Extract values from raster using point data with buffer in R

Question

I'm little bit worried, because of this:

satellite_buffered <- raster::extract(satellite_raster, hila_FI_WGS84, buffer=7000)

If buffer is in meters the code works, but if I use degrees, it won't. Using degrees I will get only one raster value to each point. Raster is 0.05 degree grid and originally point data is 10km*10km grid (metric projection ETRS-TM35FIN and after transformation to lat/lon it is not any more a regular grid)

Data structures:

str(satellite_raster) Formal class '.RasterFile' [package "raster"] with 13 slots

@ projargs: chr "+init=epsg:4326 +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0"

and str(hila_FI_WGS84) Formal class 'SpatialPointsDataFrame' [package "sp"] with 5 slots

@ projargs: chr "+init=epsg:4326 +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0"

Answer 1

If buffer is in meters the code works, but if I use degrees, it won't.

Indeed; the buffer cannot be specified in degrees. ?extract, buffer says: "If the data are not projected (latitude/longitude), the unit should be meters. Otherwise it should be in map-units (typically also meters)."

Do you really want the buffer to be in degrees?

Is so, temporarily set the CRS to UTM, do the extract, and set it back.

cr <- crs(r)
crs(r) <- '+proj=utm +zone=10 +datum=WGS84'
e <- extract(r, xy, buffer=0.5)
crs(r) <- cr