terra (version 1.9-25)

merge: Merge SpatRasters, or merge a SpatVector with a data.frame

Description

Merge multiple SpatRasters to create a new SpatRaster with a larger spatial extent. The SpatRasters should all have the same coordinate reference system. They should normally also have the same spatial origin and resolution, but automatic resampling can be done depending on the algorithm used (see argument algo). In areas where the SpatRasters overlap, the values of the SpatRaster that is first in the sequence of arguments (or in the SpatRasterCollection) will be retained (unless first=FALSE).

There is also a method for merging SpatVector with a data.frame; that is, to join the data.frame to the attribute table of the SpatVector.

See classify to merge a SpatRaster with a data.frame.

Usage

# S4 method for SpatRaster,SpatRaster
merge(x, y, ..., first=TRUE, na.rm=TRUE, algo=1, resample=FALSE, method="", 
			filename="", overwrite=FALSE, wopt=list())
# S4 method for SpatRasterCollection,missing
merge(x, first=TRUE, na.rm=TRUE, algo=1, resample=FALSE, method="", filename="", ...)
# S4 method for SpatVector,data.frame
merge(x, y, ...)

Value

SpatRaster or SpatVector

Arguments

x

SpatRaster, SpatRasterCollection, or SpatVector

y

missing if x is a SpatRasterCollection. SpatRaster if x is a SpatRaster. data.frame if x is a SpatVector

...

if x is a SpatRaster: additional objects of the same class as x. If x is a SpatRasterCollection: options for writing files as in writeRaster. If x is a SpatVector, the same arguments as in merge

first

logical. If TRUE, in areas where rasters overlap, the first value is used. Otherwise the last value is used

na.rm

logical. If TRUE missing values are are ignored. This is only used for algo 1; the other two always ignore missing values

algo

integer. You can use 1, 2 or 3 to pick a merge algorithm. algo 1 is generally faster than algo 2, but it may have poorer file compression. Algo 3 creates a virtual raster (see vrt). This is very quick and can be a good approach if the merge raster is used as input to a next step in the analysis. It allows any amount of misalignment and resamples without giving a warning. Otherwise its speed is similar to that of algo 2

resample

logical. If TRUE input rasters are resampled if they do not align (same origin and resolution) with the first raster

method

character. The resampling method used (only if resample is TRUE and algo is 1 or 2). One of "nearest", "bilinear", "cubic", "cubicspline", "lanczos", "average", "mode" as in resample. If the value is "", "nearest" is used for categorical rasters and "bilinear" for other rasters

filename

character. Output filename

overwrite

logical. If TRUE, filename is overwritten

wopt

list with named options for writing files as in writeRaster

See Also

Combining tiles with vrt may be more efficient than using merge.

See mosaic for averaging or blending the values of overlapping regions.

See classify to merge a SpatRaster and a data.frame and union to combine SpatExtent objects.

Examples

x <- rast(xmin=-110, xmax=-80, ymin=40, ymax=70, res=1, vals=1)
y <- rast(xmin=-85, xmax=-55, ymax=60, ymin=30, res=1, vals=2)
z <- rast(xmin=-60, xmax=-30, ymax=50, ymin=20, res=1, vals=3)

m1 <- merge(x, y, z)
m2 <- merge(z, y, x)
m3 <- merge(y, x, z)
# panel(c(m1, m2, m3))

# if you have many SpatRasters, it may be convenient
# to make a SpatRasterCollection
# s <- sprc(list(x, y, z))
s <- sprc(x, y, z)

sm1 <- merge(s, algo=1, first=FALSE)
sm2 <- merge(s, algo=2, first=FALSE)
#sm3 <- merge(s, algo=3, first=FALSE)

## SpatVector with data.frame
f <- system.file("ex/lux.shp", package="terra")
p <- vect(f)
dfr <- data.frame(District=p$NAME_1, Canton=p$NAME_2, Value=round(runif(length(p), 100, 1000)))
dfr <- dfr[1:5, ]
pm <- merge(p, dfr, all.x=TRUE, by.x=c('NAME_1', 'NAME_2'), by.y=c('District', 'Canton'))
pm
values(pm)