terra (version 1.9-25)

update: Update a raster file

Description

Update metadata or cell values of a file that is the data source of a SpatRaster. This modifies the file on disk directly without reading the entire raster into memory.

BE CAREFUL with this function as you are overwriting data in an existing file.

Usage

# S4 method for SpatRaster
update(object, crs=FALSE, extent=FALSE, names=FALSE,
    cells=NULL, values=NULL, layer=0)

Value

SpatRaster (invisibly)

Arguments

object

SpatRaster with a file source

crs

logical. Should the coordinate reference system be updated?

extent

logical. Should the extent be updated?

names

logical. Should the names be updated?

cells

numeric. Cell numbers to update (1-indexed). Must be used together with values

values

numeric. New values for the specified cells. Can be a single value (recycled), one value per cell (applied to all layers), or length(cells) * length(layer) values (one per cell per layer, in layer-major order)

layer

numeric or character. Layer(s) to update. Use 0 (default) to update all layers. Positive integers or layer names select specific layers

Details

The cells and values arguments allow updating specific cell values on disk without loading the raster into memory. This is useful for modifying very large rasters that cannot fit in memory. See set.values for modifying values of in-memory rasters.

Examples

## update metadata
s <- rast(system.file("ex/logo.tif", package="terra"))   
fname <- paste0(tempfile(), ".tif")
x <- writeRaster(s*1, fname)

ext(x) <- ext(x) + 1
crs(x) <- "+proj=utm +zone=1"
names(x) <- LETTERS[1:3]

update(x, crs=TRUE, extent=TRUE, names=TRUE)

rast(fname)

## update cell values on disk
r <- rast(nrows=10, ncols=10, vals=1:100)
f <- paste0(tempfile(), ".tif")
x <- writeRaster(r, f)
x[c(1, 2, 50, 51, 100)]
update(x, cells=c(1, 50, 100), values=c(999, 888, 777))
rast(f)[c(1, 2, 50, 51, 100)]

## update specific layer only
r <- rast(nrows=5, ncols=5, nlyr=3, vals=1:75)
f <- paste0(tempfile(), ".tif")
x <- writeRaster(r, f, datatype="FLT4S")
x[c(1, 2, 25, 26)]
update(x, cells=c(1, 25), values=c(0, 0), layer=2)
rast(f)[c(1, 2, 25, 26)]