fasterize

Fast polygon-to-raster conversion, burn polygon shapes and/or values into pixels.

fasterize is a high-performance replacement for the rasterize() function in the raster package.

Functionality is currently limited to rasterizing polygons in sf-type data frames.

Installation

Install the current version of fasterize from CRAN:

install.packages('fasterize')

Install the development version of fasterize with devtools:

devtools::install_github("ecohealthalliance/fasterize")

fasterize uses Rcpp and thus requires a compile toolchain to install from source. Testing (and for normal use of sf objects) requires sf, which requires GDAL, GEOS, and PROJ to be installed.

Usage

The main function, fasterize(), takes the same inputs as raster::rasterize() but currently has fewer options and is is limited to rasterizing polygons.

A raster() and plot() methods for rasters are re-exported from the raster package.

library(raster)
library(fasterize)
library(wk)
library(fasterize)
p123 <- c(paste0("POLYGON ((-180 -20, -140 55, 10 0, -140 -60, -180 -20),", 
                  "(-150 -20, -100 -10, -110 20, -150 -20))"), 
             "POLYGON ((-10 0, 140 60, 160 0, 140 -55, -10 0))", 
             "POLYGON ((-125 0, 0 60, 40 5, 15 -45, -125 0))")
pols <- data.frame(value = seq_along(p123), geometry = wk::as_wkt(p123))
ex <- as.numeric(wk_bbox(pols))[c(1, 3, 2, 4)]
r <- raster::raster(raster::extent(ex), res = 1)
r <- fasterize(pols, r, field = "value", fun="sum")
plot(r)

Performance

Let’s compare fasterize() to terra::rasterize():

pols_t <- terra::vect(p123)
pols_t$value <- 1:3
#pols_r <-  as(pols_t, "Spatial")
tr <- terra::rast(r)

bench <- microbenchmark::microbenchmark(
 # rasterize = r <- raster::rasterize(pols_r, r, field = "value", fun="sum"),
  terrarize = tr <- terra::rasterize(pols_t, tr, field = "value", fun = "sum"),
  fasterize = f <- fasterize(pols, r, field = "value", fun="sum"),
  unit = "ms"
)

print(bench, digits = 3)

#> Unit: milliseconds
#>       expr   min    lq  mean median    uq   max neval cld
#>  terrarize 22.76 25.13 28.90  25.80 26.85 205.1   100  a 
#>  fasterize  1.83  2.12  2.56   2.46  2.56  19.4   100   b

How does fasterize() do on a large set of polygons? Here I download the IUCN shapefile for the ranges of all terrestrial mammals and generate a 1/6 degree world map of mammalian biodiversity by rasterizing all the layers.

(this doesn’t work anymore because the source data is gone, left as a record 2024-09-25).

if(!dir.exists("Mammals_Terrestrial")) {
  download.file(
    "https://s3.amazonaws.com/hp3-shapefiles/Mammals_Terrestrial.zip",
    destfile = "Mammals_Terrestrial.zip") # <-- 383 MB
  unzip("Mammals_Terrestrial.zip", exdir = ".")
  unlink("Mammals_Terrestrial.zip")
}

mammal_shapes <- st_read("Mammals_Terrestrial")
mammal_raster <- raster(mammal_shapes, res = 1/6)
bench2 <- microbenchmark::microbenchmark(
  mammals = mammal_raster <- fasterize(mammal_shapes, mammal_raster, fun="sum"),
  times=20, unit = "s")
print(bench2, digits=3)
par(mar=c(0,0.5,0,0.5))
plot(mammal_raster, axes=FALSE, box=FALSE)

#> Unit: seconds
#>     expr   min    lq  mean median    uq   max neval
#>  mammals 0.847 0.857 0.883  0.886 0.894 0.963    20

About

fasterize was developed openly at EcoHealth Alliance under the USAID PREDICT project.
In Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.