This IDL facility returns the number and indices of the topological immediate neighbours
of a central pixel. The pixels
are ordered in a clockwise sense (when watching the sphere from the outside)
about the central pixel with the
southernmost pixel in first element. For the four pixels in the southern
corners of the
equatorial faces which have two equally southern neighbours the
routine returns the southwestern pixel first and proceeds clockwise.
Location in HEALPix directory tree: src/idl/toolkit/neighbours_nest.pro
- HEALPix resolution parameter (scalar integer),
should be a valid Nside (power of 2)
- NESTED-scheme index of central pixel in [0,12*Nside2-1]
- output: list of neighbouring pixel (NESTED scheme index) of
- optional output: number of neighbours of pixel #Ipix0.
Usually 8, sometimes 7 (for 8 particular pixels) or 6 (if Nside=1)
neighbours_nest calls pix2xy_nest to find location of central pixel within the pixelation
base-face, and then xy2pix_nest to find neighbouring pixels within the same
face, or one of the bit manipulation routines if the neighbouring pixel
is on a different base-face.
This section lists the routines related to neighbours_nest
- version 6.4 or more is necessary to run neighbours_nest .
- returns topological immediate
neighbouring pixels of a given central pixel, using RING indexing.
- render the list of pixels enclosed
respectively in a given disc, polygon, latitude strip and triangle
- conversion between NESTED and RING indices
will return:8 90 0 2 3 6 4 94 91,
listing the NESTED-indexed 8 neighbors of pixel #1 for Nside=4
Version 3.31, 2017-01-06