.. _iris.experimental.ugrid.cf:

==========================
iris.experimental.ugrid.cf
==========================



.. currentmodule:: iris

.. automodule:: iris.experimental.ugrid.cf

In this module:

 * :py:obj:`CFUGridAuxiliaryCoordinateVariable`
 * :py:obj:`CFUGridConnectivityVariable`
 * :py:obj:`CFUGridGroup`
 * :py:obj:`CFUGridMeshVariable`
 * :py:obj:`CFUGridReader`


A CF-UGRID auxiliary coordinate variable is a CF-netCDF auxiliary
coordinate variable representing the element (node/edge/face/volume)
locations (latitude, longitude or other spatial coordinates, and optional
elevation or other coordinates). These auxiliary coordinate variables will
have length n-elements.

For elements other than nodes, these auxiliary coordinate variables may
have in turn a ``bounds`` attribute that specifies the bounding coordinates
of the element (thereby duplicating the data in the ``node_coordinates``
variables).

Identified by the CF-netCDF variable attribute
``node_``/``edge_``/``face_``/``volume_coordinates``.

.. seealso::

    The UGRID Conventions, https://ugrid-conventions.github.io/ugrid-conventions/

..

    .. autoclass:: iris.experimental.ugrid.cf.CFUGridAuxiliaryCoordinateVariable
        :members:
        :undoc-members:
        :inherited-members:


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A CF_UGRID connectivity variable points to an index variable identifying
for every element (edge/face/volume) the indices of its corner nodes. The
connectivity array will thus be a matrix of size n-elements x n-corners.
For the indexing one may use either 0- or 1-based indexing; the convention
used should be specified using a ``start_index`` attribute to the index
variable.

For face elements: the corner nodes should be specified in anticlockwise
direction as viewed from above. For volume elements: use the
additional attribute ``volume_shape_type`` which points to a flag variable
that specifies for every volume its shape.

Identified by a CF-netCDF variable attribute equal to any one of the values
in :attr:`~iris.experimental.ugrid.mesh.Connectivity.UGRID_CF_ROLES`.

.. seealso::

    The UGRID Conventions, https://ugrid-conventions.github.io/ugrid-conventions/

..

    .. autoclass:: iris.experimental.ugrid.cf.CFUGridConnectivityVariable
        :members:
        :undoc-members:
        :inherited-members:


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Represents a collection of 'NetCDF Climate and Forecast (CF) Metadata
Conventions' variables and netCDF global attributes.

Specialisation of :class:`~iris.fileformats.cf.CFGroup` that includes extra
collections for CF-UGRID-specific variable types.

..

    .. autoclass:: iris.experimental.ugrid.cf.CFUGridGroup
        :members:
        :undoc-members:
        :inherited-members:


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A CF-UGRID mesh variable is a dummy variable for storing topology
information as attributes. The mesh variable has the ``cf_role``
'mesh_topology'.

The UGRID conventions describe define the mesh topology as the
interconnection of various geometrical elements of the mesh. The pure
interconnectivity is independent of georeferencing the individual
geometrical elements, but for the practical applications for which the
UGRID CF extension is defined, coordinate data will always be added.

Identified by the CF-netCDF variable attribute 'mesh'.

.. seealso::

    The UGRID Conventions, https://ugrid-conventions.github.io/ugrid-conventions/

..

    .. autoclass:: iris.experimental.ugrid.cf.CFUGridMeshVariable
        :members:
        :undoc-members:
        :inherited-members:


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This class allows the contents of a netCDF file to be interpreted according
to the 'NetCDF Climate and Forecast (CF) Metadata Conventions'.

Specialisation of :class:`~iris.fileformats.cf.CFReader` that can also
handle CF-UGRID-specific variable types.

..

    .. autoclass:: iris.experimental.ugrid.cf.CFUGridReader
        :members:
        :undoc-members:
        :inherited-members: