R/extract_osm_nodes.R

In Japhilko/gosmd: Access OpenStreetMap Data

#' Function extract_osm_nodes
#'
#' @description Extract a dataframe from XML OpenStreetMap data
#' @param OSM.Data an osm object
#' @param value a map feature
#'
#' @author Jan-Philipp Kolb <Jan-Philipp_Kolb@gmx.net>
#' @return A dataframe
#' @references \url{http://wiki.openstreetmap.org/wiki/Map_Features}
#' @examples
#' \donttest{
#' schools <- get_osm_nodes(object='amenity=school',place='Heidelberg')
#' info <- extract_osm_nodes(OSM.Data=schools,value='school')
#' }
#' @importFrom XML xpathApply
#' @export
extract_osm_nodes <- function(OSM.Data,value){
  node_id<- xpathApply(OSM.Data,paste("//tag[@v= '",value,"']/parent::node/@ id",sep="") )
  if(length(node_id)>0){
    lat_x <- xpathApply(OSM.Data,paste("//tag[@v = '",value,"']/parent::node/@ lat",sep=""))
    lon_x <- xpathApply(OSM.Data,paste("//tag[@v = '",value,"']/parent::node/@ lon",sep=""))
    Liste <- list()
    if (length(node_id)>5000){cat("It can take some time!","\n")}
    for (i in 1:length(node_id)){
      Liste_i <- unlist(xpathApply(OSM.Data,paste("//node[@id = ",node_id[i],"]//tag/attribute::*",sep="")))
      ind_k <- which(names(Liste_i)=="k")
      ind_v <- which(names(Liste_i)=="v")
      Liste[[i]] <- data.frame(k=Liste_i[ind_k],
                             v=Liste_i[ind_v],
                             id=rep(unlist(node_id[i]),length(ind_k))
      )
    }
    DF_x <- do.call(rbind,Liste)
    DF_x1 <- data.frame(with(DF_x,tapply(v,list(id,k),function(x)as.character(x))))
    if(length(lat_x)>0){
      DF_x1$lat <- unlist(as.numeric(lat_x))
      DF_x1$lon <- unlist(as.numeric(lon_x))
    }
    return(DF_x1)
  }else{cat("No objects found","\n")}
}