R/getBaiduMap.R

In daigazi/bamapr:

#' Get map from Baidu API
#'
#'
#' Take in coordiantes and return the location
#'
#'
#' @param location a vector a or matrix contains longtitude and latitude of the center of the map, or a character refers to the address
#' @param width width of the map
#' @param height height of the map
#' @param zoom map zoom, an integer from 3 (continent) to 21 (building), default value 10 (city)
#' @param scale multiplicative factor for the number of pixels returned. possible values are 2 or anything else.
#' @param color 'color' or 'bw', color or black-and-white
#' @param messaging logical. whether to print the download messages.
#' @return A ggmap object. a map image as a 2d-array of colors as hexadecimal strings representing pixel fill values.
#' @export
#' @importFrom png readPNG
#' @importFrom RgoogleMaps XY2LatLon
#' @importFrom ggmap ggmap
#' @examples
#'
#' \dontrun{
#' library(ggmap)
#' ## Beijing
#' p <- getBaiduMap(c(116.39565, 39.92999))
#' ggmap(p)
#'
#' p <- getBaiduMap('beijing') # the same
#' ggmap(p)
#'
#' ## black-and-white
#' p <- getBaiduMap(color='bw')
#' ggmap(p)
#'
#' ## do not print messages
#' p <- getBaiduMap(messaging = F)
#' }
getBaiduMap <- function(location, width = 400, height = 400, zoom = 10, 
    scale = 2, color = "color", messaging = TRUE) {
    ## location
    if (is.character(location) && length(location) == 1) {
        location_cor <- getCoordinate(location, formatted = T)
    } else if (length(location == 2)) {
        location_cor <- location
    } else {
        stop("Wrong address!")
    }
    lon <- location_cor[1]
    lat <- location_cor[2]
    
    ## set url
    url_head <- "http://api.map.baidu.com/staticimage?"
    url <- paste0(url_head, "width=", width, "&height=", height, "&center=", 
        lon, ",", lat, "&zoom=", zoom)
    if (scale == 2) 
        url <- paste0(url, "&scale=2")
    
    ## download image
    if (!"baiduMapFileDrawer" %in% list.dirs(full.names = F, recursive = F)) {
        dir.create("baiduMapFileDrawer")
    }
    destfile <- paste0(lon, ";", lat, ".png")
    download.file(url, destfile = paste0("baiduMapFileDrawer/", destfile), 
        quiet = !messaging, mode = "wb")
    if (messaging) 
        message(paste0("Map from URL : ", url))
    
    ## read image and transform to ggmap obejct
    map <- readPNG(paste0("baiduMapFileDrawer/", destfile))
    # format file
    if (color == "color") {
        map <- apply(map, 2, rgb)
    } else if (color == "bw") {
        mapd <- dim(map)
        map <- gray(0.3 * map[, , 1] + 0.59 * map[, , 2] + 0.11 * map[, 
            , 3])
        dim(map) <- mapd[1:2]
    }
    class(map) <- c("ggmap", "raster")
    
    # map spatial info
    ll <- XY2LatLon(list(lat = lat, lon = lon, zoom = zoom), -width/2 + 
        0.5, -height/2 - 0.5)
    ur <- XY2LatLon(list(lat = lat, lon = lon, zoom = zoom), width/2 + 
        0.5, height/2 - 0.5)
    
    # ll = as.numeric(rev(geoconv(rev(ll)))) ur =
    # as.numeric(rev(geoconv(rev(ur))))
    attr(map, "bb") <- data.frame(ll.lat = ll[1], ll.lon = ll[2], ur.lat = ur[1], 
        ur.lon = ur[2])
    
    # transpose
    out <- t(map)
    out
}