pix2xxx,ang2xxx,vec2xxx, nest2ring,ring2nest

The Fortran90 module pix_tools contains some subroutines to convert between pixel number in the HEALPix map and $(\theta,\phi)$ or $(x,y,z)$ coordinates on the sphere. Some of these routines are listed here.

Location in HEALPix directory tree: src/f90/mod/pix_tools.F90 

ARGUMENTS

name & dimensionality	kind	in/out	description
nside	I4B	IN	$N_{\mathrm{side}}$ parameter for the HEALPix map.
ipnest	I4B/ I8B	—	pixel identification number in NESTED scheme over the range {0, $N_{\mathrm{pix}}-1$}.
ipring	I4B/ I8B	—	pixel identification number in RING scheme over the range {0, $N_{\mathrm{pix}}-1$}.
theta	DP	—	colatitude in radians measured southward from north pole in {0,$\pi$}.
phi	DP	—	longitude in radians, measured eastward in $[0,\ 2\pi]$.
vector(3)	DP	—	three dimensional cartesian position vector $(x,y,z)$. The north pole is $(0,0,1)$. An output vector is normalised to unity.
vertex(3,4) OPTIONAL	DP	OUT	three dimensional cartesian position vectors $(x,y,z)$ (normalised to unity) pointing to the 4 vertices of a given pixel. The four vertices are listed in the order North, West, South, East.

ROUTINES:
call pix2ang_ring(nside, ipring, theta, phi)

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

call pix2vec_ring(nside, ipring, vector [,vertex])

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.

call ang2pix_ring(nside, theta, phi, 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.

call vec2pix_ring(nside, vector, 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.

call pix2ang_nest(nside, ipnest, theta, phi)

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

call pix2vec_nest(nside, ipnest, vector [,vertex])

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.

call ang2pix_nest(nside, theta, phi, 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.

call vec2pix_nest(nside, vector, 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 .

call nest2ring(nside, ipnest, ipring)

performs conversion from NESTED to RING pixel number.

call ring2nest(nside, ipring, 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

neighbours_nest

find neighbouring pixels.

ang2vec

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

vec2ang

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

convert_inplace

in-place conversion between RING and NESTED for integer/real/double maps.

convert_nest2ring

convert from NESTED to RING scheme using a temporary array.

nest2uniq, uniq2nest

conversion of standard pixel index to/from Unique ID number