr_center.R

In AdamWilsonLab/rasterAutocorr: Quickly calculate spatial autocorrelation on 2D rasters.

#' Finds the center pixel to faciltate comparison of results from \code{acorr}.
#'
#'
#' @description Performs the following functions. 1) create an empty raster to hold the output, 2) fill the raster with NAs, 3) Set the center pixel equal to 1.
#' This faciliates using other functions in the \pkg{raster} package that calculate distance and direction to the closest non-NA pixel.  This is useful because the output of \code{\link{acorr}} returns the spatial autocorrelation for all directions simutaneously and thus needs to be linked to distance and direction to generate a correlogram.
#' @param x A raster* object
#' @return A raster object with all cells NA except the center pixel.
#' 



acorr_center=function(x){
  center = ceiling(dim(x)/2)
  # Create an empty raster to hold the output
  center2=x
  # Fill the raster with NAs
  values(center2)=NA
  # Replace the center pixel with a one  
  nre=ifelse(nrow(x)/2==round(nrow(x)/2),1,0)
  nce=ifelse(ncol(x)/2==round(ncol(x)/2),1,0)
  center2[center[1]+nre,center[2]+nce]=1
  return(center2)
}