Use Case: Make Contour Lines for Google Earth with Spatial R

Here's comes a script I wrote for creating contour lines in KML-format to be used with Google Earth https://github.com/gimoya/theBioBucket-Archives/blob/master/R/r_contours_for_google_earth.R

If you want to check or just use the datasets I created for the Alps region, you can download it here: http://terrain-overlays.blogspot.co.at/index.html

Use GDAL from R Console to Split Raster into Tiles

When working with raster datasets I often encounter performance issues caused by the large filesizes. I thus wrote up a little R function that invokes gdal_translate which would split the raster into parts which makes subsequent processing more CPU friendly. I didn't use built-in R functions simply because performance is much better when using gdal from the command line..

The screenshot to the left shows a raster in QGIS that was split into four parts with the below script.

## get filesnames (assuming the datasets were downloaded already. 
## please see http://thebiobucket.blogspot.co.at/2013/06/use-r-to-bulk-download-digital.html 
## on how to download high-resolution DEMs)
setwd("D:/GIS_DataBase/DEM")
files <- dir(pattern = ".hgt")

## function for single file processing mind to replace the PATH to gdalinfo.exe!
## s = division applied to each side of raster, i.e. s = 2 gives 4 tiles, 3 gives 9, etc.
split_raster <- function(file, s = 2) {
    
    filename <- gsub(".hgt", "", file)
    gdalinfo_str <- paste0("\"C:/OSGeo4W64/bin/gdalinfo.exe\" ", file)
      
    # pick size of each side
    x <- as.numeric(gsub("[^0-9]", "", unlist(strsplit(system(gdalinfo_str, intern = T)[3], ", "))))[1]
    y <- as.numeric(gsub("[^0-9]", "", unlist(strsplit(system(gdalinfo_str, intern = T)[3], ", "))))[2]
    
    # t is nr. of iterations per side
    t <- s - 1
    for (i in 0:t) {
        for (j in 0:t) {
            # [-srcwin xoff yoff xsize ysize] src_dataset dst_dataset
            srcwin_str <- paste("-srcwin ", i * x/s, j * y/s, x/s, y/s)
            gdal_str <- paste0("\"C:/OSGeo4W64/bin/gdal_translate.exe\" ", srcwin_str, " ", "\"", file, "\" ", "\"", filename, "_", i, "_", j, ".tif\"")
            system(gdal_str)
        }
    }
}

## process all files and save to same directory
mapply(split_raster, files, 2) 

Use Case: Spatial R & Google Earth for Terrain Analyses

I'd like to share code that uses spatial R and Google Earth for terrain analyses. In this example I took SRTM data at 1" resolution from http://www.viewfinderpanoramas.org/dem3.html#alps read it into R did a little processing and finally wrapped it up in a KML-file that I use as ground-overlay in Google Earth. In fact I eventually converted it into a sqlitedb with MAPC2MAPC for usage on a mobile device.

See the code here on github..