Dimensions

Dimensions are used to define the shape of data in netCDF. More...

Functions
int	nc_def_dim (int ncid, const char *name, size_t len, int *idp)
	Define a new dimension. More...
int	nc_inq_dim (int ncid, int dimid, char *name, size_t *lenp)
	Find the name and length of a dimension. More...
int	nc_inq_dimid (int ncid, const char *name, int *idp)
	Find the ID of a dimension from the name. More...
int	nc_inq_dimlen (int ncid, int dimid, size_t *lenp)
	Find the length of a dimension. More...
int	nc_inq_dimname (int ncid, int dimid, char *name)
	Find out the name of a dimension. More...
int	nc_inq_ndims (int ncid, int *ndimsp)
	Find the number of dimensions. More...
int	nc_inq_unlimdim (int ncid, int *unlimdimidp)
	Find the ID of the unlimited dimension. More...
int	nc_rename_dim (int ncid, int dimid, const char *name)
	Rename a dimension. More...

Detailed Description

Dimensions are used to define the shape of data in netCDF.

Dimensions for a netCDF dataset are defined when it is created, while the netCDF dataset is in define mode. Additional dimensions may be added later by reentering define mode. A netCDF dimension has a name and a length. In a netCDF classic or 64-bit offset file, at most one dimension can have the unlimited length, which means variables using this dimension can grow along this dimension. In a netCDF-4 file multiple unlimited dimensions are supported.

There is a suggested limit (1024) to the number of dimensions that can be defined in a single netCDF dataset. The limit is the value of the predefined macro NC_MAX_DIMS. The purpose of the limit is to make writing generic applications simpler. They need only provide an array of NC_MAX_DIMS dimensions to handle any netCDF dataset. The implementation of the netCDF library does not enforce this advisory maximum, so it is possible to use more dimensions, if necessary, but netCDF utilities that assume the advisory maximums may not be able to handle the resulting netCDF datasets.

NC_MAX_VAR_DIMS, which must not exceed NC_MAX_DIMS, is the maximum number of dimensions that can be used to specify the shape of a single variable. It is also intended to simplify writing generic applications.

Ordinarily, the name and length of a dimension are fixed when the dimension is first defined. The name may be changed later, but the length of a dimension (other than the unlimited dimension) cannot be changed without copying all the data to a new netCDF dataset with a redefined dimension length.

Dimension lengths in the C interface are type size_t rather than type int to make it possible to access all the data in a netCDF dataset on a platform that only supports a 16-bit int data type, for example MSDOS. If dimension lengths were type int instead, it would not be possible to access data from variables with a dimension length greater than a 16-bit int can accommodate.

A netCDF dimension in an open netCDF dataset is referred to by a small integer called a dimension ID. In the C interface, dimension IDs are 0, 1, 2, ..., in the order in which the dimensions were defined.

Operations supported on dimensions are:

• Create a dimension, given its name and length.
• Get a dimension ID from its name.
• Get a dimension's name and length from its ID.
• Rename a dimension.

Function Documentation

nc_def_dim()

int nc_def_dim	(	int	ncid,
		const char *	name,
		size_t	len,
		int *	idp
	)

Define a new dimension.

The function nc_def_dim() adds a new dimension to an open netCDF dataset in define mode. It returns (as an argument) a dimension ID, given the netCDF ID, the dimension name, and the dimension length. At most one unlimited length dimension, called the record dimension, may be defined for each classic or 64-bit offset netCDF dataset. NetCDF-4 datasets may have multiple unlimited dimensions.

Parameters

ncid	NetCDF or group ID, from a previous call to nc_open(), nc_create(), nc_def_grp(), or associated inquiry functions such as nc_inq_ncid().
name	Name of the dimension to be created.
len	Length of the dimension to be created. Use NC_UNLIMITED for unlimited dimensions.
idp	Pointer where dimension ID will be stored.

Returns

NC_NOERR No error.

NC_EBADID Not a valid ID.

NC_EMAXNAME Name is too long.

NC_EBADNAME Name breaks netCDF name rules.

NC_EINVAL Invalid input.

NC_ENOTINDEFINE Not in define mode.

NC_EDIMSIZE Invalid dimension size.

NC_EUNLIMIT NC_UNLIMITED size already in use

NC_EMAXDIMS NC_MAX_DIMS exceeded [not enforced after 4.5.0]

NC_ENAMEINUSE String match to name in use

NC_ENOMEM Memory allocation (malloc) failure

NC_EPERM Write to read only

Example

Here is an example using nc_def_dim() to create a dimension named lat of length 18 and a unlimited dimension named rec in a new netCDF dataset named foo.nc:

#include <netcdf.h>
...
int status, ncid, latid, recid;
...
status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
if (status != NC_NOERR) handle_error(status);
...
status = nc_def_dim(ncid, "lat", 18L, &latid);
if (status != NC_NOERR) handle_error(status);
status = nc_def_dim(ncid, "rec", NC_UNLIMITED, &recid);
if (status != NC_NOERR) handle_error(status);

Author

Glenn Davis, Russ Rew, Ed Hartnett, Dennis Heimbigner, Ward Fisher

Definition at line 121 of file ddim.c.

nc_inq_dim()

int nc_inq_dim	(	int	ncid,
		int	dimid,
		char *	name,
		size_t *	lenp
	)

Find the name and length of a dimension.

The length for the unlimited dimension, if any, is the number of records written so far.

Parameters

ncid	NetCDF or group ID, from a previous call to nc_open(), nc_create(), nc_def_grp(), or associated inquiry functions such as nc_inq_ncid().
dimid	Dimension ID, from a previous call to nc_inq_dimid() or nc_def_dim().
name	Returned dimension name. The caller must allocate space for the returned name. The maximum possible length, in characters, of a dimension name is given by the predefined constant NC_MAX_NAME. (This doesn't include the null terminator, so declare your array to be size NC_MAX_NAME+1). The returned character array will be null-terminated.
lenp	Pointer to location for returned length of dimension. For the unlimited dimension, this is the number of records written so far.

Returns

NC_NOERR No error.

NC_EBADID Not a valid ID.

NC_EBADDIM Invalid dimension ID or name.

Example

Here is an example using nc_inq_dim() to determine the length of a dimension named lat, and the name and current maximum length of the unlimited dimension for an existing netCDF dataset named foo.nc:

#include <netcdf.h>
...
int status, ncid, latid, recid;
size_t latlength, recs;
char recname[NC_MAX_NAME+1];
...
status = nc_open("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
status = nc_inq_unlimdim(ncid, &recid);
if (status != NC_NOERR) handle_error(status);
...
status = nc_inq_dimid(ncid, "lat", &latid);
if (status != NC_NOERR) handle_error(status);
status = nc_inq_dimlen(ncid, latid, &latlength);
if (status != NC_NOERR) handle_error(status);
 
status = nc_inq_dim(ncid, recid, recname, &recs);
if (status != NC_NOERR) handle_error(status);

Author

Glenn Davis, Russ Rew, Ed Hartnett, Dennis Heimbigner, Ward Fisher

Definition at line 216 of file ddim.c.

nc_inq_dimid()

int nc_inq_dimid	(	int	ncid,
		const char *	name,
		int *	idp
	)

Find the ID of a dimension from the name.

The function nc_inq_dimid returns (as an argument) the ID of a netCDF dimension, given the name of the dimension. If ndims is the number of dimensions defined for a netCDF dataset, each dimension has an ID between 0 and ndims-1.

Parameters

ncid	NetCDF or group ID, from a previous call to nc_open(), nc_create(), nc_def_grp(), or associated inquiry functions such as nc_inq_ncid().
name	Name of the dimension.
idp	Pointer where dimension ID will be stored.

Returns

NC_NOERR No error.

NC_EBADID Not a valid ID.

NC_EBADDIM Invalid dimension ID.

Author

Glenn Davis, Russ Rew, Ed Hartnett, Dennis Heimbigner, Ward Fisher

Definition at line 152 of file ddim.c.

nc_inq_dimlen()

int nc_inq_dimlen	(	int	ncid,
		int	dimid,
		size_t *	lenp
	)

Find the length of a dimension.

The length for the unlimited dimension, if any, is the number of records written so far.

Parameters

ncid	NetCDF or group ID, from a previous call to nc_open(), nc_create(), nc_def_grp(), or associated inquiry functions such as nc_inq_ncid().
dimid	Dimension ID, from a previous call to nc_inq_dimid() or nc_def_dim().
lenp	Pointer where the length will be stored.

Returns

NC_NOERR No error.

NC_EBADID Not a valid ID.

NC_EBADDIM Invalid dimension ID or name.

Example

Here is an example using nc_inq_dim() to determine the length of a dimension named lat, and the name and current maximum length of the unlimited dimension for an existing netCDF dataset named foo.nc:

#include <netcdf.h>
...
int status, ncid, latid, recid;
size_t latlength, recs;
char recname[NC_MAX_NAME+1];
...
status = nc_open("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
status = nc_inq_unlimdim(ncid, &recid);
if (status != NC_NOERR) handle_error(status);
...
status = nc_inq_dimid(ncid, "lat", &latid);
if (status != NC_NOERR) handle_error(status);
status = nc_inq_dimlen(ncid, latid, &latlength);
if (status != NC_NOERR) handle_error(status);
 
status = nc_inq_dim(ncid, recid, recname, &recs);
if (status != NC_NOERR) handle_error(status);

Author

Glenn Davis, Russ Rew, Ed Hartnett, Dennis Heimbigner, Ward Fisher

Definition at line 467 of file ddim.c.

nc_inq_dimname()

int nc_inq_dimname	(	int	ncid,
		int	dimid,
		char *	name
	)

Find out the name of a dimension.

Parameters

ncid	NetCDF or group ID, from a previous call to nc_open(), nc_create(), nc_def_grp(), or associated inquiry functions such as nc_inq_ncid().
dimid	Dimension ID, from a previous call to nc_inq_dimid() or nc_def_dim().
name	Returned dimension name. The caller must allocate space for the returned name. The maximum possible length, in characters, of a dimension name is given by the predefined constant NC_MAX_NAME. (This doesn't include the null terminator, so declare your array to be size NC_MAX_NAME+1). The returned character array will be null-terminated. Ignored if NULL.

Returns

NC_NOERR No error.

NC_EBADID Not a valid ID.

NC_EBADDIM Invalid dimension ID or name.

Example

Here is an example using nc_inq_dim() to determine the length of a dimension named lat, and the name and current maximum length of the unlimited dimension for an existing netCDF dataset named foo.nc:

#include <netcdf.h>
...
int status, ncid, latid, recid;
size_t latlength, recs;
char recname[NC_MAX_NAME+1];
...
status = nc_open("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
status = nc_inq_unlimdim(ncid, &recid);
if (status != NC_NOERR) handle_error(status);
...
status = nc_inq_dimid(ncid, "lat", &latid);
if (status != NC_NOERR) handle_error(status);
status = nc_inq_dimlen(ncid, latid, &latlength);
if (status != NC_NOERR) handle_error(status);
 
status = nc_inq_dim(ncid, recid, recname, &recs);
if (status != NC_NOERR) handle_error(status);

Author

Glenn Davis, Russ Rew, Ed Hartnett, Dennis Heimbigner, Ward Fisher

Definition at line 409 of file ddim.c.

nc_inq_ndims()

int nc_inq_ndims	(	int	ncid,
		int *	ndimsp
	)

Find the number of dimensions.

In a classic model netCDF file, this function returns the number of defined dimensions. In a netCDF-4/HDF5 file, this function returns the number of dimensions available in the group specified by ncid, which may be less than the total number of dimensions in a file. In a netCDF-4/HDF5 file, dimensions are in all sub-groups, sub-sub-groups, etc.

Parameters

ncid	NetCDF or group ID, from a previous call to nc_open(), nc_create(), nc_def_grp(), or associated inquiry functions such as nc_inq_ncid().
ndimsp	Pointer where number of dimensions will be written. Ignored if NULL.

Returns

NC_NOERR No error.

NC_EBADID Not a valid ID.

Author

Glenn Davis, Russ Rew, Ed Hartnett, Dennis Heimbigner, Ward Fisher

Definition at line 317 of file ddim.c.

nc_inq_unlimdim()

int nc_inq_unlimdim	(	int	ncid,
		int *	unlimdimidp
	)

Find the ID of the unlimited dimension.

This function finds the ID of the unlimited dimension. For netCDF-4/HDF5 files (which may have more than one unlimited dimension), the ID of the first unlimited dimesnion is returned. For these files, nc_inq_unlimdims() will return all the unlimited dimension IDs.

Parameters

ncid	NetCDF or group ID, from a previous call to nc_open(), nc_create(), nc_def_grp(), or associated inquiry functions such as nc_inq_ncid().
unlimdimidp	Pointer where unlimited dimension ID will be stored. If there is no unlimited dimension, -1 will be stored here. Ignored if NULL.

Returns

NC_NOERR No error.

NC_EBADID Not a valid ID.

Author

Glenn Davis, Russ Rew, Ed Hartnett, Dennis Heimbigner, Ward Fisher

Definition at line 350 of file ddim.c.

nc_rename_dim()

int nc_rename_dim	(	int	ncid,
		int	dimid,
		const char *	name
	)

Rename a dimension.

This function renames an existing dimension in a netCDF dataset open for writing. You cannot rename a dimension to have the same name as another dimension.

For netCDF classic and 64-bit offset files, if the new name is longer than the old name, which has been flushed to disk, the netCDF dataset must be in define mode.

For netCDF-4 files the length of the name is not checked against the length of the old name, even for classic model files. This is due to the difficulty of exactly reproducing classic library behavior in this case.

Parameters

ncid	NetCDF or group ID, from a previous call to nc_open(), nc_create(), nc_def_grp(), or associated inquiry functions such as nc_inq_ncid().
dimid	Dimension ID, from a previous call to nc_inq_dimid() or nc_def_dim().
name	New name for dimension. Must be a null-terminated string with length less than NC_MAX_NAME.

Returns

NC_NOERR No error.

NC_EBADID Not a valid ID.

NC_EBADDIM Invalid dimension ID or name.

NC_ENAMEINUSE String match to name in use

NC_ENOMEM Memory allocation (malloc) failure

NC_EPERM Write to read only

NC_ENOTINDEFINE Not in define mode and new name is longer than old.

Example

Here is an example using nc_rename_dim to rename the dimension lat to latitude in an existing netCDF dataset named foo.nc:

#include <netcdf.h>
...
int status, ncid, latid;
...
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
...
status = nc_redef(ncid);
if (status != NC_NOERR) handle_error(status);
status = nc_inq_dimid(ncid, "lat", &latid);
if (status != NC_NOERR) handle_error(status);
status = nc_rename_dim(ncid, latid, "latitude");
if (status != NC_NOERR) handle_error(status);
status = nc_enddef(ncid);
if (status != NC_NOERR) handle_error(status);

Author

Glenn Davis, Russ Rew, Ed Hartnett, Dennis Heimbigner, Ward Fisher

Definition at line 285 of file ddim.c.