NEP Format Readers

NEP implements five NetCDF User Defined Format (UDF) handlers that allow external scientific data formats to be opened with the standard nc_open() API. All readers are disabled by default and must be enabled at build time.

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

All five readers can be enabled simultaneously — there are no mutual-exclusivity restrictions as of v2.2.0.

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

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

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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 */

Install path:

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