nside2npix

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

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

FORMAT

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

QUALIFIERS

Nside

HEALPix resolution parameter (integer, scalar or not), should be a valid N_side (power of 2 $\le 2^{29}$)

Npix

number of pixels, same size as Nside, N_pix= 12 N_side² if N_side 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.

/HELP

if set on input, the documentation header is printed, and the routine exits (with a returned value of -1 and an error flag set to 0).

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_pix= 12N_side².

RELATED ROUTINES

This section lists the routines related to nside2npix

idl

version 6.4 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