Overview

NEP (NetCDF Expansion Pack) extends NetCDF-4 with high-performance compression and multi-format data access.

Compression Filters

LZ4 and BZIP2 HDF5 filter plugins for NetCDF-4 files, both enabled by default. LZ4 targets speed (2–3× faster than DEFLATE); BZIP2 targets ratio (ideal for archival).

See Compression Filters — algorithm details, C/Fortran API reference, and performance benchmarks.

Format Readers

Five NetCDF UDF handlers that expose external scientific formats through the standard nc_open() API, all disabled by default:

GeoTIFF (UDF0/UDF1): Geospatial raster files with CF-1.8 CRS metadata
GRIB2 (UDF2): Meteorological and oceanographic NWP model output (NOAA GFS, NAM, HRRR)
FITS (UDF3): Astronomical images and tables from HST, JWST, Chandra, and other observatories
CDF (UDF4): NASA space physics and heliophysics time-series data
PDS4 (UDF5): NASA/ESA planetary science archives (Curiosity, Perseverance, Cassini, and others)

See Format Readers — usage, code examples, and dependency information for each reader.

NEXTCDF-4 Backend

Optional alternative NetCDF-4/HDF5 backend selected explicitly with NC_NEXTCDF4 (UDF9). It supports the full enhanced NetCDF-4 data model, variable I/O, chunking, compression, and new atomic types (NC_FLOAT16, small floating-point types, complex numbers, bitfields, and HDF5 references) while coexisting with netcdf-c's built-in HDF5 backend. Files written in NC_NETCDF4_MODEL compatibility mode remain readable by upstream netcdf-c.

See NEXTCDF-4 — selection flags, compatibility modes, supported types, and examples.

Example Programs

Over 55 C and Fortran programs covering classic NetCDF, NetCDF-4, NcZarr, OPeNDAP remote access, performance tuning, and parallel I/O. Companion code for The NetCDF Developer's Handbook, Second Edition.

See Example Programs — complete program listing by category.

Installation

NEP requires:

NetCDF-C library (v4.10.1+) (required for UDF slots > 2 used by FITS, CDF, and PDS4)
HDF5 library (v1.10+) and its dependencies
LZ4 library
BZIP2 library
NetCDF-Fortran library (optional, for Fortran support)
NASA CDF library v3.9+ (optional, for CDF file reading)
libgeotiff and libtiff (optional, for GeoTIFF file reading; --enable-geotiff)
NOAA NCEPLIBS-g2c >= 2.1.0 and libjasper >= 3.0.0 (optional, for GRIB2 file reading; --enable-grib2)
CFITSIO >= 3.0 (optional, for FITS file reading; --enable-fits)
libxml2 >= 2.9 (optional, for PDS4 file reading; --enable-pds4)

Build with CMake or Autotools:

# CMake
cmake -B build -DCMAKE_INSTALL_PREFIX=/usr/local
cmake --build build
cmake --install build
 
# Autotools
./configure --prefix=/usr/local
make
make install

Build Options

See the Configuration Options section of the README for the full CMake and Autotools option reference.

API Documentation

Key API reference pages:

Refer to the documentation header for the exact version of NEP corresponding to this build.

License

See the COPYRIGHT file for licensing information.