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neighbours_nest
This subroutine returns the number and locations (in terms of pixel
numbers) of the topological neighbours of a central pixel. The pixels
are ordered in a clockwise sense about the central pixel with the
southernmost pixel in first element. For the 4 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/f90/mod/pix_tools.f90
FORMAT call neighbours_nest(
nside, ipix, list, nneigh
)
ARGUMENTS
| name & dimensionality |
kind |
in/out |
description |
|---|
| |
|
|
|
|
nside |
I4B |
IN |
The Nside parameter of the map. |
| ipix |
I4B |
IN |
The pixel number of the central pixel. |
| list(8) |
I4B |
OUT |
On exit, the vector of neighbouring pixels. This
contains nneigh relevant elements. |
| nneigh |
I4B |
OUT |
The number of neighbours (mostly 8, except at
8 sites, where there are only 7 neighbours). |
EXAMPLE:
use pix_tools
integer :: n, list(1:8)
call neighbours_nest(4, 1, list, nneigh)
print*,nneigh
print*,list(1:nneigh)
This returns nneigh=8 and a vector list, which contains the pixel
numbers ( 90, 0, 2, 3, 6, 4, 94, 91).
MODULES & ROUTINESThis section lists the modules and routines used by neighbours_nest.
-
mk_xy2pix, mk_pix2xy
- precomputing arrays for the conversion
of NESTED pixel numbers to Cartesian coords in each face.
-
pix2xy_nest, xy2pix_nest
- Conversion between NESTED pixel numbers to Cartesian coords in each face.
-
bit_manipulation
- module, containing:
-
invMSB, invLSB,swapLSBMSB,invswapLSBMSB
- functions which manipulate the bit vector which
represents the NESTED pixel numbers. They correspond to
NorthWest<->SouthEast, SouthWest<->NorthEast, East<->West and
North-South flips of the diamond faces, respectively.
RELATED ROUTINESThis section lists the routines related to neighbours_nest
-
pix2ang, ang2pix
- convert between angle and pixel number.
-
pix2vec, vec2pix
- convert between a cartesian vector and pixel number.
Eric Hivon
2010-06-18
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