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

Location in HEALPix directory tree: src/idl/toolkit/nside2npix.pro

FORMAT

IDL> Npix=NSIDE2NPIX (Nside [,ERROR=])

QUALIFIERS

Nside: HEALPix resolution parameter (scalar integer), should be a valid Nside (power of 2 $\le 2^{29}$ )
Npix: number of pixels, Npix = 12*Nside² if Nside is a valid resolution parameter or -1 otherwise

KEYWORDS

ERROR =: error flag, set to 1 on output if Nside is NOT valid, or stays to 0 otherwise.

DESCRIPTION

nside2npix checks that the given Nside is valid (power of 2 in $\{1,\ldots,2^{29}\}$ ) and then computes the corresponding number of pixels $N_{\rm pix} = 12N_{\rm side}^2$ .

RELATED ROUTINES

This section lists the routines related to nside2npix

idl: version 6.1 or more is necessary to run nside2npix .
npix2nside: computes Nside corresponding to Npix
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:

Npix = nside2npix(256, ERROR=error)

Npix will be 786432 the number of pixels over the full sky for the HEALPix resolution parameter 256 and error will be 0

EXAMPLE:

Npix = nside2npix(248, ERROR=error)

Npix will be -1 and error: 1, because 248 is not a valid value for a HEALPix resolution parameter

Eric Hivon 2010-06-18

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