I have a rather large raster (384 MB) that I am trying to convert to a polygon shapefile in R.
The rastertoPolygons function from the raster package doesn't seem to be able to handle this, as I tried running it but gave up after it was going for 7+ hours.
I also tried to use gdal_polygonize.py from GDAL in python via this function by John Baumgartner but after letting the function run for 30+ minutes I still have nothing. Am I simply not letting it run long enough? I was under the impression that gdal_polyonize.py was supposed to be very quick, i.e. seconds.
Here's a link to my raster file.
Any guidance would be greatly appreciated.
terra does this much faster than raster (but not faster than GDAL because that is what it uses)
library(terra)
r <- rast("top6loss.tif")
Note that you have 22 billion cells (that is a lot by most standards, and that is why it takes a while):
ncell(r)
#[1] 21989436765
It finishes in 10 minutes on my laptop
system.time(p <- as.polygons(r))
# user system elapsed
# 562.34 3.54 568.77
p
#class : SpatVector
#geometry : polygons
#dimensions : 6, 1 (geometries, attributes)
#extent : -13.54777, 12.33558, -6.134633, 9.781491 (xmin, xmax, ymin, ymax)
#coord. ref. : +proj=longlat +datum=WGS84 +no_defs
These are the 6 values
as.data.frame(p)
# top6loss
#1 2254
#2 5418
#3 13623
#4 14344
#5 15885
#6 19654
You can save the file with
writeVector(p, "cells.shp")