Zonal statistics

Compute zonal statistics, that is summarize values of a SpatRaster for each "zone" defined by another SpatRaster, or by a SpatVector with polygon geometry.

If fun is a true R function, the <SpatRaster,SpatRaster> method may fail when using very large SpatRasters, except for the functions ("mean", "min", "max", "sum", "isNA", and "notNA").

You can also summarize values of a SpatVector for each polygon (zone) defined by another SpatVector.

# S4 method for SpatRaster,SpatRaster
zonal(x, z, fun="mean", ..., w=NULL, wide=TRUE,
    as.raster=FALSE, filename="", overwrite=FALSE, wopt=list())

# S4 method for SpatRaster,SpatVector
zonal(x, z, fun=mean, ..., w=NULL, weights=FALSE,
    exact=FALSE, touches=FALSE, as.raster=FALSE, filename="", wopt=list())

# S4 method for SpatVector,SpatVector
zonal(x, z, fun=mean, ..., weighted=FALSE, as.polygons=FALSE)

Arguments

x: SpatRaster or SpatVector
z: SpatRaster with cell-values representing zones or a SpatVector with each polygon geometry representing a zone. z can have multiple layers to define intersecting zones
fun: function to be applied to summarize the values by zone. Either as character: "mean", "min", "max", "sum", "isNA", and "notNA" and, for relatively small SpatRasters, a proper function
...: additional arguments passed to fun, such as na.rm=TRUE
w: SpatRaster with weights. Should have a single-layer with non-negative values
wide: logical. Should the values returned in a wide format? This only affects the results when nlyr(z) == 2
as.raster: logical. If TRUE, a SpatRaster is returned with the zonal statistic for each zone
filename: character. Output filename (ignored if as.raster=FALSE
overwrite: logical. If TRUE, filename is overwritten
wopt: list with additional arguments for writing files as in writeRaster
weights: logical. If TRUE and y has polygons, the approximate fraction of each cell that is covered is returned as well, for example to compute a weighted mean
exact: logical. If TRUE and y has polygons, the exact fraction of each cell that is covered is returned as well, for example to compute a weighted mean
touches: logical. If TRUE, values for all cells touched by lines or polygons are extracted, not just those on the line render path, or whose center point is within the polygon. Not relevant for points; and always considered TRUE when weights=TRUE or exact=TRUE
weighted: logical. If TRUE, a weighted.mean is computed and fun is ignored. Weights are based on the length of the lines or the area of the polygons in x that intersect with z. This argument is ignored of x is a SpatVector or points
as.polygons: logical. Should the results be merged with the attributes of z?

Value

A data.frame with a value for each zone, or a SpatRaster, or SpatVector of polygons.

Examples


### SpatRaster, SpatRaster
r <- rast(ncols=10, nrows=10)
values(r) <- 1:ncell(r)
z <- rast(r)
values(z) <- rep(c(1:2, NA, 3:4), each=20)
names(z) <- "zone"
zonal(r, z, "sum", na.rm=TRUE)
#>   zone lyr.1
#> 1    1   210
#> 2    2   610
#> 3    3  1410
#> 4    4  1810

# with weights 
w <- init(r, "col")
zonal(r, z, w=w, "mean", na.rm=TRUE)
#>   zone lyr.1
#> 1    1    12
#> 2    2    32
#> 3    3    72
#> 4    4    92

# multiple layers
r <- rast(system.file("ex/logo.tif", package = "terra")) 
# zonal layer 
z <- rast(r, 1)
names(z) <- "zone"
values(z) <- rep(c(1:2, NA, c(3:4)), each=ncell(r)/5, length.out=ncell(r))

zonal(r, z, "mean", na.rm = TRUE)
#>   zone      red    green     blue
#> 1    1 197.9486 198.0103 193.5556
#> 2    2 173.2219 176.7717 185.2585
#> 3    3 168.2952 172.6232 184.6939
#> 4    4 193.5859 197.0019 206.5717

# raster of zonal values
zr <- zonal(r, z, "mean", na.rm = TRUE, as.raster=TRUE)


### SpatRaster, SpatVector
x <- rast(ncol=2,nrow=2, vals=1:4, xmin=0, xmax=1, ymin=0, ymax=1, crs="+proj=utm +zone=1")
p <- as.polygons(x)
pp <- shift(p, .2)
r <- disagg(x, 4)

zonal(r, p)
#>   lyr.1
#> 1     1
#> 2     2
#> 3     3
#> 4     4
zonal(r, p, sum)
#>   lyr.1
#> 1    16
#> 2    32
#> 3    48
#> 4    64
zonal(x, pp, exact=TRUE)
#>   lyr.1
#> 1   1.4
#> 2   2.0
#> 3   3.4
#> 4   4.0
zonal(c(x, x*10), pp, w=x)
#>   lyr.1 lyr.1
#> 1     1    10
#> 2     2    20
#> 3     3    30
#> 4     4    40


### SpatVector, SpatVector

f <- system.file("ex/lux.shp", package="terra")
v <- vect(f)[,c(2,4)]

p <- spatSample(v, 100)
values(p) <- data.frame(b2=1:100, ssep1=100:1)

zonal(p, v, mean)
#>    zone       b2    ssep1
#> 1     1 49.40000 51.60000
#> 2     2 51.66667 49.33333
#> 3     3 48.00000 53.00000
#> 4     4 34.00000 67.00000
#> 5     5 66.30769 34.69231
#> 6     6 53.33333 47.66667
#> 7     7 29.80000 71.20000
#> 8     8 41.60000 59.40000
#> 9     9 47.33333 53.66667
#> 10   10 45.37500 55.62500
#> 11   11 55.20000 45.80000
#> 12   12 55.15385 45.84615

Arguments

Value

See also

Examples