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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 ROUTINESThis section lists the routines related to neighbours_ring
-
idl
- version 6.1 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,
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query_strip, query_triangle
- render the list of pixels enclosed
respectively in a given disc, polygon, latitude strip and triangle
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nest2ring, ring2nest
- conversion between NESTED and RING indices
EXAMPLE:
will return:8 16 6 5 0 3 2 8 7
listing the RING-indexed 8 neighbors of pixel #1 for Nside=4
Eric Hivon
2010-06-18
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