Usecase for KML-Parsing: Make New KML-File from File-Collection

In this usecase I had collected several KMLs from the internet but wanted to strip them down for only the relevant parts (the Linestrings inside the Placemark-nodes) and put them all inside one final File. In my script I create a new KML file and populate a folder-node inside it with Linestrings from the collection of KML-files which all reside in the same source directory. For this one needs to parse each file and grab the appropiate nodes and add them to the target kml file. In addition I alter some oroginal values, i.e. I use the file names of the single KML-files as Placemark names inside the new KML-file.

Here is the final file as seen after opening in Google Earth:

library(XML)

# new kml file... needs to be well-formed
z <-
  '<kml xmlns="http://www.opengis.net/kml/2.2">
      <Document>
         <Folder>
            <name>ROUTES</name>
         </Folder>
      </Document>
    </kml>'
new_xmlDoc <- xmlInternalTreeParse(z, useInternalNodes = TRUE)

# important add all namespace definitions...
ns <- c(gx="http://www.google.com/kml/ext/2.2",
        kml="http://www.opengis.net/kml/2.2",
        atom="http://www.w3.org/2005/Atom")
ensureNamespace(new_xmlDoc, ns)

# get the root off the new file for latter processing
new_root <- xmlRoot(new_xmlDoc)

# loop over files from folder
# and insert Placemark content of each file as children nodes into 
# the new file

setwd("C:/Users/Kay/Google Drive/SKI-BIKE/Gastein")
files <- dir(pattern="bergfex*")

for (f in files) { 
   
   # get placemark node of each file
   doc <- xmlInternalTreeParse(f, useInternalNodes = TRUE)
   root <- xmlRoot(doc)
   plcm_node <- root[["Document"]][["Folder"]][["Folder"]][["Placemark"]]

   # insert file name as Placemark name
   xmlValue(plcm_node[["name"]]) <- sub('bergfextour_(.*)[.]kml', '\\1', f)

   # add placemark node to new doc
   addChildren(new_root[["Document"]][["Folder"]], plcm_node)

}

# save it...
saveXML(new_xmlDoc, "collapsed_ROUTES.kml")