NEP implements NetCDF User Defined Format (UDF) handlers that allow external scientific data formats to be opened with the standard nc_open() API, plus an optional NEXTCDF-4 backend that replaces the built-in NetCDF-4/HDF5 backend when selected explicitly. Most format readers are disabled by default and must be enabled at build time; the legacy PDB reader is enabled by default.

UDF Slot Assignments

Slot	Format	Magic / Detection	Introduced
UDF0	GeoTIFF BigTIFF	`II+`	v1.5.0
UDF1	GeoTIFF standard TIFF	`II` or `MM\x00`	v1.5.0
UDF2	GRIB2	`GRIB`	v1.7.0
UDF3	FITS	`SIMPLE`	v2.0.0
UDF4	NASA CDF	`\xCD\xF3\x00\x01`	v1.3.0
UDF5	NASA/ESA PDS4	XML root `Product_Observational`	v2.2.0
UDF6	DICOM	`DICM` at byte offset 128	v3.0.0
UDF7	Legacy PDB	`HEADER`	v3.3.0
UDF8	PDBx/mmCIF	`data_`	v3.4.0
UDF9	NEXTCDF-4	explicit `NC_NEXTCDF4`	v4.0.0

All readers can be enabled simultaneously — there are no mutual-exclusivity restrictions. The NEXTCDF-4 backend can be enabled together with all readers.

Format Reference Pages

Each NEP format reader has a dedicated page with the full mapping, build options, dependencies, resources, and examples:

Format	UDF Slot	Reference Page
GeoTIFF	UDF0 / UDF1	GeoTIFF
GRIB2	UDF2	GRIB2
FITS	UDF3	FITS
NASA CDF	UDF4	NASA CDF
NASA/ESA PDS4	UDF5	PDS4-to-NetCDF Mapping
DICOM	UDF6	DICOM
Legacy PDB	UDF7	PDB
PDBx/mmCIF	UDF8	mmCIF
NEXTCDF-4	UDF9	NEXTCDF-4

See also the native NetCDF-4 compression documentation: LZ4/BZIP2 HDF5 filters.

UDF Autoloading via `.ncrc`

NEP installs a .ncrc configuration file that enables NetCDF-C's UDF self-loading mechanism. Once configured, nc_open() and ncdump automatically select the correct format handler with no application code changes.

Setup — merge the installed file into ~/.ncrc:

cat /usr/local/share/nep/.ncrc >> ~/.ncrc

Or point NETCDF_RC to the directory for a per-session override:

export NETCDF_RC=/usr/local/share/nep

Then open any supported format transparently:

nc_open("satellite_image.tif",                  NC_NOWRITE, &ncid);  /* GeoTIFF */
nc_open("data.cdf",                             NC_NOWRITE, &ncid);  /* CDF */
nc_open("gdaswave.t00z.wcoast.0p16.f000.grib2", NC_NOWRITE, &ncid);  /* GRIB2 */
nc_open("image.fits",                           NC_NOWRITE, &ncid);  /* FITS */
nc_open("image.dcm",                            NC_UDF6,    &ncid);  /* DICOM */
nc_open("structure.pdb",                        NC_UDF7,    &ncid);  /* Legacy PDB */
nc_open("example.nc",                           NC_NEXTCDF4 | NC_NOWRITE, &ncid);  /* NEXTCDF-4 */

Install path:

Build system	Default	Override
CMake	`${prefix}/share/nep/.ncrc`	`-DNEP_NCRC_INSTALL_DIR=<path>`

Note: .ncrc autoload requires NetCDF-C built from the main branch. With NetCDF-C 4.10.0, call NC_*_initialize() explicitly before nc_open().

See the NetCDF UDF documentation for the full RC file format reference.

UDF Slot Assignments

Format Reference Pages

UDF Autoloading via .ncrc

UDF Autoloading via `.ncrc`