These subroutines can be used to convert between pixel number in the HEALPix map and $(\theta,\phi)$ coordinates on the sphere. This is only a subset of the routines equivalent in Fortran90 or in IDL.

Location in HEALPix directory tree: src/C/subs/*.c

Note: These routines are based on the translation of the original F77 routines to C++ and then to C, by Reza Ansari (ansari@lal.in2p3.fr), Alex Kim (akim@lilys.lbl.gov), Guy Le Meur (lemeur@lal.in2p3.fr), Benoit Revenu (revenu@iap.fr) and Ken Ganga (kmg@ipac.caltech.edu).

ARGUMENTS

name & dimensionality	type	in/out	description

nside	long	IN	N_side parameter for the HEALPix map.
ipnest	long	--	pixel identification number in NESTED scheme over the range {0,N_pix-1}.
ipring	long	--	pixel identification number in RING scheme over the range {0,N_pix-1}.
theta	double	--	colatitude in radians measured southward from north pole in [0, $\pi$ ].
phi	double	--	longitude in radians, measured eastward in [0, $2\pi$ ].
vector	double	--	3D cartesian position vector (x,y,z). The north pole is (0,0,1). An output vector is normalised to unity.

ROUTINES:
void pix2ang_ring(long nside, long ipring, double *theta, double *phi);

renders theta and phi coordinates of the nominal pixel center given the pixel number ipring and a map resolution parameter nside.

void pix2vec_ring(long nside, long ipring, double *vector);

renders cartesian vector coordinates of the nominal pixel center given the pixel number ipring and a map resolution parameter nside. Optionally renders cartesian vector coordinates of the considered pixel four vertices.

void ang2pix_ring(long nside, double theta, double phi, long *ipring);

renders the pixel number ipring for a pixel which, given the map resolution parameter nside, contains the point on the sphere at angular coordinates theta and phi.

void vec2pix_ring(long nside, double *vector, long *ipring);

renders the pixel number ipring for a pixel which, given the map resolution parameter nside, contains the point on the sphere at cartesian coordinates vector.

void pix2ang_nest(long nside, long ipnest, double *theta, double *phi);

renders theta and phi coordinates of the nominal pixel center given the pixel number ipnest and a map resolution parameter nside.

void pix2vec_nest(long nside, long ipnest, double *vector);

renders cartesian vector coordinates of the nominal pixel center given the pixel number ipnest and a map resolution parameter nside. Optionally renders cartesian vector coordinates of the considered pixel four vertices.

void ang2pix_nest(long nside, double theta, double phi, long *ipnest);

renders the pixel number ipnest for a pixel which, given the map resolution parameter nside, contains the point on the sphere at angular coordinates theta and phi.

void vec2pix_nest(long nside, double *vector, long *ipnest)

renders the pixel number ipnest for a pixel which, given the map resolution parameter nside, contains the point on the sphere at cartesian coordinates vector .

void nest2ring(long nside, long ipnest, long *ipring);

performs conversion from NESTED to RING pixel number.

void ring2nest(long nside, long ipring, long *ipnest);

performs conversion from RING to NESTED pixel number.

MODULES & ROUTINES

This section lists the modules and routines used by pix2xxx, ang2xxx, vec2xxx, nest2ring, ring2nest.

mk_pix2xy, mk_xy2pix: routines used in the conversion between pixel values and ``cartesian'' coordinates on the Healpix face.

RELATED ROUTINES

This section lists the routines related to pix2xxx, ang2xxx, vec2xxx, nest2ring, ring2nest

ang2vec: convert $(\theta,\phi)$ spherical coordinates into (x,y,z) cartesian coordinates.
vec2ang: convert (x,y,z) cartesian coordinates into $(\theta,\phi)$ spherical coordinates.

Eric Hivon 2010-06-18

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These subroutines can be used to convert between pixel number in the HEALPix map and coordinates on the sphere. This is only a subset of the routines equivalent in Fortran90 or in IDL.