I'm trying to convert one raster into a SpatialPolygons. I've got a big raster (12 millions pixels) with a lot of zeros, and some negative values (representing some depression in a DEM). I would like to cluster all these negatives values into polygons, to get a map of all the depressions on my map.
I'm a R beginner and I can't find a suitable function to do the job.
Does anyone have a clue ?