fasterize: Rasterize an sf object of polygons

Description

Rasterize set of polygons

Fast sf-to-raster conversion

Usage

fasterize(
  sf,
  raster,
  field = NULL,
  fun = "last",
  background = NA_real_,
  by = NULL
)

Value

A raster of the same size, extent, resolution and projection as the provided raster template.

Arguments

sf: an sf::sf() object with a geometry column of POLYGON and/or MULTIPOLYGON objects.
raster: A raster object. Used as a template for the raster output. Can be created with raster::raster(). The fasterize package provides a method to create a raster object from an sf object.
field: character. The name of a column in sf, providing a value for each of the polygons rasterized. If NULL (default), all polygons will be given a value of 1.
fun: character. The name of a function by which to combine overlapping polygons. Currently takes "sum", "first", "last", "min", "max", "count", or "any". Future versions may include more functions or the ability to pass custom R/C++ functions. If you need to summarize by a different function, use by= to get a RasterBrick and then raster::stackApply() or raster::calc() to summarize.
background: numeric. Value to put in the cells that are not covered by any of the features of x. Default is NA.
by: character. The name of a column in sf by which to aggregate layers. If set, fasterize will return a RasterBrick with as many layers as unique values of the by column.

Details

This is a high-performance replacement for raster::rasterize().

The algorithm is based on the method described in course materials provided by Wayne O. Cochran. The algorithm is originally attributed to Wylie et al. (1967).

References

Wylie, C., Romney, G., Evans, D., & Erdahl, A. (1967). Half-tone perspective drawings by computer. Proceedings of the November 14-16, 1967, Fall Joint Computer Conference. AFIPS '67 (Fall). https://dx.doi.org/10.1145/1465611.1465619

Examples

Run this code

library(sf)
library(fasterize)
p1 <- rbind(c(-180,-20), c(-140,55), c(10, 0), c(-140,-60), c(-180,-20))
hole <- rbind(c(-150,-20), c(-100,-10), c(-110,20), c(-150,-20))
p1 <- list(p1, hole)
p2 <- list(rbind(c(-10,0), c(140,60), c(160,0), c(140,-55), c(-10,0)))
p3 <- list(rbind(c(-125,0), c(0,60), c(40,5), c(15,-45), c(-125,0)))
pols <- st_sf(value = rep(1,3),
              geometry = st_sfc(lapply(list(p1, p2, p3), st_polygon)))
r <- raster(pols, res = 1)
r <- fasterize(pols, r, field = "value", fun="sum")
plot(r)

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