get_utm_crs

# funzioni necessarie

find_UTM_zone <- function(longitude, latitude) {

  # Special zones for Svalbard and Norway
  if (latitude >= 72.0 && latitude < 84.0 )
    if (longitude >= 0.0  && longitude <  9.0)
      return(31);
  if (longitude >= 9.0  && longitude < 21.0)
    return(33)
  if (longitude >= 21.0 && longitude < 33.0)
    return(35)
  if (longitude >= 33.0 && longitude < 42.0)
    return(37)

  (floor((longitude + 180) / 6) %% 60) + 1
}


find_UTM_hemisphere <- function(latitude) {
 ifelse(latitude > 0, "north", "south")
}

# Dato un poligono, tova il centroide in latlon

poly_centr <- poly %>%
      sf::st_bbox() %>%
      sf::st_as_sfc() %>%
      sf::st_centroid() %>%
      sf::st_transform(4326)

# Determina UTM zone e crea EPSG corrispondente (crs_utm)
      
    utm_zone <- find_UTM_zone(sf::st_coordinates(poly_centr)[1],
                              sf::st_coordinates(poly_centr)[2])
    utm_hem <- find_UTM_hemisphere(sf::st_coordinates(poly_centr)[2])
    if (utm_hem == "north") {
      crs_utm <- st_crs(as.numeric(paste0("326", utm_zone)))
    } else {
      crs_utm <- st_crs(as.numeric(paste0("327", utm_zone)))
    }