R/state_plane.R

In USAboundaries: Historical and Contemporary Boundaries of the United States of America

#' Projections from the State Plane Coordinate System
#'
#' Get EPSG codes or PROJ.4 codes for projections from the
#' \href{https://en.wikipedia.org/wiki/State_Plane_Coordinate_System}{State
#' Plane Coordinate System}.
#'
#' @param state The postal code for the state.
#' @param plane_id The state plane geographic zone identifier. A \code{NULL}
#'   value will return a projection for the entire state.
#' @param type The type of output to return: either an EPSG code or PROJ4
#'   string.
#'
#' @return Either a PROJ4 string as a character vector or an EPSG code as an
#'   integer.
#'
#' @seealso For documentation of the underlying State Plane Coordinate System
#'   projection data frame, see \code{\link{state_proj}}.
#'
#' @examples
#' if (require(USAboundariesData)) {
#'   state_plane(state = "MA", type = "epsg")
#'   state_plane(state = "MA", type = "proj4")
#'   state_plane(state = "MA", plane_id = "island", type = "epsg")
#'   state_plane(state = "MA", plane_id = "island", type = "proj4")
#'
#'   # Show the difference made by a state plane projection
#'   if (require(sf)) {
#'     va <- us_states(states = "VA", resolution = "high")
#'     plot(st_geometry(va), graticule = TRUE)
#'     va <- st_transform(va, state_plane("VA"))
#'     plot(st_geometry(va), graticule = TRUE)
#'   }
#' }
#'
#' @export
state_plane <- function(state, plane_id = NULL, type = c("epsg", "proj4")) {
  type <- match.arg(type)
  stopifnot(state %in% unique(state_proj$state))
  state_regions <- state_proj[state_proj$state == state, ]
  if (!is.null(plane_id)) {
    plane_id <- tolower(plane_id)
  }
  stopifnot(is.null(plane_id) || plane_id %in% unique(state_regions$zone))
  if (is.null(plane_id) && type == "epsg") {
    item <- state_proj[["epsg"]][state_proj$state == state & state_proj$statewide_proj == TRUE]
    item <- as.integer(item)
  } else if (is.null(plane_id) && type == "proj4") {
    item <- state_proj[["proj4_string"]][state_proj$state == state & state_proj$statewide_proj == TRUE]
  } else if (type == "epsg") {
    item <- state_proj[["epsg"]][state_proj$state == state & state_proj$zone == plane_id]
    item <- as.integer(item)
  } else if (type == "proj4") {
    item <- state_proj[["proj4_string"]][state_proj$state == state & state_proj$zone == plane_id]
  }
  item
}