Raster-polygon_extraction.r

# Download and analyse precipitation data for a polygon

# Libraries
library(raster)
library(sf)
library(rgdal)
library(utils) # For download.file

setwd("~/Downloads")

# Download and unarchive the file
download.file(url = "https://data.chc.ucsb.edu/products/CHIRPS-2.0/africa_monthly/bils/v2p0chirps202105.tar.gz",
              destfile = "v2p0chirps202105.tar.gz", method = "auto")
untar("v2p0chirps202105.tar.gz")

# Load the raster and set NA values
r <- raster("v2p0chirps202105.bil", crs = "+proj=longlat +datum=WGS84")
values(r)[values(r) == -9999] <- NA # NA values

# Load the shapefile and convert to WGS84 lat/lon
p <- read_sf("Uluguru/Uluguru_disso.shp")
p <- st_transform(p, crs = 4326)

# Extract the values 
p.mean <- extract(r, st_zm(p), fun = mean) 
p.min <- extract(r, st_zm(p), fun = min)
p.max <- extract(r, st_zm(p), fun = max)