R/wkt.R

In SymbolixAU/googlePolylines: Encoding Coordinates into 'Google' Polylines

#' Polyline WKT
#' 
#' Converts encoded polylines into well-known text. 
#' 
#' @param obj \code{sfencoded} object or \code{encoded_column} of encoded polylines
#' 
#' @return well-known text representation of the encoded polylines
#' 
#' @examples 
#' \dontrun{
#' 
#' library(sf)
#' nc <- sf::st_read(system.file("shape/nc.shp", package="sf"))
#' 
#' ## encode to polylines
#' enc <- encode(nc)
#' 
#' ## convert encoded lines to well-known text
#' wkt <- polyline_wkt(enc)
#' 
#' }
#' 
#' @note This will not work if you have specified \code{strip = TRUE} for \code{encode()}
#' 
#' @details
#' 'Polylines' refers to lat/lon coordinates encoded into strings using Google's 
#' polyline encoding algorithm.
#' 
#' The function assumes Google Web Mercator projection (WSG 84 / EPSG:3857 / EPSG:900913)
#' for inputs and outputs.
#' 
#' @export
polyline_wkt <- function(obj) UseMethod("polyline_wkt")

#' @export
polyline_wkt.sfencoded <- function(obj) {
  
  if(is.null(attr(obj, "encoded_column"))) stop("Can not find the encoded_column")
 
  geomCol <- attr(obj, "encoded_column")

  obj[[geomCol]] <- polyline_wkt(obj[[geomCol]])

  attr(obj[[geomCol]], "class") <- c("wkt_column", class(obj[[geomCol]] ) )
  
  attr(obj, "encoded_column") <- NULL
  attr(obj, "wkt_column") <- geomCol
  return(obj)
}

#' @export
polyline_wkt.sfencodedLite <- polyline_wkt.sfencoded

#' @export
polyline_wkt.encoded_column <- function(obj) rcpp_polyline_to_wkt(obj)


#' @export
polyline_wkt.default <- function(obj) stop(paste0("I was expecting an sfencoded object or an encoded_column"))


#' WKT Polyline
#' 
#' Converts well-known text into encoded polylines.
#' 
#' @param obj \code{sfencoded} object or \code{wkt_column} of well-known text
#' 
#' @return encoded polyline representation of geometries
#' 
#' @examples 
#' \dontrun{
#' 
#' library(sf)
#' nc <- sf::st_read(system.file("shape/nc.shp", package="sf"))
#' 
#' ## encode to polylines
#' enc <- encode(nc)
#' 
#' ## convert encoded lines to well-known text
#' wkt <- polyline_wkt(enc)
#' 
#' ## convert well-known text back to polylines
#' enc2 <- wkt_polyline(wkt)
#' 
#' }
#' 
#' @details
#' 'Polylines' refers to lat/lon coordinates encoded into strings using Google's 
#' polyline encoding algorithm.
#' 
#' @export
wkt_polyline <- function(obj) UseMethod("wkt_polyline")

#' @export
wkt_polyline.sfencoded <- function(obj) {
  
  if(is.null(attr(obj, "wkt_column"))) stop("Can not find the wkt_column")
  
  geomCol <- attr(obj, "wkt_column")
  
  obj[[geomCol]] <- wkt_polyline(obj[[geomCol]])
  
  attr(obj[[geomCol]], "class") <- c("encoded_column", class(obj[[geomCol]]))
  
  attr(obj, "wkt_column") <- NULL
  
  attr(obj, "encoded_column") <- geomCol
  return(obj)
}

#' @export
wkt_polyline.wkt_column <- function(obj) rcpp_wkt_to_polyline(obj)

#' @export
wkt_polyline.default <- function(obj) stop(paste0("I was expecting an sfencoded object with a wkt_column"))