2. Resources

What are the different formats implemented in my configuration ? (some may be deactivated in config for simpler installation)

>>> import epygram
>>> epygram.init_env()
>>> epygram.config.implemented_formats
['netCDF', 'GRIB', 'GeoPoints', 'TIFFMF', 'FA', 'LFI', 'DDHLFA', 'LFA']

There is a proxy to open an existing resource without making an explicit reference to its format, e.g.:

>>> a_resource = epygram.formats.resource('ICMSHAROM+0042', 'r')

(where ‘r’ stands for ‘read’ opening mode and ‘ICMSHAROM+0042’ is the filename of the resource), that uses the underneath guessing function, that you may find useful (?)

>>> epygram.formats.guess('ICMSHAROM+0042')

For opening a new resource in writing mode, specifying the format is though necessary:

>>> a_resource = epygram.formats.resource('ICMSHAROM+0042_new', 'w', fmt='FA')

All resources of different formats share a set of common methods, such as listfields(), readfield() and writefield(), that behave similarly: readfield() always return the same kind of objects: Fields.

2.1. Explore resources

Let’s open an historic FA file from AROME and explore it.

>>> r = epygram.formats.resource('ICMSHAROM+0042', 'r')
>>> r.format
>>> type(r)
<class 'epygram.formats.FA.FA'>
>>> r.isopen
>>> r.openmode

But I may want later to add a field in this resource ? Let’s reopen it with ‘append’ mode.

>>> r.close()
>>> r.isopen
>>> r.open(openmode='a')
>>> r.openmode

Where is my resource stored ?

>>> r.container.absdir
>>> r.container.basename
>>> print r.container.abspath

Now let’s explore what’s inside this FA file.

>>> r.empty
# there are fields in there
>>> r.listfields()
>>> len(r.listfields())

2.1.1. Some FA additional properties

The case of FA is a bit specific in that the temporal and geometric metadata is common to the whole resource and shared by all fields. Therefore, the resource “has a geometry”:

>>> print r.geometry
D3ProjectedGeometry containing:
    _center_lon: Angle containing:
        _degrees: 2.0
        _radians: 0.0349065850399
        _origin_value: 0.0349065850399
        _origin_unit: radians
        reference_lat: Angle containing:
            _cos_sin: (0.6858183529273761, 0.7277727576572106)
            _degrees: 46.7
            _radians: 0.815068760681
            _origin_value: 0.815068760681
            _origin_unit: radians
        reference_lon: Angle containing:

and optionally a spectral geometry as well:

>>> print r.spectral_geometry
SpectralGeometry containing:
        in_X: 719
        in_Y: 767
        shape: elliptic
    space: bi-fourier

and also a validity (embedded in a list of 1 element, because time can be a dimension of fields):

>>> print r.validity[0]
FieldValidity containing:
    _basis: 2014-12-01 00:00:00
    _date_time: 2014-12-02 18:00:00
    _statistical_process_on_duration: None
    _cumulativeduration: 3:00:00

Here, we can see the validity is 2014-12-02 18:00:00, starting from basis 2014-12-01 00:00:00, which mean the term of the resource is 18h.

Also, has been included a function to look for fields with a generic seed, e.g.:

>>> r.find_fields_in_resource('*RAY*')
>>> r.find_fields_in_resource('S06[1-3]WIND.?.PHYS')
>>> r.find_fields_in_resource(['S090TEMP*', 'SURF*'])

The encoding of fields is also available:

  • on request:

    >>> r.fieldencoding('SURFTEMPERATURE')
    {'spectral': False, 'KSTRON': 0, 'KPUILA': 0, 'KNGRIB': 2, 'KNBITS': 16}
    >>> r.fieldencoding('SPECSURFGEOPOTEN')
    {'spectral': True, 'KSTRON': 0, 'KPUILA': 0, 'KNGRIB': 0, 'KNBITS': 0}
  • and stored by time of reading:

    >>> r.readfield('S001TEMPERATURE')
    >>> r.fieldscompression
    {'S001TEMPERATURE': {'KNBPDG': 18, 'KSTRON': 106, 'KPUILA': 1, 'KNGRIB': 2, 'KNBCSP': 18},

2.2. Field identifier (fid)

FA fields are identified by a character string name. Other formats may identify fields differently, for instance GRIB with a set of key:value pairs.

As an example for GRIB, the epygram.formats.GRIB.GRIB.listfields method returns a list of dicts:

>>> g = epygram.formats.resource('GRIDHSTFRANGP0025+0003', 'r')
>>> g.format
>>> g.listfields()
[{'typeOfLevel': 'surface', 'indicatorOfTypeOfLevel': 1, 'name': 'Temperature',
'level': 0, 'table2Version': 1, 'editionNumber': 1, 'shortName': 't',
'paramId': 130, 'indicatorOfParameter': 11},

Field identifiers as an attribute of epygram.fields — Fields objects will be detailed in section Field identifier of the tutorial.

2.3. Juggling with resources

Transferring a field from one resource to another is almost as simple as telling it:

>>> source_r = epygram.formats.resource('ICMSHAROM+0042', 'r')
>>> dest_r = epygram.formats.resource('ICMSHAROM+0042_bis', 'a')
>>> f = source_r.readfield('SURFTEMPERATURE')
>>> type(f)
<class 'epygram.fields.H2DField.H2DField'>
>>> dest_r.writefield(f)
# [2016/05/04-15:20:53][epygram.formats.FA][writefield:0980][INFO]: there
already is a field with the same name in this FA: overwrite.