# Source code for iris.experimental.ugrid.utils

```
# Copyright Iris contributors
#
# This file is part of Iris and is released under the LGPL license.
# See COPYING and COPYING.LESSER in the root of the repository for full
# licensing details.
"""
Utility operations specific to unstructured data.
"""
from typing import AnyStr, Iterable, Union
import dask.array as da
import numpy as np
from iris.cube import Cube
[docs]def recombine_submeshes(
mesh_cube: Cube,
submesh_cubes: Union[Iterable[Cube], Cube],
index_coord_name: AnyStr = "i_mesh_index",
) -> Cube:
"""
Put data from sub-meshes back onto the original full mesh.
The result is a cube like ``mesh_cube``, but with its data replaced by a
combination of the data in the ``submesh_cubes``.
Parameters
----------
mesh_cube : Cube
Describes the mesh and mesh-location onto which the all the
``submesh-cubes``' data are mapped, and acts as a template for the
result.
Must have a :class:`~iris.experimental.ugrid.mesh.Mesh`.
submesh_cubes : iterable of Cube, or Cube
Cubes, each with data on a _subset_ of the ``mesh_cube`` datapoints
(within the mesh dimension).
The submesh cubes do not need to have a mesh.
There must be at least 1 of them, to determine the result phenomenon.
Their metadata (names, units and attributes) must all be the same,
_except_ that 'var_name' is ignored.
Their dtypes must all be the same.
Their shapes and dimension-coords must all match those of
``mesh_cube``, except in the mesh dimension, which can have different
sizes between the submeshes, and from the ``mesh_cube``.
The mesh dimension of each must have a 1-D coord named by
``index_coord_name``. These "index coords" can vary in length, but
they must all have matching metadata (units, attributes and names
except 'var_name'), and must also match the coord of that name in
``mesh_cube``, if there is one.
The ".points" values of the index coords specify, for each datapoint,
its location in the original mesh -- i.e. they are indices into the
relevant mesh-location dimension.
index_coord_name : Cube
Coord name of an index coord containing the mesh location indices, in
every submesh cube.
Returns
-------
result_cube
A cube with the same mesh, location, and shape as ``mesh_cube``, but
with its data replaced by that from the``submesh_cubes``.
The result phenomeon identity is also that of the``submesh_cubes``,
i.e. units, attributes and names (except 'var_name', which is None).
Notes
-----
Where regions overlap, the result data comes from the submesh cube
containing that location which appears _last_ in ``submesh_cubes``.
Where no region contains a datapoint, it will be masked in the result.
HINT: alternatively, values covered by no region can be set to the
original 'full_mesh_cube' data value, if 'full_mesh_cube' is *also* passed
as the first of the 'region_cubes'.
The ``result_cube`` dtype is that of the ``submesh_cubes``.
"""
if not submesh_cubes:
raise ValueError("'submesh_cubes' must be non-empty.")
mesh_dim = mesh_cube.mesh_dim()
if mesh_dim is None:
raise ValueError("'mesh_cube' has no \".mesh\".")
#
# Perform consistency checks on all the region-cubes.
#
if not isinstance(submesh_cubes, Iterable):
# Treat a single submesh cube input as a list-of-1.
submesh_cubes = [submesh_cubes]
result_metadata = None
result_dtype = None
indexcoord_metadata = None
for i_sub, cube in enumerate(submesh_cubes):
sub_str = (
f"Submesh cube #{i_sub + 1}/{len(submesh_cubes)}, "
f'"{cube.name()}"'
)
# Check dimensionality.
if cube.ndim != mesh_cube.ndim:
err = (
f"{sub_str} has {cube.ndim} dimensions, but "
f"'mesh_cube' has {mesh_cube.ndim}."
)
raise ValueError(err)
# Get cube metadata + dtype : must match, and will apply to the result
dtype = cube.dtype
metadata = cube.metadata._replace(var_name=None)
if i_sub == 0:
# Store the first-cube metadata + dtype as reference
result_metadata = metadata
result_dtype = dtype
else:
# Check subsequent region-cubes metadata + dtype against the first
if metadata != result_metadata:
err = (
f"{sub_str} has metadata {metadata}, "
"which does not match that of the other region_cubes, "
f"which is {result_metadata}."
)
raise ValueError(err)
elif dtype != result_dtype:
err = (
f"{sub_str} has a dtype of {dtype}, "
"which does not match that of the other region_cubes, "
f"which is {result_dtype}."
)
raise ValueError(err)
# For each dim, check that coords match other regions, and full-cube
for i_dim in range(mesh_cube.ndim):
if i_dim == mesh_dim:
# mesh dim : look for index coords (by name)
full_coord = mesh_cube.coords(
name_or_coord=index_coord_name, dimensions=(i_dim,)
)
sub_coord = cube.coords(
name_or_coord=index_coord_name, dimensions=(i_dim,)
)
else:
# non-mesh dims : look for dim-coords (only)
full_coord = mesh_cube.coords(
dim_coords=True, dimensions=(i_dim,)
)
sub_coord = cube.coords(dim_coords=True, dimensions=(i_dim,))
if full_coord:
(full_coord,) = full_coord
full_dimname = full_coord.name()
full_metadata = full_coord.metadata._replace(var_name=None)
if sub_coord:
(sub_coord,) = sub_coord
sub_dimname = sub_coord.name()
sub_metadata = sub_coord.metadata._replace(var_name=None)
err = None
# N.B. checks for mesh- and non-mesh-dims are different
if i_dim != mesh_dim:
# i_dim == mesh_dim : checks for non-mesh dims
if full_coord and not sub_coord:
err = (
f"{sub_str} has no dim-coord for dimension "
f"{i_dim}, to match the 'mesh_cube' dimension "
f'"{full_dimname}".'
)
elif sub_coord and not full_coord:
err = (
f'{sub_str} has a dim-coord "{sub_dimname}" for '
f"dimension {i_dim}, but 'mesh_cube' has none."
)
elif sub_coord != full_coord:
err = (
f'{sub_str} has a dim-coord "{sub_dimname}" for '
f"dimension {i_dim}, which does not match that "
f"of 'mesh_cube', \"{full_dimname}\"."
)
else:
# i_dim == mesh_dim : different rules for this one
if not sub_coord:
# Must have an index coord on the mesh dimension
err = (
f'{sub_str} has no "{index_coord_name}" coord on '
f"the mesh dimension (dimension {mesh_dim})."
)
elif full_coord and sub_metadata != full_metadata:
# May *not* have full-cube index, but if so it must match
err = (
f"{sub_str} has an index coord "
f'"{index_coord_name}" whose ".metadata" does not '
f"match that of the same name in 'mesh_cube' : "
f"{sub_metadata} != {full_metadata}."
)
else:
# At this point, we know we *have* an index coord, and it does
# not conflict with the one on 'mesh_cube' (if any).
# Now check for matches between the region cubes.
if indexcoord_metadata is None:
# Store first occurrence (from first region-cube)
indexcoord_metadata = sub_metadata
elif sub_metadata != indexcoord_metadata:
# Compare subsequent occurrences (from other region-cubes)
err = (
f"{sub_str} has an index coord "
f'"{index_coord_name}" whose ".metadata" does not '
f"match that of the other submesh-cubes : "
f"{sub_metadata} != {indexcoord_metadata}."
)
if err:
raise ValueError(err)
# Use the mesh_dim to transpose inputs + outputs, if required, as it is
# simpler for all the array operations to always have the mesh dim *last*.
if mesh_dim == mesh_cube.ndim - 1:
# Mesh dim is already the last one : no tranpose required
untranspose_dims = None
else:
dim_range = np.arange(mesh_cube.ndim, dtype=int)
# Transpose all inputs to mesh-last order
tranpose_dims = [i_dim for i_dim in dim_range if i_dim != mesh_dim] + [
mesh_dim
] # chop out mesh_dim + put it at the end
def transposed_copy(cube, dim_order):
cube = cube.copy()
cube.transpose(dim_order)
return cube
mesh_cube = transposed_copy(mesh_cube, tranpose_dims)
submesh_cubes = [
transposed_copy(region_cube, tranpose_dims)
for region_cube in submesh_cubes
]
# Also prepare for transforming the output back to the original order
untranspose_dims = dim_range.copy()
# Neat trick to produce the reverse operation
untranspose_dims[tranpose_dims] = dim_range
#
# Here's the core operation..
#
def fill_region(target, regiondata, regioninds):
if not target.flags.writeable:
# The initial input can be a section of a da.zeros(), which has no
# real array "behind" it. This means that real arrays created in
# memory are only chunk-sized, but it also means that 'target' may
# not be writeable. So take a copy to fix that, where needed.
target = target.copy()
# N.B. Indices are basically 1D, but may have leading *1 dims for
# alignment, to satisfy da.map_blocks
assert all(size == 1 for size in regioninds.shape[:-1])
inds = regioninds.flatten()
# Assign blocks with indexing on the last dim only
target[..., inds] = regiondata
return target
# Create an initially 'empty' (all-masked) dask array matching the input.
# N.B. this does not use the mesh_cube.lazy_data() array, but only its
# shape and dtype, since the data itself is not used in the calculation.
# N.B. chunking matches the input cube, allowing performance control.
input_data = mesh_cube.lazy_data()
result_array = da.ma.masked_array(
da.zeros(
input_data.shape,
dtype=result_dtype,
chunks=input_data.chunksize,
),
True,
)
# Wrap this repeatedly with a lazy operation to assign each region.
# It is done this way because we couldn't get map_blocks to correctly wrap
# a function which does all regions in a single operation.
# TODO: replace with a single-stage solution: Probably better, if possible.
# Notes on resultant calculation properties:
# 1. map_blocks is chunk-mapped, so it is parallelisable and space-saving
# 2. However, fetching less than a whole chunk is not efficient
for cube in submesh_cubes:
# Lazy data array from the region cube
sub_data = cube.lazy_data()
# Lazy indices from the mesh-dim coord
mesh_dimcoord = cube.coord(
name_or_coord=index_coord_name, dimensions=cube.ndim - 1
)
indarr = mesh_dimcoord.lazy_points()
# Extend indarr dimensions to align it with the 'target' array dims
assert indarr.ndim == 1
shape = (1,) * (cube.ndim - 1) + indarr.shape
indarr = indarr.reshape(shape)
# Apply the operation to paste from one region into the target
# N.B. replacing 'result_array' each time around the loop
result_array = da.map_blocks(
fill_region,
result_array,
sub_data,
indarr,
dtype=result_array.dtype,
meta=np.ndarray,
)
# Construct the result cube
result_cube = mesh_cube.copy()
result_cube.data = result_array
# Copy names, units + attributes from region data (N.B. but not var_name)
result_cube.metadata = result_metadata
if untranspose_dims is not None:
# Re-order dims as in the original input
result_cube.transpose(untranspose_dims)
return result_cube
```