0

I'm extracting values for some coordinates from rasters using raster package. I'm planning to use a buffer of 1km to do the extraction. But it seems impossible using extract function in terra pakcage.

Much appreciated if you can help me out.

user3374236
  • 57
  • 7
  • I would highly recommend to add an example data set and possibly a code to start with to solve this question. What's your pixel resolution? Also have a look at the native raster buffer function: https://www.rdocumentation.org/packages/raster/versions/3.4-13/topics/buffer – benschbob91 Aug 08 '21 at 04:35

1 Answers1

3

Just convert the coordinates to points and then create a buffer around them Here a benchmarck with different packages:

library(terra)
library(raster)
library(exactextractr)
library(sf)
#create example raster
r <- raster(ncol=36, nrow=18, vals=1:(18*36))

# extract values with coordinates (converted to points)
#create some coordinates
xy <- cbind(-50, seq(-80, 80, by=20))
#convert to points
sp <- SpatialPoints(xy)
#create a buffer around the points
sp_buffer <-st_buffer(st_as_sf(sp),20) 


#extract ----------------------------------------------------------------
#raster
raster::extract(r, sp_buffer)
#terra
terra::extract(r, sp_buffer)
#exactextract
exactextractr::exact_extract(r,sp_buffer)

library(microbenchmark)
microbenchmark(raster=raster::extract(r, sp_buffer),
               terra=terra::extract(r, sp_buffer),
               exactextract=exactextractr::exact_extract(r,sp_buffer)
)

Unit: milliseconds
         expr     min       lq      mean   median       uq      max neval cld
       raster 56.0899 59.19100 65.547358 60.64650 62.12665 300.6713   100   b
        terra 56.3695 58.90810 65.549521 60.47245 62.22330 179.3679   100   b
 exactextract  8.0596  8.53215  9.447963  8.71500  8.91085  81.8115   100  a

as you can see exact_extract is the fastest function for extracting values from polygons (7 time faster)

Elia
  • 2,210
  • 1
  • 6
  • 18