R/read.hdr.r

In freysimon/ZAMGR: Collection of functions for reading and writing ZAMG raster products

#' Read an HDR file
#' @description Read an HDR file which is the header part of a BIL raster file
#' @author Simon Frey
#' @export
#' @import stringr
#' @return a data.frame containing the arguments of the hdr file
#' @param file character string. Filename of the file to be read.
#' @param add.nblocks logical. Should the agrument nblocks be added to the output? See details.
#' @param bandorder character string or NULL. If NULL no changes in the parameter layout are made, else the string of bandorder is used in the hdr file for the parameter layout.
#' @param noValue numerical or NULL. Sets the noValue argument in the hdr file.
#' @details If add.nblocks is TRUE (the default) then the argument \code{nblocks} is added to the output list (if it does nikt already exist).
#'     If so, the value from the argument \code{nbands} is copied to \code{nblocks} and \code{nbands} is set to 1. This is because of handling
#'     in Delft-FEWS. See the wiki of Delft-FEWS: (https://publicwiki.deltares.nl/display/FEWSDOC/BIL+BIP+BSQ+Parser).
#'

read.hdr <- function(file, add.nblocks = TRUE, bandorder = NULL, noValue = NULL){

  hdr <- scan(file = file, what = "character", blank.lines.skip = F)

  # Determine the arguments section of the file
  end.of.args <- which(hdr == "")[1]
  if(!is.na(end.of.args)){ # will be NA if no blank line is present in the file
    nlines <- floor(end.of.args/2)
  } else {
    nlines <- floor(length(hdr))
  }

  hdr <- read.table(file, header=F, nrows = nlines, colClasses = "character", stringsAsFactors = FALSE)

  if(add.nblocks){
    # check if nblocks already exists
    nblocks.exists <- any(stringr::str_detect(hdr[,1],"(?i)nblocks"))# ?i makes the regex case insensitive
    if(!nblocks.exists){
      nbands <- which(stringr::str_detect(hdr[,1],"(?i)nbands"))# ?i makes the regex case insensitive
      hdr <- rbind(hdr, c(ifelse(toupper(hdr[1,1]) == hdr[1,1],"NBLOCKS","nblocks"), hdr[nbands,2]))
      hdr[nbands,2] <- 1
    }
  }
  if(!is.null(bandorder)){
      bo <- which(stringr::str_detect(hdr[,1],"(?i)layout"))# ?i makes the regex case insensitive
      hdr[bo,2] <- toupper(bandorder)
  }

  if(!is.null(noValue)){
    nv <- which(stringr::str_detect(hdr[,1],"(?i)nodata"))# ?i makes the regex case insensitive
    hdr[nv,2] <- noValue
  }


  return(hdr)
}