R/get_map_data.R

In nmcdev/nmcMetIO: Meteorological Data IO in NMC.

#' Define image size variables from the given bounding box coordinates.
#'
#' @param bbox bounding box coordinates (list of 2 points with long/lat values)
#' @param major_dim major image dimension, in pixels. 
#'                  Default is 400 (meaning larger dimension will be 400 pixels)
#'
#' @return list with items "width", "height", and "size" (string of format "width,height")
#' @export
#'
#' @examples
#' bbox <- list(
#'   p1 = list(long = -122.522, lat = 37.707),
#'   p2 = list(long = -122.354, lat = 37.84)
#' )
#' image_size <- define_image_size(bbox, 600)
#' 
define_image_size <- function(bbox, major_dim = 400) {
  require(magrittr)
  # calculate aspect ration (width/height) from lat/long bounding box
  aspect_ratio <- abs((bbox$p1$long - bbox$p2$long) / (bbox$p1$lat - bbox$p2$lat))
  # define dimensions
  img_width <- ifelse(aspect_ratio > 1, major_dim, major_dim*aspect_ratio) %>% round()
  img_height <- ifelse(aspect_ratio < 1, major_dim, major_dim/aspect_ratio) %>% round()
  size_str <- paste(img_width, img_height, sep = ",")
  list(height = img_height, width = img_width, size = size_str)
}


#' Translate the given long/lat coordinates into an image position (x, y).
#'
#' @param long longitude value
#' @param lat latitude value
#' @param bbox bounding box coordinates (list of 2 points with long/lat values)
#' @param image_width image width, in pixels
#' @param image_height image height, in pixels
#'
#' @return named list with elements "x" and "y" defining an image position
#' @export
#'
find_image_coordinates <- function(long, lat, bbox, image_width, image_height) {
  x_img <- round(image_width * (long - min(bbox$p1$long, bbox$p2$long)) / abs(bbox$p1$long - bbox$p2$long))
  y_img <- round(image_height * (max(bbox$p1$lat, bbox$p2$lat)-lat) / abs(bbox$p1$lat - bbox$p2$lat))
  list(x = x_img, y = y_img)
}


#' Download a map image from the ArcGIS REST API
#'
#' @param bbox bounding box coordinates (list of 2 points with long/lat values)
#' @param map_type map type to download - options are World_Street_Map, World_Imagery, World_Topo_Map
#' @param file file path to save to. Default is NULL, which will create a temp file.
#' @param width image width (pixels)
#' @param height image height (pixels)
#' @param sr_bbox Spatial Reference code for bounding box
#' 
#' @details This function uses the ArcGIS REST API, specifically the 
#' "Execute Web Map Task" task. You can find links below to a web UI for this
#' rest endpoint and API documentation.
#' 
#' Web UI: https://utility.arcgisonline.com/arcgis/rest/services/Utilities/PrintingTools/GPServer/Export%20Web%20Map%20Task/execute
#' API docs: https://developers.arcgis.com/rest/services-reference/export-web-map-task.htm
#'
#' @return file path for the downloaded .png map image
#' @export
#'
#' @examples
#' bbox <- list(
#'   p1 = list(long = -122.522, lat = 37.707),
#'   p2 = list(long = -122.354, lat = 37.84)
#' )
#' image_size <- define_image_size(bbox, 600)
#' overlay_file <- get_arcgis_map_image(bbox, width = image_size$width,
#'                                      height = image_size$height)
#' 
get_arcgis_map_image <- function(bbox, map_type = "World_Street_Map", file = NULL, 
                                 width = 400, height = 400, sr_bbox = 4326) {
  require(httr)
  require(glue) 
  require(jsonlite)
  
  url <- parse_url("https://utility.arcgisonline.com/arcgis/rest/services/Utilities/PrintingTools/GPServer/Export%20Web%20Map%20Task/execute")
  
  # define JSON query parameter
  web_map_param <- list(
    baseMap = list(
      baseMapLayers = list(
        list(url = jsonlite::unbox(glue("https://services.arcgisonline.com/ArcGIS/rest/services/{map_type}/MapServer",
                                        map_type = map_type)))
      )
    ),
    exportOptions = list(
      outputSize = c(width, height)
    ),
    mapOptions = list(
      extent = list(
        spatialReference = list(wkid = jsonlite::unbox(sr_bbox)),
        xmax = jsonlite::unbox(max(bbox$p1$long, bbox$p2$long)),
        xmin = jsonlite::unbox(min(bbox$p1$long, bbox$p2$long)),
        ymax = jsonlite::unbox(max(bbox$p1$lat, bbox$p2$lat)),
        ymin = jsonlite::unbox(min(bbox$p1$lat, bbox$p2$lat))
      )
    )
  )
  
  res <- GET(
    url, 
    query = list(
      f = "json",
      Format = "PNG32",
      Layout_Template = "MAP_ONLY",
      Web_Map_as_JSON = jsonlite::toJSON(web_map_param))
  )
  
  if (status_code(res) == 200) {
    body <- content(res, type = "application/json")
    message(jsonlite::toJSON(body, auto_unbox = TRUE, pretty = TRUE))
    if (is.null(file)) 
      file <- tempfile("overlay_img", fileext = ".png")
    
    img_res <- GET(body$results[[1]]$value$url)
    img_bin <- content(img_res, "raw")
    writeBin(img_bin, file)
    message(paste("image saved to file:", file))
  } else {
    message(res)
  }
  invisible(file)
}