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It’s the result of a conversion of a polygon shapefile of country boundaries (from Natural Earth, a great source of public domain, physical/cultural spatial data) to a raster data set.
Convert raster to vector in r code#
The function included below ( gdal_polygonizeR) borrows from code provided in a post by Lyndon Estes on R-sig-geo. usr/bin).Īnywho… let’s compare rasterToPolygons with gdal_polygonize. I suspect Linux users should typically not run into this problem, as the GDAL executables are usually installed to paths that already exist in PATH (e.g. The PATH variable can be modified by following these instructions for Windows and Mac. In the latter case, you can either use the pypath argument accepted by the function below to specify the path, or modify your PATH variable. If this returns an empty string, it looks like gdal_polygonize.py either doesn’t exist on your system, or the path to its containing directoy is missing from the PATH variable. To check if this is the case, run the following in R: Finally, it helps if the path to the gdal_polygonize.py exists in the global PATH variable. For polygonize and a couple of others, you’ll also need Python installed (again, you may already have it installed, so check first!). Once installed, you have at your disposal a bunch of GDAL Utilities that can be run from the terminal, including gdal_polygonize.py. Together with it’s cousin OGR, GDAL allows reading and writing of a wide range of raster and vector geospatial data formats.
Convert raster to vector in r software#
GDAL needs to be installed on your system, but you’ll probably want it installed anyway if you’re planning to talk to spatial data (in fact, you might find you actually already have it installed, as it is required for a bunch of other GIS software packages). We can cut down the time taken for conversion by calling a GDAL utility, gdal_polygonize.py, directly from R using system2(). The fantastic raster package has a function that can do this ( rasterToPolygons), but it seems to take a very, very long time and chew up all system resources (at least on my not particularly souped up X200 laptop). I like to keep my code together so I can easily keep track of what I’ve done, so it made sense to do the conversion in R as well. Today I needed to convert a raster to a polygon shapefile for further processing and plotting in R.