R/shp_to_geojson.R

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#' Create GeoJSON from Shapefile
#'
#' Create GeoJSON file needed for interactive map in Shiny app
#'
#' @param shp path to shapefile with .shp extension, needs rgn_id and rgn_name fields
#' @param js path to output javascript file with variable 'regions' of geojson content
#' @param geojson path to output GeoJSON file. defaults to *.geojson of *.js file.
#'
#' @details Uses rgdal to write GeoJSON.
#'
#' @keywords geojson shapefile
#' @export
shp_to_geojson = function(shp, js, geojson=sprintf('%s.geojson', tools::file_path_sans_ext(js))){

  # # debug
  # shp      = '/Volumes/data_edit/git-annex/clip-n-ship/data/Albania/rgn_offshore_gcs.shp'
  # js      = '/Volumes/data_edit/git-annex/clip-n-ship/data/Albania/regions_gcs.js'
  # geojson = sprintf('%s.geojson', tools::file_path_sans_ext(js))

  # vars
  flds = c('rgn_id'='rgn_id', 'rgn_name'='rgn_nam') #flds = c('rgn_id'='region_id', 'rgn_nam'='region_nam') # too long for shapefile columns

  # check shp exists
  stopifnot(file.exists(shp))

  # read shp
  lyr = tools::file_path_sans_ext(basename(f_shp))
  x = st_read(dsn=shp, layer=lyr) #  proj4string=sp::CRS('+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs')

  # check fields present
  stopifnot(names(flds) %in% names(x))

  # drop other fields
  x@data = plyr::rename(x@data[,names(flds)], flds)

  # write geojson
  if (file.exists(geojson)) unlink(geojson)
  output_filename <- paste0(file_path_sans_ext(geojson), ".geojson")

  # Write the GeoJSON file
  st_write(obj = x, dsn = output_filename, driver = "GeoJSON")
  file.rename(tools::file_path_sans_ext(geojson), geojson)

  # write javascript
  fw = file(js, 'wb')
  cat('var regions = ', file=fw)
  cat(readLines(geojson, n = -1), file=fw)
  close(fw)
}