NetCDF Expansion Pack (NEP) - Public API. More...

#include <stdio.h>
#include <netcdf.h>
#include <netcdf_filter.h>

Macros
#define	NC_FLOAT16 17

#define	NC_BFLOAT16 18

#define	NC_FLOAT8_E4M3 19

#define	NC_FLOAT8_E5M2 20

#define	NC_FLOAT6_E2M3 21

#define	NC_FLOAT6_E3M2 22

#define	NC_FLOAT4_E2M1 23

#define	NC_COMPLEX 24

#define	NC_DOUBLECOMPLEX 25

#define	NC_BITFIELD8 26

#define	NC_BITFIELD16 27

#define	NC_BITFIELD32 28

#define	NC_BITFIELD64 29

#define	NC_REF_OBJECT 30

#define	NC_REF_REGION 31

#define	BZIP2_ID 307

#define	LZ4_ID 32004

#define	LZF_ID 32000

#define	NEP_UDF_GEOTIFF_BIGTIFF NC_UDF0

#define	NEP_UDF_GEOTIFF_STANDARD NC_UDF1

#define	NEP_UDF_GRIB2 NC_UDF2

#define	NEP_UDF_CDF NC_UDF4

#define	NEP_UDF_FITS NC_UDF3

#define	NEP_UDF_PDS4 NC_UDF5

#define	NEP_UDF_DICOM NC_UDF6

#define	NEP_UDF_PDB NC_UDF7

#define	NEP_UDF_MMCIF NC_UDF8

#define	NEP_UDF_NEXTCDF4 NC_UDF9

#define	NC_NEXTCDF4 NEP_UDF_NEXTCDF4

#define	NC_NETCDF4_MODEL 0x04000000

#define	NEP_MAGIC_GEOTIFF_STANDARD "II*"

#define	NEP_MAGIC_GEOTIFF_BIGTIFF "II+"

#define	NEP_MAGIC_CDF "\xCD\xF3\x00\x01"

#define	NEP_MAGIC_GRIB2 "GRIB"

#define	NEP_MAGIC_FITS "SIMPLE"

#define	NEP_MAGIC_PDS4 "<?xml"

#define	NEP_MAGIC_DICOM "DICM"

#define	NEP_MAGIC_PDB "HEADER"

#define	NEP_MAGIC_MMCIF "data_"

#define	NEP_FORMAT_NAME_GEOTIFF "GeoTIFF"

#define	NEP_FORMAT_NAME_CDF "NASA CDF"

#define	NEP_FORMAT_NAME_GRIB2 "GRIB2"

#define	NEP_FORMAT_NAME_FITS "FITS"

#define	NEP_FORMAT_NAME_PDS4 "PDS4"

#define	NEP_FORMAT_NAME_DICOM "DICOM"

#define	NEP_FORMAT_NAME_PDB "PDB"

#define	NEP_FORMAT_NAME_MMCIF "mmCIF"

Functions
int	nc_def_var_bzip2 (int ncid, int varid, int level)

int	nc_inq_var_bzip2 (int ncid, int varid, int bzip2p, int levelp)

int	nc_def_var_lz4 (int ncid, int varid, int level)

int	nc_inq_var_lz4 (int ncid, int varid, int lz4p, int levelp)

int	nc_def_var_lzf (int ncid, int varid)

int	nc_inq_var_lzf (int ncid, int varid, int *lzfp)

Detailed Description

NetCDF Expansion Pack (NEP) - Public API.

Defines compression filter IDs and API, and the centralized mapping of file formats to NetCDF User-Defined Format (UDF) slot numbers.

UDF Slot Allocation

NetCDF-C 4.10.0+ provides 10 UDF slots (UDF0-UDF9):

UDF0: GeoTIFF BigTIFF (magic: "II+")
UDF1: GeoTIFF standard TIFF (magic: "II*")
UDF2: GRIB2 meteorological data (magic: "GRIB")
UDF3: FITS astronomical data (magic: "SIMPLE")
UDF4: NASA CDF format (magic: 0xCDF30001)
UDF5: PDS4 planetary data system (magic: "<?xml")
UDF6: DICOM medical imaging data (magic: "DICM")
UDF7: Legacy PDB protein structure data (magic: "HEADER")
UDF8: PDBx/mmCIF protein structure data (magic: "data_")
UDF9: NEXTCDF-4 HDF5 backend

Author: Edward Hartnett

Date: Nov 13, 2025

Copyright: Intelligent Data Design, Inc. All rights reserved.

Macro Definition Documentation

◆ BZIP2_ID

#define BZIP2_ID 307

The filter ID for BZIP2 compression.

◆ LZ4_ID

#define LZ4_ID 32004

The filter ID for LZ4 compression.

◆ LZF_ID

#define LZF_ID 32000

The filter ID for LZF compression.

◆ NC_BFLOAT16

#define NC_BFLOAT16 18

NEXTCDF-4 16-bit bfloat16 floating point type (HDF5 2.1.1+).

◆ NC_BITFIELD16

#define NC_BITFIELD16 27

NEXTCDF-4 16-bit bitfield type.

◆ NC_BITFIELD32

#define NC_BITFIELD32 28

NEXTCDF-4 32-bit bitfield type.

◆ NC_BITFIELD64

#define NC_BITFIELD64 29

NEXTCDF-4 64-bit bitfield type.

◆ NC_BITFIELD8

#define NC_BITFIELD8 26

NEXTCDF-4 8-bit bitfield type.

◆ NC_COMPLEX

#define NC_COMPLEX 24

NEXTCDF-4 single-precision complex number type.

◆ NC_DOUBLECOMPLEX

#define NC_DOUBLECOMPLEX 25

NEXTCDF-4 double-precision complex number type.

◆ NC_FLOAT16

#define NC_FLOAT16 17

NEXTCDF-4 16-bit IEEE 754 half-precision floating point type.

◆ NC_FLOAT4_E2M1

#define NC_FLOAT4_E2M1 23

NEXTCDF-4 4-bit E2M1 floating point type (HDF5 2.1.1+).

◆ NC_FLOAT6_E2M3

#define NC_FLOAT6_E2M3 21

NEXTCDF-4 6-bit E2M3 floating point type (HDF5 2.1.1+).

◆ NC_FLOAT6_E3M2

#define NC_FLOAT6_E3M2 22

NEXTCDF-4 6-bit E3M2 floating point type (HDF5 2.1.1+).

◆ NC_FLOAT8_E4M3

#define NC_FLOAT8_E4M3 19

NEXTCDF-4 8-bit E4M3 floating point type (HDF5 2.1.1+).

◆ NC_FLOAT8_E5M2

#define NC_FLOAT8_E5M2 20

NEXTCDF-4 8-bit E5M2 floating point type (HDF5 2.1.1+).

◆ NC_REF_OBJECT

#define NC_REF_OBJECT 30

NEXTCDF-4 object reference type.

◆ NC_REF_REGION

#define NC_REF_REGION 31

NEXTCDF-4 dataset region reference type.

Function Documentation

◆ nc_def_var_bzip2()

int nc_def_var_bzip2	(	int	ncid,
		int	varid,
		int	level
	)

nep supports compression filters for netCDF/HDF5 files which are not natively supported by the netCDF C library.

BZIP2

Bzip2 is a free and open-source file compression program that uses the Burrows–Wheeler algorithm. For more information see https://www.sourceware.org/bzip2/ and https://en.wikipedia.org/wiki/Bzip2.

In C:

In Fortran:

nf90_def_var_bzip2()
nf90_inq_var_bzip2() Turn on bzip2 compression for a variable.

Parameters

ncid	File ID.
varid	Variable ID.
level	From 1 to 9. Set the block size to 100k, 200k ... 900k when compressing. (bzip2 default level is 9).

Returns: 0 for success, error code otherwise.

Author: Edward Hartnett

◆ nc_def_var_lz4()

int nc_def_var_lz4	(	int	ncid,
		int	varid,
		int	level
	)

Turn on lz4 compression for a variable.

Parameters

ncid	File ID.
varid	Variable ID.
level	From 1 to 9. Set the block size to 100k, 200k ... 900k when compressing. (lz4 default level is 9).

Returns: 0 for success, error code otherwise.

Author: Edward Hartnett

◆ nc_def_var_lzf()

int nc_def_var_lzf	(	int	ncid,
		int	varid
	)

◆ nc_inq_var_bzip2()

int nc_inq_var_bzip2	(	int	ncid,
		int	varid,
		int *	bzip2p,
		int *	levelp
	)

Learn whether bzip2 compression is on for a variable, and, if so, the level setting.

Parameters

ncid	File ID.
varid	Variable ID.
bzip2p	Pointer that gets a 0 if bzip2 is not in use for this var, and a 1 if it is. Ignored if NULL.
levelp	Pointer that gets the level setting (from 1 to 9), if bzip2 is in use. Ignored if NULL.

Returns: 0 for success, error code otherwise.

Author: Edward Hartnett

◆ nc_inq_var_lz4()

int nc_inq_var_lz4	(	int	ncid,
		int	varid,
		int *	lz4p,
		int *	levelp
	)

Learn whether lz4 compression is on for a variable, and, if so, the level setting.

Parameters

ncid	File ID.
varid	Variable ID.
lz4p	Pointer that gets a 0 if lz4 is not in use for this var, and a 1 if it is. Ignored if NULL.
levelp	Pointer that gets the acceleration setting (from 1 to 9). Ignored if NULL.

Returns: 0 for success, error code otherwise.

Author: Edward Hartnett

◆ nc_inq_var_lzf()

int nc_inq_var_lzf	(	int	ncid,
		int	varid,
		int *	lzfp
	)

Macros

Functions

Detailed Description

UDF Slot Allocation

Macro Definition Documentation

◆ BZIP2_ID

◆ LZ4_ID

◆ LZF_ID

◆ NC_BFLOAT16

◆ NC_BITFIELD16

◆ NC_BITFIELD32

◆ NC_BITFIELD64

◆ NC_BITFIELD8

◆ NC_COMPLEX

◆ NC_DOUBLECOMPLEX

◆ NC_FLOAT16

◆ NC_FLOAT4_E2M1

◆ NC_FLOAT6_E2M3

◆ NC_FLOAT6_E3M2

◆ NC_FLOAT8_E4M3

◆ NC_FLOAT8_E5M2

◆ NC_REF_OBJECT

◆ NC_REF_REGION

Function Documentation

◆ nc_def_var_bzip2()

◆ nc_def_var_lz4()

◆ nc_def_var_lzf()

◆ nc_inq_var_bzip2()

◆ nc_inq_var_lz4()

◆ nc_inq_var_lzf()