development/superseded functions/query_layer_fs.R

In MatthewJWhittle/getarc: An R Wrapper for the ArcGIS Rest API

#' Get Feature Server layer
#'
#' Download feature layer from a feature server
#'
#' @param host url for the ArcGIS Server host e.g 'https://services9.arcgis.com'
#' @param instance a string defining the ArcGIS Server instance
#' @param feature_server a string defining the name of the feature server
#' @param layer_id an integar defining the layer id (starting at 0)
#' @param my_token an access token acquired via \code{get_token}
#' @param query a named vector of parameters to include in the query
#' @param bounding_box an optional bounding box (generated by sf::st_bbox()) to perform a spatial intersects
#' @param crs the output crs, defaulting to 4326
#'
#' @return an sf object
#' @export query_layer_fs
#'
#' @import httr
#' @import sf
#' @importFrom magrittr %>%
query_layer_fs <-
  function(host,
           instance,
           feature_server,
           layer_id = 0,
           query = NULL,
           bounding_box = NULL,
           crs = 4326,
           my_token = NULL) {
    #https://developers.arcgis.com/rest/services-reference/layer-feature-service-.htm

    endpoint <-
      feature_server_endpoint(host,
                              instance,
                              feature_server,
                              layer_id)

    # Get the details of the layer to
    layer_details <- get_layer_details(endpoint = endpoint, my_token = my_token)

    # If a bounding box has been specified then generate the spatial query and combine with the query parameters
    if (!is.null(bounding_box)) {
      query <- c(query, spatial_query_to_list(bbox = bounding_box))
    }

    # Define a named vecotr of default query parameters for returning spatial data
    default_parameters <- c(
      returnIdsOnly = "false",
      # Get all features with sql query 1 = 1
      where = "1=1",
      outFields = "*",
      returnCountOnly = "false",
      f = "json",
      token = NULL,
      # Assert that the data is lat lon if writing to geojson
      outSR = 4326
    )

    default_parameters <-
      default_parameters[!(names(default_parameters) %in% names(query))]
    query <- c(default_parameters, query)

    # Generate the query string
    query_string <- query_string(query = query, my_token = my_token)

    query_url <- paste0(endpoint, "/query", query_string)
    message(paste0("Requesting data:\n", query_url))
    data <- get_geojson(query_url)


    # If the specified crs is not 4326 (the current crs) then transform the data
    if (crs != 4326) {
      data <- data %>% sf::st_transform(crs = crs)
    }

    # Warn if the number of rows in the data is
    if(nrow(data) == layer_details$maxRecordCount){
      warning("May have reached limit of maximum features to return, try performing query to narrow down results.")
    }

    return(data)
  }