healpix_geo.auto.bilinear_interpolation#

healpix_geo.auto.bilinear_interpolation(longitude, latitude, grid, *, num_threads=0)#

Get the cell ids and weights necessary to bilinearly interpolate the given values.

Parameters:

longitude (numpy.ndarray) – The longitudes of the input points, in degrees.
latitude (numpy.ndarray) – The latitudes of the input points, in degrees.
grid (Grid) – The definition of the HEALPix grid.
num_threads (int, optional) – Specifies the number of threads to use for the computation. Default to 0 means it will choose the number of threads based on the RAYON_NUM_THREADS environment variable (if set), or the number of logical CPUs (otherwise)

Returns:

cell_ids (numpy.ndarray) – The neighbours above and below the given points as a \(N\) x \(4\) masked array.
weights (numpy.ndarray) – The associated weights as a \(N\) x \(4\) masked array.

Raises:

ValueError – When the HEALPix cell indexes given have values out of \([0, 4^{29 - depth})\).

Examples

>>> import healpix_geo.auto as hg
>>> import numpy as np

Define the grid

>>> grid = hg.Grid(level=12, indexing_scheme="nested", ellipsoid="sphere")
>>> grid
Grid(level=12, indexing_scheme='nested', ellipsoid='sphere')

Define coordinates

>>> lon = np.array([-15.0, -10.0, -5.0, 0.0, 5.0], dtype="float64")
>>> lat = np.array([30.0, 35.0, 40.0, 45.0, 50.0], dtype="float64")

Compute interpolation weights

>>> cell_ids, weights = hg.bilinear_interpolation(lon, lat, grid)
>>> cell_ids
MArray(
    array([[54892952, 54892953, 54892954, 54892955],
           [55675332, 55675333, 55675334, 55675335],
           [55890822, 55890823, 55890828, 55890829],
           [11206655, 11250346, 55967743, 56055125],
           [11481364, 11481365, 11481366, 11481367]], dtype=uint64),
    array([[False, False, False, False],
           [False, False, False, False],
           [False, False, False, False],
           [False, False, False, False],
           [False, False, False, False]])
)
>>> weights
MArray(
    array([[0.13888889, 0.69444444, 0.02777778, 0.13888889],
           [0.21156076, 0.15051566, 0.37273788, 0.2651857 ],
           [0.12397948, 0.17692801, 0.28803912, 0.4110534 ],
           [0.00248345, 0.49751655, 0.00248345, 0.49751655],
           [0.0540781 , 0.08623943, 0.33131993, 0.52836254]]),
    array([[False, False, False, False],
           [False, False, False, False],
           [False, False, False, False],
           [False, False, False, False],
           [False, False, False, False]])
)