npix2nside

This IDL facility provides the HEALPix resolution parameter Nside corresponding to Npix pixels over the full sky.

Location in HEALPix directory tree: src/idl/toolkit/npix2nside.pro 

FORMAT

IDL> Nside=NPIX2NSIDE (Npix [, ERROR=])

QUALIFIERS

Npix

number of pixels over the full sky (scalar integer), should be a valid Npix ( N_pix= 12N_side² with N_side power of 2 in $\{1,\ldots,2^{29}\}$)

Nside

on output: resolution parameter if Npix is valid, -1 otherwise

KEYWORDS

ERROR=

error flag, set to 1 on output if Npix is NOT valid, or stays to 0 otherwise.

DESCRIPTION

npix2nside checks that the given Npix is valid ( N_pix= 12N_side² with N_side a power of 2 in $\{1,\ldots,2^{29}\}$) and then computes the corresponding resolution parameter N_side.

RELATED ROUTINES

This section lists the routines related to npix2nside

idl

version 6.4 or more is necessary to run npix2nside .

nside2npix

computes Npix corresponding to Nside

pix2xxx, ang2xxx, vec2xxx, ...

conversion between vector or angles and pixel index and vice-versa

vec2pix, pix2vec

conversion between vector and pixel index

nest2ring, ring2nest

conversion between NESTED and RING indices

EXAMPLE:

Nside = npix2nside(49152, ERROR=error)

Nside will be 64 because 49152 is a valid pixel number (=12*64² and 64 is a power of 2), and error will be 0

EXAMPLE:

Nside = npix2nside(49151, ERROR=error)

Nside will be -1 and error: 1, because 49151 is not a valid number of HEALPix pixels over the full sky.