# xy2pix

Find (nest indexed) MEALPix pixel number corresponding to a pixel index on a HEALPix face

## Contents

- Syntax
- Input Arguments
- Return Arguments
- Description
- Example
- See also

## Syntax

ipix = xy2pix(nSide, ix, iy, nFace)

## Input Arguments

    nside     HEALPix resolution parameter (power of 2)
    ix,iy     integer pixel location on face (1 <= ix, iy <= nSide)
    nFace     HEALPix face  number (1 <= nFace <= 12)

One or both ix and iy may be scalars. If neither is a scalar both must have the same size.

## Return Arguments

    ipix      NESTED pixel index for given x,y on the face

## Description

At lowest resolution HEALPix divides the sphere into 12 faces, each with its own coordinate system. Each face is further subdivided in a regular fashion as the resolution parameter is increased. Given a face number (from 1 to 12), a resolution parameter, and a location on the face XY2PIX identifies the pixel number (in the nested indexing scheme).

## Example

    nSide = 4;
    nFace = 3;
    ix = [1 2; 1 2];
    iy = [1 1; 2 2];
    nPix = xy2pix(nSide,ix,iy,nFace)

    nPix =

        49    50
        51    52

## See also

pix2xy

Copyright 2010-2011 Lee Samuel Finn. Terms of Use.