Exercise in grImport

Last week I used grImport for the first time. I decided to try perform another exercise using it. The task was to add voivodeship division of Poland.

Standard R maps do not contain such a division. I have found it on r-forge in package  mapoland based on ESRI shape files, but I wanted to import such a map from SVG file which can be found on Wikipedia. As last time SVG file has to be converted do PS first. Here is a comparison of both maps showing that the import worked quite well.

And this is the code I have used:

library(grImport)

PostScriptTrace("Wojewodztwa.ps")

voiv <- readPicture("Wojewodztwa.ps.xml")

broken.voiv <- explodePaths(voiv)

#extracting voivodeship 'PictureStrokes'

xpath <- ypath <- list()

sel <- c(2,4,6,8,20,22,24,28,30,32,34,36,38,41,44,46)

for (i in seq(along = sel)) {

      xpath[[i]] <- broken.voiv[[sel[i]]]@paths$path@x

      ypath[[i]] <- broken.voiv[[sel[i]]]@paths$path@y

}

#adding Wolin island to zachodniopomorskie

xpath[[2]] <- c(broken.voiv[10]@paths$path@x[c(39:1, 95:40)],

                xpath[[2]])

ypath[[2]] <- c(broken.voiv[10]@paths$path@y[c(39:1, 95:40)],

                ypath[[2]])

library(mapoland)

pl <- getShape("voiv")

#functions rescaling paths to mapoland map size

transx <- function(x) {

      old <- c(min(sapply(xpath,min)), max(sapply(xpath,max)))

      new <- pl@bbox[1,]

      ((x - old[1]) / (old[2] - old[1])) * (new[2] - new[1])

    + new[1]

}

transy <- function(y) {

      old <- c(min(sapply(ypath, min)), max(sapply(ypath, max)))

      new <- pl@bbox[2,]

      ((y - old[1]) / (old[2] - old[1])) * (new[2] - new[1])

    + new[1]

}

plot(pl, lwd = 4)

for (i in seq(along = sel)) {

      lines(transx(xpath[[i]]), transy(ypath[[i]]), col = "red")

}