R/get_map.R

In PawelMG/gis_server: Package facilitating the use of open map data

#####################################################################
# get_background function
#####################################################################

#' Locally storing and rendering OSM maps.
#'
#' The \code{get_background} function loads and plots pre-rendered map background. 
#'
#' @param map_data a path to the directory including maps.
#' @param xy a data frame of network graph's coordinates, with columns labelled 'Longitude' and 'Latitude'.
#' @param mapdb_name a character string with the name of the map database.
#' @param proj a string specifying the geographic projection of the network graph, e.g. "+init=epsg:4326".
#' @param init_proj a string specifying the geographic projection of the map database (by default "+init=epsg:4326").
#' @param options_list a set of mainly graphical parameters used by the rendering engine: 
#'        \describe{    
#'          \item{mscale}{specifies the scale of the map, e.g. 5000 stands for 1:5000 map,}
#'          \item{url}{an url to a map view on osm.org can be provided to define the bounding box if no coordinates are provided,}
#'          \item{wld}{this option specifies whether a so called world file should be printed; a world file explicitly specifies the
#'                     extent of a generated raster object; this option defaults to FALSE, as normally the coordinates are stored in the
#'                     map database,}
#'          \item{dpi}{a parameter specifying the optical resolution of the output map; default value is 200,}
#'          \item{paper}{an optional parameter specifying paper size of the output map, e.g 'a+4'; usually this option is not used,
#'                       as the map size is the product of scale, resolution and spatial extent,}
#'          \item{margin}{a parameter specifying the margin around the extent of the input object expressed as percent of the difference between xmax and xmin and ymax and ymin,}
#'          \item{size}{target map dimensions in mm (W x H, one 0 allowed),}
#'          \item{xmstyle}{mandatory argument, the full path to the xml style file for mapnik,}
#'          \item{output}{mandatory argument, specifies the name and most importantly the extension of the file;
#'                        default output format has been set to JPEG.}
#'          \item{tiles}{Write n x n tiles, then join using imagemagick montage command; this argument is used if the size of the map 
#'                       exceeds maximal mapnik output size; default value is FALSE; CAUTION: .pdf files can be output directly,
#'                       but are not valid for tiling, for a city the size of e.g. Szczecin (Poland) the highest available map scale
#'                       is ca. 1:7000.}
#'          \item{just_tiles}{Do not join tiles, instead write ozi/wld file for each; used only in conjunction with 'tiles',
#'                            defaults to FALSE.}
#'          \item{force_rend}{If there is no map fulfilling the desired criteria and the parameter is set to FALSE, there will be no attempt at
#'                            rendering. If the parameter is set as TRUE, a map with specified criteria will be rendered.}
#'        }    
#' 
#' @name get_background
#' @rdname gis_server-package
#' @export
#' @import RSQLite
#' @import DBI
#' @import sp
#' @import rgdal
#' @import rgeos
#' @import raster
#' @examples
#' ###########################################################
#'
#' # Loading the package
#' library(gisserver)
#'
#' # Generating artificial points
#'
#' Longitude <- runif(100, min =  20.9,  max = 21.05)
#' Latitude <- runif(100, min = 52.2, max = 52.25)
#' xy <- as.data.frame(cbind(Longitude, Latitude))
#'
#' # Setting the projection of the graph coordinates (proj) and the projection of the underlying map (init_proj)
#'
#' proj = "+init=epsg:4326" 
#' init_proj = "+init=epsg:4326" # default OSM coordinate reference system
#'
#' options_list  <- list(mscale = 29000,
#'                       url = NULL,
#'                       wld = FALSE,
#'                       dpi = 200,
#'                       paper = NULL,
#'                       margin = 0.01,
#'                       size = NULL,
#'                       xmstyle = "C:/GIS_data/osm_mapnik/gis.xml",
#'                       output  = "map.png",
#'                       tiles = FALSE,
#'                       just_tiles = FALSE,
#'						           force_rend = TRUE)
#' 
#' # Fetching the map background
#'
#' get_background(xy = xy,
#'               map_data = "extdata",
#'               mapdb_name = "MapID.db",
#'               proj = proj,
#'               init_proj = init_proj,
#'               options_list = options_list)
#' 
#' # Plotting the points on the background
#'
#' points(xy, col = 'red', lwd = 3)
#' 
#' ###########################################################

get_background <- function(xy, map_data = "extdata", mapdb_name = "MapID.db", proj, init_proj, options_list = NULL)
{
  
  # Specifying default rendering options
  
  def_options  <-  list(mscale = 50000,
                        url = NULL,
                        wld = FALSE,
                        dpi = 150,
                        paper = NULL,
                        margin = 0.05,
                        size = NULL,
                        xmstyle = "C:/GIS_data/osm_mapnik/gis.xml",
                        output  = "map.jpeg",
                        tiles = FALSE,
                        just_tiles = FALSE,
                        force_rend = FALSE)
  
  
  # Checking if specified options are correct
  if (!is.null(options_list)) {
    fitting_options <- which(names(options_list) %in% names(def_options))
    if (length(fitting_options) < length(options_list)) {
      warning('Unrecognised options were specified')
    }
    
    # Overwriting default options
    mo <- match(names(options_list[fitting_options]), names(def_options))
    def_options[mo] <- options_list[fitting_options]
    options_list <- def_options
  }
  
  # Coordinates of the network nodes are being transformed to the coordinate reference system of the map 
  # The bounding box (extent) is being constructed, and the database is queried for maps that encompass the graph
  
  sp::coordinates(xy) <- ~ Longitude + Latitude
  sp::proj4string(xy) <- sp::CRS(proj)
  xy <- sp::spTransform(xy, CRSobj = init_proj)
  ext_map <- raster::extent(xy)
  ext_map <- extent_margin(ext_map = ext_map,
                           margin = options_list$margin)
  
  
  db <- establish_con(map_data , mapdb_name)
  
  mapl <- check_map(db = db,
                    ext_map = ext_map,
                    options_list = options_list)
  
  if (!(length(mapl) > 1)){
    if(options_list$force_rend == TRUE){
      print("There is no map in the database covering the desired area or parameters. An attempt will be made to render the map.")  
      
      render_map(options_list = options_list,
                 map_data = map_data,
                 ext_map = ext_map,
                 db = db)
      
      mapl <- save_map(options_list = options_list,
                       init_proj = init_proj,
                       ext_map = ext_map,
                       map_data = map_data,
                       db = db)
      
      dbDisconnect(db)
      
      load_map(mapl = mapl,
               map_data = map_data,
               ext_map = ext_map)				 
    }
    if(options_list$force_rend == FALSE){
      print("There is no map in the database satisfying the criteria")
      dbDisconnect(db)
    }
  }
  
  if ((length(mapl) > 1)){
    load_map(mapl = mapl,
             map_data = map_data,
             ext_map = ext_map)	    
  }
}