# R GIS: Generalizer for KML Paths

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I’m posting a recent project’s spin-off, which is a custom line-generalizer which I used for huge KML-paths. Anyone with a less clumpsy approach?**theBioBucket***, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

## line generalizing function: takes two vectors of with x/ycoords ## and return ids of x/y elements which distance to its next element ## is shorter than the average distance between consecutive vertices ## multiplied by 'fac' check_dist <- function(x, y, fac) { dm <- as.matrix(dist(cbind(x, y))) ## supradiagonal holds distance from 1st to 2nd, 2nd to 3rd, etc. element d <- diag(dm[-1, -ncol(dm)]) mean_dist <- mean(d) keep <- logical() ## allways keep first.. keep[1] <- T for (i in 1:(length(x) - 2)) { keep[i + 1] <- (d[i] > mean_dist * fac) message(paste0("Distance from item ", i, " to item ", i + 1, " is: ", d[i])) } message(paste0("Treshold is: ", mean_dist * fac)) cat("--\n") ## .. and always keep last keep[length(x)] <- T return(keep) } ## Testing function check_dist: x <- rnorm(5) y <- rnorm(5) (keep <- check_dist(x, y, 1.2)) plot(x, y) lines(x[keep], y[keep], lwd = 4, col = "green") lines(x, y, lwd = 1, col = "red") text(x, y + 0.1, labels = c(1:length(x))) ## exclude vertices by generalization rule. coordinate-nodes with low number of vertices, ## segments with less than 'min_for_gen' vertices will not be simplified, in any case coordinates will be ## rounded to 5-th decimal place generalize_kml_contour_node <- function(node, min_for_gen, fac) { require(XML) LineString <- xmlValue(node, trim = T) LineStrSplit <- strsplit(unlist(strsplit(LineString, "\\s")), ",") # filter out empty LineStrings which result from strsplit on '\\s' LineStrSplit <- LineStrSplit[sapply(LineStrSplit, length) > 0] # all 3 values are required, in case of error see for missing z-values: x <- round(as.numeric(sapply(LineStrSplit, "[[", 1, simplify = T)), 5) y <- round(as.numeric(sapply(LineStrSplit, "[[", 2, simplify = T)), 5) z <- round(as.numeric(sapply(LineStrSplit, "[[", 3, simplify = T)), 5) # for lines longer than 'min_for_gen' vertices, generalize LineStrings if (length(x) >= min_for_gen) { keep <- check_dist(x, y, fac) x <- x[keep] y <- y[keep] z <- z[keep] xmlValue(node) <- paste(paste(x, y, z, sep = ","), collapse = " ") # for all other cases, insert rounded values } else { xmlValue(node) <- paste(paste(x, y, z, sep = ","), collapse = " ") } } ## mind to use the appropiate namespace definition: alternatively use: ## c(kml ='http://opengis.net/kml/2.2') kml_generalize <- function(kml_file, min_for_gen, fac) { doc <- xmlInternalTreeParse(kml_file) nodes <- getNodeSet(doc, "//kml:LineString//kml:coordinates", c(kml = "http://earth.google.com/kml/2.0")) mapply(generalize_kml_contour_node, nodes, min_for_gen, fac) saveXML(doc, paste0(dirname(kml_file), "/simpl_", basename(kml_file))) } ## get KML-files and generalize them kml_file <- tempfile(fileext = ".kml") download.file("http://dev.openlayers.org/releases/OpenLayers-2.13.1/examples/kml/lines.kml", kml_file, mode = "wb") kml_generalize(kml_file, 5, 0.9) shell.exec(kml_file) shell.exec(paste0(dirname(kml_file), "/simpl_", basename(kml_file)))

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