R/wpGetBlocksNeed.R

In worldpopglobal/wpUtilities: Data Analysis and Modeling Package from WorldPop

# Authors: Maksym Bondarenko mb4@soton.ac.uk
# Date :  October 2017
# Version 0.1
#
#' wpGetBlocksNeed function will return a number of blocks
#' sugesting for processing raster file. It will take into consideration
#' number of layers, cells, cores and avalible memory on computer
#' (not maximum memory but avalible)
#' @param x raster
#' @param cores number of cores
#' @param n parameter to increase requrement of the raster
#' @param number_type Will be used to estimate requred memory
#' @rdname wpGetBlocksNeed
#' @return integer
#' @export
#' @examples
#' wpGetBlocksNeed( x, cores=2, n=1 )
#'
wpGetBlocksNeed <- function(x, cores, n=1, number_type = "numeric"){

  #stopifnot(hasValues(x))

  n <- n + nlayers(x) - 1
  cells <- round( 1.1 * ncell(x) ) * n
  #memneed <- cells * 8 * n / (1024 * 1024)

  if(number_type == "integer") {

      byte_per_number = 4

  } else if(number_type == "numeric") {

      byte_per_number = 8

  } else {

    #byte_per_number = .Machine$sizeof.pointer
    stop(sprintf("Unknown number_type: %s", number_type))
  }

  blocks <- 1

  memneed <- (cells * byte_per_number * n / (1024 * 1024 * 1024))/blocks

  memavail <- wpGetAvalMem()/cores

  while ((memneed > memavail)) {

    memneed <- (cells * byte_per_number * n / (1024 * 1024 * 1024))/blocks
    blocks <- blocks + 1
  }

  if ( blocks < cores) blocks <- cores

  return(blocks)

}