# Source code for verde.mask

```
"""
Mask grid points based on different criteria.
"""
import numpy as np
# pylint doesn't pick up on this import for some reason
from scipy.spatial import Delaunay # pylint: disable=no-name-in-module
from .base.utils import n_1d_arrays, check_coordinates
from .utils import kdtree
[docs]def distance_mask(
data_coordinates, maxdist, coordinates=None, grid=None, projection=None
):
"""
Mask grid points that are too far from the given data points.
Distances are Euclidean norms. If using geographic data, provide a
projection function to convert coordinates to Cartesian before distance
calculations.
Either *coordinates* or *grid* must be given:
* If *coordinates* is not None, produces an array that is False when a
point is more than *maxdist* from the closest data point and True
otherwise.
* If *grid* is not None, produces a mask and applies it to *grid* (an
:class:`xarray.Dataset`).
.. note::
If installed, package ``pykdtree`` will be used instead of
:class:`scipy.spatial.cKDTree` for better performance.
Parameters
----------
data_coordinates : tuple of arrays
Same as *coordinates* but for the data points.
maxdist : float
The maximum distance that a point can be from the closest data point.
coordinates : None or tuple of arrays
Arrays with the coordinates of each point that will be masked. Should
be in the following order: (easting, northing, ...). Only easting and
northing will be used, all subsequent coordinates will be ignored.
grid : None or :class:`xarray.Dataset`
2D grid with values to be masked. Will use the first two dimensions of
the grid as northing and easting coordinates, respectively. For this to
work, the grid dimensions **must be ordered as northing then easting**.
The mask will be applied to *grid* using the
:meth:`xarray.Dataset.where` method.
projection : callable or None
If not None, then should be a callable object ``projection(easting,
northing) -> (proj_easting, proj_northing)`` that takes in easting and
northing coordinate arrays and returns projected easting and northing
coordinate arrays. This function will be used to project the given
coordinates (or the ones extracted from the grid) before calculating
distances.
Returns
-------
mask : array or :class:`xarray.Dataset`
If *coordinates* was given, then a boolean array with the same shape as
the elements of *coordinates*. If *grid* was given, then an
:class:`xarray.Dataset` with the mask applied to it.
Examples
--------
>>> from verde import grid_coordinates
>>> region = (0, 5, -10, -4)
>>> spacing = 1
>>> coords = grid_coordinates(region, spacing=spacing)
>>> mask = distance_mask((2.5, -7.5), maxdist=2, coordinates=coords)
>>> print(mask)
[[False False False False False False]
[False False True True False False]
[False True True True True False]
[False True True True True False]
[False False True True False False]
[False False False False False False]
[False False False False False False]]
>>> # Mask an xarray.Dataset directly
>>> import xarray as xr
>>> coords_dict = {"easting": coords[0][0, :], "northing": coords[1][:, 0]}
>>> data_vars = {"scalars": (["northing", "easting"], np.ones(mask.shape))}
>>> grid = xr.Dataset(data_vars, coords=coords_dict)
>>> masked = distance_mask((3.5, -7.5), maxdist=2, grid=grid)
>>> print(masked.scalars.values)
[[nan nan nan nan nan nan]
[nan nan nan 1. 1. nan]
[nan nan 1. 1. 1. 1.]
[nan nan 1. 1. 1. 1.]
[nan nan nan 1. 1. nan]
[nan nan nan nan nan nan]
[nan nan nan nan nan nan]]
"""
coordinates, shape = _get_grid_coordinates(coordinates, grid)
if projection is not None:
data_coordinates = projection(*n_1d_arrays(data_coordinates, 2))
coordinates = projection(*n_1d_arrays(coordinates, 2))
tree = kdtree(data_coordinates[:2])
distance = tree.query(np.transpose(n_1d_arrays(coordinates, 2)))[0].reshape(shape)
mask = distance <= maxdist
if grid is not None:
return grid.where(mask)
return mask
[docs]def convexhull_mask(
data_coordinates, coordinates=None, grid=None, projection=None,
):
"""
Mask grid points that are outside the convex hull of the given data points.
Either *coordinates* or *grid* must be given:
* If *coordinates* is not None, produces an array that is False when a
point is outside the convex hull and True otherwise.
* If *grid* is not None, produces a mask and applies it to *grid* (an
:class:`xarray.Dataset`).
Parameters
----------
data_coordinates : tuple of arrays
Same as *coordinates* but for the data points.
coordinates : None or tuple of arrays
Arrays with the coordinates of each point that will be masked. Should
be in the following order: (easting, northing, ...). Only easting and
northing will be used, all subsequent coordinates will be ignored.
grid : None or :class:`xarray.Dataset`
2D grid with values to be masked. Will use the first two dimensions of
the grid as northing and easting coordinates, respectively. For this to
work, the grid dimensions **must be ordered as northing then easting**.
The mask will be applied to *grid* using the
:meth:`xarray.Dataset.where` method.
projection : callable or None
If not None, then should be a callable object ``projection(easting,
northing) -> (proj_easting, proj_northing)`` that takes in easting and
northing coordinate arrays and returns projected easting and northing
coordinate arrays. This function will be used to project the given
coordinates (or the ones extracted from the grid) before calculating
distances.
Returns
-------
mask : array or :class:`xarray.Dataset`
If *coordinates* was given, then a boolean array with the same shape as
the elements of *coordinates*. If *grid* was given, then an
:class:`xarray.Dataset` with the mask applied to it.
Examples
--------
>>> from verde import grid_coordinates
>>> region = (0, 5, -10, -4)
>>> spacing = 1
>>> coords = grid_coordinates(region, spacing=spacing)
>>> data_coords = ((2, 3, 2, 3), (-9, -9, -6, -6))
>>> mask = convexhull_mask(data_coords, coordinates=coords)
>>> print(mask)
[[False False False False False False]
[False False True True False False]
[False False True True False False]
[False False True True False False]
[False False True True False False]
[False False False False False False]
[False False False False False False]]
>>> # Mask an xarray.Dataset directly
>>> import xarray as xr
>>> coords_dict = {"easting": coords[0][0, :], "northing": coords[1][:, 0]}
>>> data_vars = {"scalars": (["northing", "easting"], np.ones(mask.shape))}
>>> grid = xr.Dataset(data_vars, coords=coords_dict)
>>> masked = convexhull_mask(data_coords, grid=grid)
>>> print(masked.scalars.values)
[[nan nan nan nan nan nan]
[nan nan 1. 1. nan nan]
[nan nan 1. 1. nan nan]
[nan nan 1. 1. nan nan]
[nan nan 1. 1. nan nan]
[nan nan nan nan nan nan]
[nan nan nan nan nan nan]]
"""
coordinates, shape = _get_grid_coordinates(coordinates, grid)
n_coordinates = 2
# Make sure they are arrays so we can normalize
data_coordinates = n_1d_arrays(data_coordinates, n_coordinates)
coordinates = n_1d_arrays(coordinates, n_coordinates)
if projection is not None:
data_coordinates = projection(*data_coordinates)
coordinates = projection(*coordinates)
# Normalize the coordinates to avoid errors from qhull when values are very
# large (as occurs when projections are used).
means = [coord.mean() for coord in data_coordinates]
stds = [coord.std() for coord in data_coordinates]
data_coordinates = tuple(
(coord - mean) / std for coord, mean, std in zip(data_coordinates, means, stds)
)
coordinates = tuple(
(coord - mean) / std for coord, mean, std in zip(coordinates, means, stds)
)
triangles = Delaunay(np.transpose(data_coordinates))
# Find the triangle that contains each grid point.
# -1 indicates that it's not in any triangle.
in_triangle = triangles.find_simplex(np.transpose(coordinates))
mask = (in_triangle != -1).reshape(shape)
if grid is not None:
return grid.where(mask)
return mask
def _get_grid_coordinates(coordinates, grid):
"""
If coordinates is given, return it and their shape. Otherwise, get
coordinate arrays from the grid.
"""
if coordinates is None and grid is None:
raise ValueError("Either coordinates or grid must be given.")
if coordinates is None:
dims = [grid[var].dims for var in grid.data_vars][0]
coordinates = np.meshgrid(grid.coords[dims[1]], grid.coords[dims[0]])
check_coordinates(coordinates)
shape = coordinates[0].shape
return coordinates, shape
```