| netCDF properties | cfa_array attributes | Partitions attributes | subarray attributes |
|---|---|---|---|
| cf_role, cfa_dimensions, cfa_array | directions, pmdimensions, pmdimensions, pmshape, base, Partitions, | index, location, pdimensions, pdirections, format, punits, pcalendar, part, subarray | shape, file, dtype, ncvar, varid, file_offset, scale_factor, add_offset, lbpack, endian, _FillValue |
This standard CF property must be used to mark the netCDF variable as either an CFA variable or a CFA private variable.
It takes values of "cfa_variable" or "cfa_private" for a CFA variable or CFA private variable respectively.
| Examples | |
|---|---|
| "cfa_variable" | |
| "cfa_private" |
A netCDF property whose value is a string containing the ordered, space delimited set of the master array’s dimension names. The specified dimensions are all defined as netCDF dimensions in the CFA-netCDF file.
If missing, an empty sting or a string containing only spaces then the master array is assumed to be scalar.
| Examples | |
|---|---|
| "time lat lon" | |
| "" | |
| " " |
The master array’s dimensions are stored outside of the cfa_array property in order to provide useful information about the master array without having to decode the cfa_array string (which may not be possible in all APIs).
A netCDF property whose value is a JSON encoded associative array containing the attributes required for constructing the aggregated data array.
The dimensions, shape, dtype, units and calendar master data array parameters are specified elsewhere (by properties of the netCDF CFA variable or inferrable from the netCDF dimensions in CFA-netCDF file) and so are not required.
The encoded string may be relatively succinct, as many attributes have well defined default values.
| Examples | |
|---|---|
| "{'directions': {'lat': false, 'lon': true }, 'Partitions':[{'index': [0], 'data': {'file': 'test1.nc', 'shape': [64, 128], 'ncvar': 'tas', 'varid': 3}, 'location': [[0, 64], [0, 128]], 'format': 'netCDF'}]}" |
The JSON decoded attributes are described here:
An associative array mapping each dimension of the master array to a direction. Each direction is described as true (increasing) or false (decreasing).
If the master array is a scalar then a boolean rather than an associative array is given.
| Examples | |
|---|---|
| {'time', true, 'lat': false, 'lon', true} | |
| true | |
| false |
Note
A scalar master array may have an implied direction, e.g. if there are bounds associated with it or if it contains a pressure datum.
pmdimensions
An ordered list of the dimensions along which the master array is partitioned. Each of these dimensions is one those specified by the cfa_dimensions property (and is therefore defined as a netCDF dimension in the CFA-netCDF file).
A shape of [] means that the partition matrix is a scalar, i.e. the master array comprises a single partition.
If missing then it is assumed that the master array comprises a single partition.
Examples ['lat', 'time'] ['height'] []
An ordered list containing the number of partitions along each partitioned dimension of the master array. The sizes correspond to the pmdimensions list. This is the shape of the partition matrix.
A shape of [] means that the partition matrix is a scalar, i.e. the master array comprises a single partition.
If missing then it is assumed that the master array comprises a single partition.
| Examples | |
|---|---|
| [2, 3] | |
| [87] | |
| [] |
A string giving the base for relative file names given by file. May be an absolute or relative URL or location on the local system. If it is a relative location then it assumed to be relative to the local directory or URL base containing the CFA-netCDF file.
If set then all file names are assumed to have relative paths. If it is an empty string ('') then the base is taken as the local directory or URL base containing the CFA-netCDF file.
If missing then it is assumed that all file names are absolute paths (local files or URLs).
| Examples | |
|---|---|
| '/data/archive' | |
| '../archive/' | |
| 'http://archive/files' | |
| '' |
A list whose elements define each of the master array’s partitions. The order of the list is arbitrary since each element contains its (possibly multidimensional) index in the partition matrix.
| Examples | |
|---|---|
| [{'index': [0], 'subarray': {'shape': [2, 3], 'varid': 0, 'ncvar': 'cfa_1bE8EBC2c3'}, 'location': [[0, 1], [0, 2]]}] |
Each element of the list is an associative array which specifies a partition with the following attributes:
- index
An ordered list of indices specifying the position of the partition in the partition matrix. The indices correspond to the pmdimensions list.
An index of [] means that the partition matrix is a scalar, i.e. the master array comprises a single partition.
If missing then it is assumed that the master array comprises a single partition.
Examples [0] [2, 1] [] Note
Indices count from zero.
- location
An ordered list of ranges of indices, one for each dimension of the master data array, which describe the contiguous section of the master data array spanned by this partition. The ranges correspond to the cfa_dimensions list.
Each range is a two-element list giving a start and stop index for its dimension. For example, the range [3, 5] is equivalent to indices 3, 4 and 5; and the range [6, 6] is equivalent to index 6.
If the master data array is a scalar then it is an empty list.
Examples [[2, 2], [3, 5], [2, 56]] [[0, 0]] [] Note
Indices count from zero.
- pdimensions (optional)
An ordered list of the partition’s data array dimension names. The specified dimensions are all defined as netCDF dimensions in the CFA-netCDF file.
If there are any size 1 dimensions of the partition which are not spanned by the master array then the partition’s dimensions must be specified.
If the partition’s data array is a scalar then it may be an empty list.
If missing then it is assumed to be equal to dimensions of the master array.
Examples ['lon', 'time', lat'] [] Note
If a partition’s data array’s dimensions are not specified and the sub-array is stored in another file then it is required only that the sub-array has the same number of dimensions, with the same physical meaning and in the same order as the master array. For example, if the sub-array were in a different netCDF file, its dimensions may have different names and sizes relative to the equivalent dimensions in the CFA-netCDF file.
- pdirections (optional)
An associative array of the partition’s data array dimension directions.
Any dimension not specified is assumed to have the same direction as the corresponding master array dimension. If there are any size 1 dimensions of the partition which are not spanned by the master array then their directions must be specified. The specified dimensions are all defined as netCDF dimensions in the CFA-netCDF file.
Examples {'time', true, 'lat': true, 'lon', false} Note
A size 1 dimension may have an implied direction, e.g. if there are bounds associated with it or if it contains a pressure datum.
- punits (optional)
A string containing the units of the partition’s data array.
If missing then it is assumed to be equal to units of the master array.
Examples 'm s-1' ''
- pcalendar (optional)
A string containing the calendar of the partition’s data array.
If missing then it is assumed to be equal to calendar of the master array.
Examples 'noleap'
- part (optional)
A string defining the part of the sub-array which comprises the partition’s data array.
For each of the partition’s dimensions, the string describes the indices of the sub-array which define the partition’s data array. The indices correspond to to the pdimensions list.
Indices are contained within square or round brackets. Square brackets specify a sequence of indices along that dimension. Round brackets provide a succinct method of describing a strictly monotonic and regularly spaced sequence of indices for the dimension via start, stop and step values. For example, (0, 3, 1) is equivalent to [0, 1, 2, 3] and (10, 4, -2) is equivalent to [10, 8, 6, 4].
If missing or the string '[]' then it is assumed that the partition’s data array is the whole of the sub-array.
Examples '[(2, 5, 1), [1, 3, 4, 7], (0, 11, 2)]' '[[5, 2, 1], (5, 1, -4), (0, 0, 1)]' '[]' Note
Indices count from zero.
subarray
An associative array giving the attributes required to define the sub-array containing the partition’s data array. Only a subset of these will be required, depending on the storage format of the sub-array.
Examples {'shape': [4, 7, 3], 'ncvar': 'cfa_345eA9001D', 'varid': 10} {'file': 'temp.nc', 'ncvar': 'tas', 'shape': [1200], 'format': 'netCDF', 'varid': 1} {'dtype': 'float', 'file': 'temp.nc', 'ncvar': 'tas', 'shape': [1200], 'format': 'netCDF', 'varid': 6} {'shape': [73, 96], 'file': '../data.pp', 'file_offset': 734826, 'lbpack': 1, 'format': 'PP'} {'shape': [73, 96], 'file': 'data.pp', 'file_offset': 0, 'scale_factor': 0.01, 'format': 'PP'} The keys specify a sub-array with the following attributes:
- format (optional)
A string naming the format of the file containing the partition’s sub-array.
If missing then the format is assumed to the same as the CFA-netCDF file.
Examples 'netCDF' 'PP'
- shape
An ordered list of the sub-array’s dimension sizes. The sizes correspond to to the pdimensions list.
Examples [4, 7, 3] []
- file (optional)
A string naming the file which contains the sub-array. May be a local file or a URL.
If base has been set then the file name is assumed to be relative to it. If base is an empty string ('') then the base is taken as the local directory or URL base containing the CFA-netCDF file.
If base has not been set then the file name is assumed to be an absolute path (local file or URL).
If missing or an empty string ('') then it is assumed to be the CFA-netCDF file itself.
Examples '/home/me/file.nc' '../file2.pp' 'file3.nc' 'http://archive/data/file.nc' 'data/file.nc' ''
- dtype (optional)
The data type of the sub-array. Any of the netCDF data type strings are allowed.
If missing then the data type of the master array is assumed.
Examples 'double' 'byte' 'char'
- ncvar (optional, but required for netCDF files)
A string containing the name of the netCDF variable containing the sub-array.
Examples 'tas' The attributes ncvar and varid encode exactly the same information, but are provided to allow flexibility in the choice of library being used to interpret the CFA-netCDF file.
- varid (optional, but required for netCDF files)
The integer UNIDATA netCDF interface ID of the variable containing the sub-array.
Examples 24 0 The attributes ncvar and varid encode exactly the same information, but are provided to allow flexibility in the choice of library being used to interpret the CFA-netCDF file.
- file_offset (optional, not required for netCDF files)
The non-negative integer word address of the file where the sub-array starts. The start of the file is addressed by zero.
Examples 8460364 This is not required for a sub-array in a netCDF file, since the sub-array’s file location is given by the ncvar string.
- lbpack (optional, PP files only)
The integer PP packing code of the sub-array.
If missing then it is assumed to be 0 (unpacked).
Examples 1
- endian (optional)
A string describing the byte order of the sub-array. It takes values of 'big' (most-significant byte first) or 'little' (least-significant byte first).
If missing then it is assumed to be 'big' .
Examples 'little' 'big'
- _FillValue (optional, not required for netCDF files)
The missing data value for the sub-array.
If missing then it is assumed that there is no missing data in the sub-array.
Examples -1073741824 For netCDF files, it is assumed that the missing data value will be accounted for when reading the file.
- scale_factor (optional, non-netCDF files only)
The numeric scale factor (in the CF sense) of the sub-array.
Examples 100.0 For netCDF files, it is assumed that the scale factor will be accounted for when reading the file. Otherwise, if missing then it is assumed to be 1 (unscaled).
- add_offset (optional, non-netCDF files only)
The numeric additive offset (in the CF sense) of the sub-array.
Examples 273.15 For netCDF files, it is assumed that the additive factor will be accounted for when reading the file. Otherwise, if missing then it is assumed to be 0 (no additive offset).