Update a raster file — update • terra

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 class 'SpatRaster'
update(object, crs=FALSE, extent=FALSE, names=FALSE,
    cells=NULL, values=NULL, layer=0)

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

Value

SpatRaster (invisibly)

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)
#> class       : SpatRaster
#> size        : 77, 101, 3  (nrow, ncol, nlyr)
#> resolution  : 1.019802, 1.025974  (x, y)
#> extent      : -1, 102, -1, 78  (xmin, xmax, ymin, ymax)
#> coord. ref. : WGS 84 / UTM zone 1N (EPSG:32601)
#> source      : file21527ac06d2a.tif
#> names       :   A,   B,   C
#> min values  :   0,   0,   0
#> max values  : 255, 255, 255

## 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)]
#>   lyr.1
#> 1     1
#> 2     2
#> 3    50
#> 4    51
#> 5   100
update(x, cells=c(1, 50, 100), values=c(999, 888, 777))
rast(f)[c(1, 2, 50, 51, 100)]
#>   lyr.1
#> 1   999
#> 2     2
#> 3   888
#> 4    51
#> 5   777

## 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)]
#>   lyr.1 lyr.2 lyr.3
#> 1     1    26    51
#> 2     2    27    52
#> 3    25    50    75
#> 4    NA    NA    NA
update(x, cells=c(1, 25), values=c(0, 0), layer=2)
rast(f)[c(1, 2, 25, 26)]
#>   lyr.1 lyr.2 lyr.3
#> 1     1     0    51
#> 2     2    27    52
#> 3    25     0    75
#> 4    NA    NA    NA