raster (version 2.1-41)

rasterize: Rasterize points, lines, or polygons

Description

Transfer values associated with 'object' type spatial data (points, lines, polygons) to raster cells. For polygons, values are transferred if the polygon covers the center of a raster cell. For lines, values are transferred to all cells that are touched by a line. You can combine this behaviour by rasterizing polygons as lines first and then as polygons. If x represents points, each point is assigned to a grid cell. Points that fall on a border between cells are placed in the cell to the right and/or in the cell below. The value of a grid cell is determined by the values associated with the points and function fun.

Usage

## S3 method for class 'matrix,Raster':
rasterize(x, y, field, fun='last', background=NA,
     mask=FALSE, update=FALSE, updateValue='all', filename="", na.rm=TRUE, ...)
	
## S3 method for class 'SpatialPoints,Raster':
rasterize(x, y, field, fun='last', background=NA, 
    mask=FALSE, update=FALSE, updateValue='all', filename="", na.rm=TRUE, ...)
	
## S3 method for class 'SpatialLines,Raster':
rasterize(x, y, field, fun='last', background=NA, 
    mask=FALSE, update=FALSE, updateValue='all', filename="", ...)
	
## S3 method for class 'SpatialPolygons,Raster':
rasterize(x, y, field, fun='last', background=NA, 
    mask=FALSE, update=FALSE, updateValue='all', filename="", 
    getCover=FALSE, silent=FALSE, ...)

Arguments

x

points (a SpatialPoints* object, or a two-column matrix (or data.frame)), SpatialLines*, SpatialPolygons*, or an Extent object

y

Raster* object

field

numeric or character. The value(s) to be transferred. This can be a single number, or a vector of numbers that has the same length as the number of spatial features (points, lines, polygons). If x is a Spatial*DataFrame, this can be the colum

fun

function or character. To determine what values to assign to cells that are covered by multiple spatial features. You can use functions such as min, max, or mean, or one of the following character values: 'first',

background

numeric. Value to put in the cells that are not covered by any of the features of x. Default is NA

mask

logical. If TRUE the values of the input Raster object are 'masked' by the spatial features of x. That is, cells that spatially overlap with the spatial features retain their values, the other cells become NA. Defaul

update

logical. If TRUE, the values of the Raster* object are updated for the cells that overlap the spatial features of x. Default is FALSE. Cannot be used when mask=TRUE

updateValue

numeric (normally an integer), or character. Only relevant when update=TRUE. Select, by their values, the cells to be updated with the values of the spatial features. Valid character values are 'all', 'NA', and

filename

character. Output filename (optional)

na.rm

If TRUE, NA values are removed if fun honors the na.rm argument

getCover

logical. If TRUE, the fraction of each grid cell that is covered by the polygons is returned (and the values of field, fun, mask, and update are ignored. The fraction covered is estimated by dividing each cell into 1

silent

Logical. If TRUE, feedback on the polygon count is suppressed. Default is FALSE

...

Additional arguments for file writing as for writeRaster

Value

• RasterLayer or RasterBrick

See Also

extract

Examples

###############################
# rasterize points
###############################
r <- raster(ncols=36, nrows=18)
n <- 1000
x <- runif(n) * 360 - 180
y <- runif(n) * 180 - 90
xy <- cbind(x, y)
# get the (last) indices
r0 <- rasterize(xy, r)
# prensence/absensce (NA) (is there a point or not?)
r1 <- rasterize(xy, r, field=1)
# how many points?
r2 <- rasterize(xy, r, fun=function(x,...)length(x))
vals <- runif(n)
# sum of the values associated with the points
r3 <- rasterize(xy, r, vals, fun=sum)

# with a SpatialPointsDataFrame
vals <- 1:n
p <- data.frame(xy, name=vals)
coordinates(p) <- ~x+y
r <- rasterize(p, r, 'name', fun=min)
#r2 <- rasterize(p, r, 'name', fun=max)
#plot(r, r2, cex=0.5)

###############################
# rasterize lines
###############################
cds1 <- rbind(c(-180,-20), c(-140,55), c(10, 0), c(-140,-60))
cds2 <- rbind(c(-10,0), c(140,60), c(160,0), c(140,-55))
cds3 <- rbind(c(-125,0), c(0,60), c(40,5), c(15,-45))

lines <- SpatialLines(list(Lines(list(Line(cds1)), "1"), 
     Lines(list(Line(cds2)), "2"), Lines(list(Line(cds3)), "3") ))

r <- raster(ncols=90, nrows=45)
r <- rasterize(lines, r)

plot(r)
plot(lines, add=TRUE)

r <- rasterize(lines, r, fun='count')
plot(r)

r[] <- 1:ncell(r)
r <- rasterize(lines, r, mask=TRUE)
plot(r)

r[] <- 1
r[lines] <- 10
plot(r)

###############################
# rasterize polygons
###############################

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))
p2 <- rbind(c(-10,0), c(140,60), c(160,0), c(140,-55), c(-10,0))
p3 <- rbind(c(-125,0), c(0,60), c(40,5), c(15,-45), c(-125,0))
pols <- SpatialPolygons( list(  Polygons(list(Polygon(p1), Polygon(hole)), 1),
      Polygons(list(Polygon(p2)), 2), Polygons(list(Polygon(p3)), 3)))
pols@polygons[[1]]@Polygons[[2]]@hole <- TRUE

r <- raster(ncol=180, nrow=90)
r <- rasterize(pols, r, fun='sum')


plot(r)
plot(pols, add=T)

# add a polygon
p5 <- rbind(c(-180,10), c(0,90), c(40,90), c(145,-10),  
            c(-25, -15), c(-180,0), c(-180,10))
addpoly <- SpatialPolygons(list(Polygons(list(Polygon(p5)), 1)))
addpoly <- as(addpoly, "SpatialPolygonsDataFrame")
addpoly@data[1,1] <- 10
r2 <- rasterize(addpoly, r, field=1, update=TRUE, updateValue="NA")
plot(r2)
plot(pols, border="blue", lwd=2, add=TRUE)
plot(addpoly, add=TRUE, border="red", lwd=2)

# get the percentage cover of polygons in a cell
r3 <- raster(ncol=36, nrow=18)
r3 <- rasterize(pols, r3, getCover=TRUE)