The main purpose of this method is to allow correct reading of a SpatRaster that is based on a file that has an incorrect NA flag. The file is not changed, but flagged value is set to NA when values are read from the file ("lazy evaluation"). In contrast, if the values are in memory the change is made immediately.
To change values, it is generally better to use
# S4 method for SpatRaster NAflag(x) # S4 method for SpatRaster NAflag(x)<-value
numeric. The value to be interpreted as NA; set this before reading the values from the file. This can be a single value, or multiple values, one for each data source (file / subdataset)
none or numeric
s <- rast(system.file("ex/logo.tif", package="terra"))[] NAflag(s) <- 255 plot(s) NAflag(s) #>  255