R: Export a data cube as netCDF file(s)

write_ncdf {gdalcubes} | R Documentation

## 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

`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`

### See Also

`gdalcubes_options`

`pack_minmax`

### 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"))
    }

    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"))

[Package gdalcubes version 0.6.0 Index]