neighbours_ring


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_ring.pro 


FORMAT

IDL> neighbours_ring (Nside, Ipix0, Listpix[,Nneigh])


QUALIFIERS

Nside
HEALPix resolution parameter (scalar integer), should be a valid Nside (power of 2)
Ipix0
RING-scheme index of central pixel in [0,12*Nside2-1]
Listpix
output: list of neighbouring pixel (RING scheme index) of size Nneigh
Nneigh
optional output: number of neighbours of pixel #Ipix0. Usually 8, sometimes 7 (for 8 particular pixels) or 6 (if Nside=1)


DESCRIPTION

neighbours_ring calls ring2nest, neighbours_nest and nest2ring


RELATED ROUTINES

This section lists the routines related to neighbours_ring

idl
version 6.4 or more is necessary to run neighbours_ring .
neighbours_nest
returns topological immediate neighbouring pixels of a given central pixel, using NESTED indexing.
query_disc, query_polygon,
query_strip, query_triangle
render the list of pixels enclosed respectively in a given disc, polygon, latitude strip and triangle
nest2ring, ring2nest
conversion between NESTED and RING indices


EXAMPLE:

neighbours_ring , 4, 1, list, nneigh
print,nneigh,list
will return:8 16 6 5 0 3 2 8 7 listing the RING-indexed 8 neighbors of pixel #1 for Nside=4

Version 3.31, 2017-01-06