我写了一个小函数来反转KML线串中坐标的排序。但是,我遇到了一个具有不同名称空间定义的问题,并帮助自己解决了一个相当笨拙的解决方法。
编辑:显然,KML周围有几种不同的命名空间定义。下面我检查两个我知道的替代方案,但也许这只是一个肮脏的修复,并且有更好的方法来处理KML的不同命名空间?
## name: ReverseKmlPath
## use: Reverser a KML-path by matching its
## arguments: PATH_TO_DOC the path to the KML-file
## NAME the value of the name tag, function uses partial matching!
## 'Trail_xyz' will be matched by 'Trail'
## requirements: KML-structure with Placemarks containing a <name> and a <coordinates> tag
## author: Kay Cichini
## date: 01-05-2014
## license: CC-BY-NC-SA
ReverseKmlPath <- function(PATH_TO_DOC, NAMES) {
require(XML)
doc <- xmlInternalTreeParse(PATH_TO_DOC)
if (xmlNamespaceDefinitions(doc)[[1]]$uri == "http://www.opengis.net/kml/2.2") {
namespaces <- c(kml = "http://www.opengis.net/kml/2.2")
flag <- 1
} else {
if (xmlNamespaceDefinitions(doc)[[1]]$uri == "http://earth.google.com/kml/2.0") {
namespaces <- c(kml0 = "http://earth.google.com/kml/2.0")
flag <- 0
} else {
stop ("Stopped!: Check namespace issue..")
}
}
for (NAME in NAMES) {
if (flag) {
query <- paste0("//kml:Placemark[contains(kml:name,'", sprintf("%s", NAME), "'", ")]//kml:coordinates")
} else {
query <- paste0("//kml0:Placemark[contains(kml0:name,'", sprintf("%s", NAME), "'", ")]//kml0:coordinates")
}
coords <- tryCatch(getNodeSet(doc, query, namespaces),
error = function(e) message(paste("\nError: *", NAME, "* was NOT successfully matched\n")))
for (i in length(coords)) {
#grab coordinates from node and reverse order
rev_coord_vector <- rev(unlist(strsplit(gsub("\\t|\\n", "", xmlValue(coords[[i]])), "\\s")))
rev_coord_string <- paste(rev_coord_vector, collapse = " ")
# re-insert reversed line-string:
xmlValue(coords[[i]]) <- rev_coord_string
# message
if (flag) {
query <- paste0("//kml:Placemark[contains(kml:name,'", sprintf("%s", NAME), "'", ")]//kml:name")
} else {
query <- paste0("//kml0:Placemark[contains(kml0:name,'", sprintf("%s", NAME), "'", ")]//kml0:name")
}
match <- xmlValue(getNodeSet(doc, query, namespaces)[[i]])
message(paste0("matched name: ", match, "\n..."))
}
}
# save:
message("Reversed paths saved to:")
saveXML(doc, paste0(dirname(PATH_TO_DOC), "/reversed_", basename(PATH_TO_DOC)),
prefix = newXMLCommentNode("This file was created with the R-package XML::saveXML, see: "))
}
## not run:
tf <- tempfile(fileext = ".kml")
download.file("http://dev.openlayers.org/releases/OpenLayers-2.13.1/examples/kml/lines.kml", tf, mode = "wb")
ReverseKmlPath( PATH_TO_DOC = tf, NAMES = c("Absolute", "Relative") )
shell.exec(tf)
shell.exec(paste0(dirname(tf), "/reversed_", basename(tf)))