Grid

class ESMF.api.grid.Grid(max_index=None, num_peri_dims=0, periodic_dim=None, pole_dim=None, coord_sys=None, coord_typekind=None, staggerloc=None, pole_kind=None, filename=None, filetype=None, reg_decomp=None, decompflag=None, is_sphere=None, add_corner_stagger=None, add_user_area=None, add_mask=None, varname=None, coord_names=None, tilesize=None, regDecompPTile=None, name=None)

The Grid class is a Python wrapper object for the ESMF Grid. The individual values of all coordinate and mask arrays are referenced to those of the underlying Fortran ESMF object.

The Grid class is used to describe the geometry and discretization of logically rectangular physical grids. It also contains the description of the underlying topology and decomposition of the physical grid across the available computational resources. The most frequent use of the Grid class is to describe physical grids in user code so that sufficient information is available to perform regridding operations.

Refer to the Grid Class of the ESMF Reference Manual for more information.

A Grid can be created in two different ways, as a Grid in memory, or from SCRIP formatted or CF compliant GRIDSPEC file. The arguments for each type of Grid creation are outlined below.

Created in-memory:

REQUIRED:

Parameters

max_index (list) – An integer list of length 2 or 3, with the number of grid cells in each dimension.

OPTIONAL:

Parameters

• num_peri_dims (int) – The number of periodic dimensions, either 0 or 1. If None, defaults to 0.

• periodic_dim (int) – The periodic dimension: 0, 1 or 2. If None, defaults to 0.

• pole_dim (int) – The pole dimension 0 or 1. If None, defaults to 1.

• coord_sys (CoordSys) – Coordinate system for the Grid. If None, defaults to SPH_DEG.

• coord_typekind (TypeKind) – Type of the Grid coordinates. If None, defaults to R8.

Created either from file or in-memory:

Parameters

• staggerloc (StaggerLoc) – The stagger location of the coordinate values. If None, defaults to CENTER in 2D and CENTER_VCENTER in 3D.

• pole_kind (PoleKind) – Two item list which specifies the type of connection which occurs at the pole. The first value specifies the connection that occurs at the minimum end of the pole dimension. The second value specifies the connection that occurs at the maximum end of the pole dimension. If None, defaults to MONOPOLE.

Created from file:

REQUIRED:

Parameters

• filename (str) – The name of the NetCDF grid file.

• filetype (FileFormat) – The grid FileFormat.

OPTIONAL:

Parameters

• is_sphere (bool) – Set to True for a spherical grid, or False for regional. Defaults to True.

• add_corner_stagger (bool) – Set to True to use the information in the grid file to add the corner stagger to the grid. The coordinates for the corner stagger are required for conservative regridding. If not specified, defaults to False.

• add_user_area (bool) – Set to True to read in the cell area from the grid file; otherwise, ESMF will calculate it. Defaults to False.

• add_mask (bool) – Set to True to generate the mask using the missing_value attribute defined in varname. This argument is only supported with filetype GRIDSPEC. Defaults to False.

• varname (str) – If add_mask is True, provide a variable name stored in the grid file and the mask will be generated using the missing value of the data value of this variable. The first two dimensions of the variable has to be the longitude and the latitude dimension and the mask is derived from the first 2D values of this variable even if this data is a 3D, or 4D array. This argument is only supported with filetype GRIDSPEC. Defaults to None.

• coord_names (list) – A two-element array containing the longitude and latitude variable names in a GRIDSPEC file if there are multiple coordinates defined in the file. This argument is only supported with filetype GRIDSPEC. Defaults to None.

Cubed sphere:

REQUIRED:

Parameters

tilesize (int) – The number of elements on each side of the tile of the cubed sphere grid.

OPTIONAL:

Parameters

• regDecompPTile (list) – List of DE counts for each dimension. The second index steps through the tiles. The total deCount is determined as the sum over the products of regDecompPTile elements for each tile. By default every tile is decomposed in the same way. If the total PET count is less than 6, one tile will be assigned to one DE and the DEs will be assigned to PETs sequentially, therefore, some PETs may have more than one DE. If the total PET count is greater than 6, the total number of DEs will be a multiple of 6 and less than or equal to the total PET count. For instance, if the total PET count is 16, the total DE count will be 12 with each tile decomposed into 1x2 blocks. The 12 DEs are mapped to the first 12 PETs and the remaining 4 PETs have no DEs locally.

• name (str) – The name of the Grid.

property area

Return type

A list of numpy arrays with an entry for every stagger location of the Grid.

Returns

The Grid cell areas represented as numpy arrays of floats of size given by upper_bounds - lower_bounds.

property areatype

Return type

TypeKind

Returns

The ESMF typekind of the Grid cell areas.

property coords

Return type

2D list of numpy arrays of size given by upper_bounds - lower_bounds, where the first index represents the stagger locations of the Grid and the second index represent the coordinate dimensions of the Grid.

Returns

The coordinates of the Grid.

property coord_sys

Return type

CoordSys

Returns

The coordinate system of the Grid.

property has_corners

Return type

bool

Returns

A boolean value to tell if the Grid has corners allocated.

property lower_bounds

Return type

A list of numpy arrays with an entry for every stagger location of the Grid.

Returns

The lower bounds of the Grid represented as numpy arrays of ints of size given by upper_bounds - lower_bounds.

property mask

Return type

A list of numpy arrays with an entry for every stagger location of the Grid.

Returns

The mask of the Grid represented as numpy arrays of ints of size given by ` upper_bounds - lower_bounds`.

property max_index

Return type

A numpy array with as many values as the Grid rank.

Returns

The number of Grid cells in each dimension of the grid.

property num_peri_dims

Return type

int

Returns

The total number of periodic dimensions in the Grid.

property periodic_dim

Return type

int

Returns

The periodic dimension of the Grid (e.g. 0 for x or longitude, 1 for y or latitude, etc.).

property pole_dim

Return type

int

Returns

The pole dimension of the Grid (e.g. 0 for x or longitude, 1 for y or latitude, etc.).

property rank

Return type

int

Returns

The rank of the Grid.

property size

Return type

A list of numpy arrays with an entry for every stagger location of the Grid.

Returns

The size of the Grid represented as numpy arrays of ints of size given by upper_bounds - lower_bounds.

property staggerloc

Return type

list of bools

Returns

The stagger locations that have been allocated for the Grid.

property type

Return type

TypeKind

Returns

The ESMF typekind of the Grid coordinates.

property upper_bounds

Return type

A list of numpy arrays with an entry for every stagger location of the Grid.

Returns

The upper bounds of the Grid represented as numpy arrays of ints of size given by upper_bounds - lower_bounds.

add_coords(staggerloc=None, coord_dim=None, from_file=False)

Add coordinates to the Grid at the specified stagger location.

Parameters

• staggerloc (StaggerLoc) – The stagger location of the coordinate values. If None, defaults to CENTER in 2D and CENTER_VCENTER in 3D.

• coord_dim (int) – The dimension number of the coordinates to return e.g. [x, y, z] = (0, 1, 2), or [lon, lat] = (0, 1) (coordinates will not be returned if coord_dim is not specified and staggerlocs is a list with more than one element).

• from_file (bool) – Boolean for internal use to determine whether the Grid has already been created from file.

Returns

A numpy array of coordinate values if staggerloc and coord_dim are specified, otherwise return None.

add_item(item, staggerloc=None, from_file=False)

Allocate space for a Grid item (mask or areas) at a specified stagger location.

REQUIRED:

Parameters

item (GridItem) – The GridItem to allocate.

OPTIONAL:

Parameters

• staggerloc (StaggerLoc) – The stagger location of the item values. If None, defaults to CENTER in 2D and CENTER_VCENTER in 3D.

• from_file (bool) – Boolean for internal use to determine whether the Grid has already been created from file.

Returns

A numpy array of the mask or area values if a single staggerloc is given, otherwise return None.

copy()

Copy a Grid in an ESMF-safe manner.

Returns

A Grid shallow copy.

destroy()

Release the memory associated with a Grid.

get_coords(coord_dim, staggerloc=None)

Return a numpy array of coordinates at a specified stagger location. The returned array is NOT a copy, it is directly aliased to the underlying memory allocated by ESMF.

REQUIRED:

Parameters

coord_dim (int) – The dimension number of the coordinates to return e.g. [x, y, z] = (0, 1, 2), or [lon, lat] = (0, 1) (coordinates will not be returned if coord_dim is not specified and staggerlocs is a list with more than one element).

OPTIONAL:

Parameters

staggerloc (StaggerLoc) – The stagger location of the coordinate values. If None, defaults to CENTER in 2D and CENTER_VCENTER in 3D.

Returns

A numpy array of coordinate values at the specified staggerloc.

get_item(item, staggerloc=None)

Return a numpy array of item values at a specified stagger location. The returned array is NOT a copy, it is directly aliased to the underlying memory allocated by ESMF.

REQUIRED:

Parameters

item (GridItem) – The GridItem to return.

OPTIONAL:

Parameters

staggerloc (StaggerLoc) – The stagger location of the item values. If None, defaults to CENTER in 2D and CENTER_VCENTER in 3D.

Returns

A numpy array of mask or area values at the specified staggerloc.