healpix_geo.zuniq.kth_neighbourhood

healpix_geo.zuniq.kth_neighbourhood(ipix, ring, num_threads=0)

Get the kth ring neighbouring cells of some HEALPix cells.

This method returns a \(N\) x \((2 k + 1)^2\) np.uint64 numpy array containing the neighbours of each cell of the \(N\) sized ipix array. This method is wrapped around the kth_neighbourhood method from the cdshealpix Rust crate.

Parameters:

• ipix (numpy.ndarray) – The HEALPix cell indexes given as a np.uint64 numpy array.

• ring (int) – The number of rings. ring=0 returns just the input cell ids, ring=1 returns the 8 (or 7) immediate neighbours, ring=2 returns the 8 (or 7) immediate neighbours plus their immediate neighbours (a total of 24 cells), and so on.

• 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:

neighbours (numpy.ndarray) – A \(N\) x \((2 k + 1)^2\) np.int64 numpy array containing the kth ring neighbours of each cell. The \(5^{th}\) element corresponds to the index of HEALPix cell from which the neighbours are evaluated. All its 8 neighbours occup the remaining elements of the line.

Raises:

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

Examples

Try it in your browser!

>>> from healpix_geo.zuniq import kth_neighbourhood
>>> import numpy as np
>>> ipix = np.array([1460288880640, 223338299392, 360777252864], dtype="uint64")
>>> ring = 3
>>> neighbours = kth_neighbourhood(ipix, ring)
>>> neighbours
array([[      1460288880640, 2497997973430992896, 2497998042150469632,
        2498000997087969280,       4415226380288,       4449586118656,
              1494648619008,       1425929142272,       1391569403904,
        2497997732912824320, 2497997939071254528, 2497998007790731264,
        2498000962728230912, 2498001031447707648, 2498001065807446016,
        2497997767272562688,       4483945857024,       4518305595392,
              4621384810496,       4552665333760,       1597727834112,
              1529008357376,       1322849927168,       1219770712064,
              1185410973696, 2497997561114132480, 2497997629833609216,
        2497997835992039424, 2497997904711516160, 2498000859649015808,
        2498000928368492544, 2498001134526922752, 2498001237606137856,
        2498001271965876224, 2497997698553085952, 2497997664193347584,
              4690104287232,       4724464025600,       4827543240704,
              4861902979072,       4655744548864,       4587025072128,
              1632087572480,       1563368095744,       1357209665536,
              1288490188800,       1254130450432,       1151051235328,
              1116691496960],
       [       223338299392,         51539607552,        120259084288,
               326417514496,        429496729600,        463856467968,
               257698037760,        188978561024,        154618822656,
        3266610923992776704, 3266611473748590592, 3266611095791468544,
        3266611061431730176, 3266610958352515072,         17179869184,
                85899345920,        292057776128,        360777252864,
               395136991232,        498216206336,        532575944704,
               910533066752,        841813590016,        635655159808,
               566935683072, 5188146684831465472, 5188146753550942208,
        2497996599041458176, 2497996667760934912, 2497996873919365120,
        2497996942638841856, 2497997698553085952, 3266611508108328960,
        3266611439388852224, 3266611405029113856, 3266611027071991808,
        3266610992712253440, 3266610889633038336, 3266610855273299968,
              1116691496960,       1151051235328,       1254130450432,
              1288490188800,       1666447310848,       1700807049216,
               944892805120,        876173328384,        670014898176,
               601295421440],
       [       360777252864, 2497996873919365120, 2497996942638841856,
        2497997698553085952,       1116691496960,       1151051235328,
               395136991232,        326417514496,        292057776128,
        2497996633401196544, 2497996839559626752, 2497996908279103488,
        2497997664193347584, 2497997732912824320, 2497997767272562688,
        2497996667760934912,       1185410973696,       1219770712064,
              1322849927168,       1254130450432,        498216206336,
               429496729600,        223338299392,        120259084288,
                85899345920, 2497996461602504704, 2497996530321981440,
        2497996736480411648, 2497996805199888384, 2497997561114132480,
        2497997629833609216, 2497997835992039424, 2497997939071254528,
        2497997973430992896, 2497996599041458176, 2497996564681719808,
              1391569403904,       1425929142272,       1529008357376,
              1563368095744,       1357209665536,       1288490188800,
               532575944704,        463856467968,        257698037760,
               188978561024,        154618822656,         51539607552,
                17179869184]])

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