R/strandkoder.R

In jonpeder/Insektlok: Obtain insect locality data from coordinates

#' strandkoder
#'
#' Returns Strand-codes from one, or a set of input coordinates (projection longlat, datum WGS84). The strand-codes are obtained by identifying the intesects beween the input coordinates and a polygon dataset of the Strand regions. This dataset was created by Endrestøl (2021), following the revision of the Strand-system by Økland (1981).
#' @param lon a numerical value, or vector of numerical values, that specifies the longitude(s) in the input coordinates
#' @param lat a numerical value, or vector of numerical values, that specifies the latitude(s) in the input coordinates
#' @return dataframe with Strand-codes
#' @examples example_output <- strandkoder(lat = c(69.57696, 70.44070, 62.259262), lon = c(24.840064, 23.186622, 12.734821))
#' @import sp
#' @import rgdal
#' @export

strandkoder <- function(lat, lon) {
  # Save longlat projection to variable
  ll_prj <- "+proj=longlat +datum=WGS84"
  # Import coordinates dataset
  lonlat <- data.frame(lon, lat)
  # Convert decimal-longlat to SpatialPoints class, with projection longlat datum wgs84
  pts <- SpatialPoints(lonlat, CRS(ll_prj))
  # Convert 'strand' spatial polygons dataframe to projection longlat and datum wgs84
  #strand.4.0 <- spTransform(strand, CRS(ll_prj))
  #kommuner <- spTransform(kommuner, CRS(ll_prj))
  # Identify municipalities intersecting with input coordinates
  strand_codes <- over(pts, strand)
  munic <- over(pts, kommuner)
  # get municipality names
  munic_names = NULL
  for (i in 1:length(lat)) {
    tmp = munic$navn[[i]][munic[[11]][[i]] == "nor"]
    if (is.null(tmp)) {tmp = NA}
    munic_names = c(munic_names, tmp)
  }
  # Return dataframe
  return(data.frame(strand = strand_codes[,2], municipality = munic_names, county = strand_codes[,4]))
}