write_ncdf

Export a data cube as netCDF file(s)

Description

This function will read chunks of a data cube and write them to a single (the default) or multitple (if chunked = TRUE) netCDF file(s). The resulting file(s) uses the enhanced netCDF-4 format, supporting chunking and compression.

Usage

write_ncdf(
  x,
  fname = tempfile(pattern = "gdalcubes", fileext = ".nc"),
  overwrite = FALSE,
  write_json_descr = FALSE,
  with_VRT = FALSE,
  pack = NULL,
  chunked = FALSE
)

Arguments

Argument	Description
x	a data cube proxy object (class cube)
fname	output file name
overwrite	logical; overwrite output file if it already exists
write_json_descr	logical; write a JSON description of x as additional file
with_VRT	logical; write additional VRT datasets (one per time slice)
pack	reduce output file size by packing values (see Details), defaults to no packing
chunked	logical; if TRUE, write one netCDF file per chunk; defaults to FALSE

Details

The resulting netCDF file(s) contain three dimensions (t, y, x) and bands as variables.

If write_json_descr is TRUE, the function will write an addition file with the same name as the NetCDF file but “.json” suffix. This file includes a serialized description of the input data cube, including all chained data cube operations.

To reduce the size of created files, values can be packed by applying a scale factor and an offset value and using a smaller integer data type for storage (only supported if chunked = TRUE). The pack argument can be either NULL (the default), or a list with elements type, scale, offset, and nodata. type can be any of “uint8”, “uint16” , “uint32”, “int16”, or “int32”. scale, offset, and nodata must be numeric vectors with length one or length equal to the number of data cube bands (to use different values for different bands). The helper function pack_minmax can be used to derive offset and scale values with maximum precision from minimum and maximum data values on original scale.

If chunked = TRUE, names of the produced files will start with name (with removed extension), followed by an underscore and the internal integer chunk number.

Value

returns (invisibly) the path of the created netCDF file(s)

Note

Packing is currently ignored if chunked = TRUE

Examples

# create image collection from example Landsat data only 
# if not already done in other examples
if (!file.exists(file.path(tempdir(), "L8.db"))) {
  L8_files <- list.files(system.file("L8NY18", package = "gdalcubes"),
                         ".TIF", recursive = TRUE, full.names = TRUE)
  create_image_collection(L8_files, "L8_L1TP", file.path(tempdir(), "L8.db"), quiet = TRUE) 
}

L8.col = image_collection(file.path(tempdir(), "L8.db"))
v = cube_view(extent=list(left=388941.2, right=766552.4, 
              bottom=4345299, top=4744931, t0="2018-04", t1="2018-04"),
              srs="EPSG:32618", nx = 497, ny=526, dt="P1M")
write_ncdf(select_bands(raster_cube(L8.col, v), c("B04", "B05")), fname=tempfile(fileext = ".nc"))

See Also

gdalcubes_options

pack_minmax