[R-sig-Geo] Extract function - too much data for R?

[GD]

I had related situation with 85000 non-overlapping polygons, and a raster
dataset with dimensions ~ 10000x10000. In that case I wanted the full
distribution of pixel values inside each polygon, rather than just the mean.

An efficient approach (much faster than extract) was:

1) Rasterize the polygons (to a single raster with the same dimensions as
the input raster dataset). My polygons had a unique ID value that was burned
into the raster. I did this with 'gdal_rasterize'

2) Use the 'crosstab' function in the 'raster' package to cross-tabulate the
values from the ID raster with the values on the input raster dataset. This
gives the full range of pixel values associated with each polygon ID.

3) From there, it is straightforward to apply whichever function to the
pixel values for each ID.




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