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Write a SpatRaster to a NetCDF File with Multiple Variables

Source: R/spat_write_nc.R
write_nc.Rd

This function takes a terra::SpatRaster object and writes it to a NetCDF file. Each layer of the input raster is saved as a separate, correctly named variable in the output file. This function uses the ncdf4 package for robust, low-level control over the NetCDF creation process, ensuring that layer names, CRS, and other metadata are preserved and compression is applied correctly.

Usage

write_nc(
  input_raster = NULL,
  filename = NULL,
  overwrite = FALSE,
  compression_level = 9L,
  missval = -9999L,
  var_units = ""
)

Arguments

input_raster

A terra::SpatRaster object with one or more layers. The names of the layers will be used as the variable names in the NetCDF file.

filename

Character. The file path for the output NetCDF file. It is recommended to use a .nc extension.

overwrite

Logical. If TRUE, an existing file at the specified filename will be overwritten. Defaults to FALSE.

compression_level

An integer between 0 (no compression) and 9 (maximum DEFLATE compression). Defaults to 9.

missval

Numeric. Value for missing values in the NetCDF file. Defaults to -9999.

var_units

A character string or a vector of character strings specifying the units for each variable. If a single string is provided, it will be applied to all variables. If a vector, its length must match the number of layers in input_raster. Defaults to empty string "".

Value

This function does not return a value. It is called for its side effect of writing a file to disk.

Author

Ahmed El-Gabbas

Examples


require(terra)
require(ncdf4)
#> Loading required package: ncdf4
require(dismo)

fnames <- list.files(
  path = paste(system.file(package = "dismo"), "/ex", sep = ""),
  pattern = "grd", full.names = TRUE)

predictors <- terra::toMemory(terra::rast(fnames))
names(predictors)
#> [1] "bio1"  "bio12" "bio16" "bio17" "bio5"  "bio6"  "bio7"  "bio8"  "biome"

# Define an output file path
output_file <- tempfile(fileext = ".nc")

# Use the function to write the SpatRaster to a NetCDF file
write_nc(
  input_raster = predictors,
  filename = output_file,
  overwrite = TRUE,
  compression_level = 7)

# Verify the result
predictors2 <- terra::rast(output_file)
print(identical(names(predictors), names(predictors2)))
#> [1] TRUE

difference_raster <- predictors - predictors2
print(terra::minmax(difference_raster))
#>     bio1 bio12 bio16 bio17 bio5 bio6 bio7 bio8 biome
#> min    0     0     0     0    0    0    0    0     0
#> max    0     0     0     0    0    0    0    0     0

# Clean up the temporary file
unlink(output_file)