Healpix#

class cygrid.Healpix(uint64_t nside=1, uint32_t scheme=RING)#

Bases: object

Helper class for HEALPix operations.

Implements conversion between HEALPix world and pixel coordinates (‘RING’ representation only). Also provides a query_disc method that returns a disc footprint for \(\varphi = 180^\circ\) for a given ring.

Parameters:

nsideunsigned 64-bit int: The HEALPix nside parameter.
schemeenum: The HEALPix scheme. Currently, only ‘RING’ is supported.

Notes

Attributes Summary

`ncap`	property ncap : unsigned 64-bit int
`npface`	property nface : unsigned 64-bit int
`npix`	property npix : unsigned 64-bit int
`nrings`	property nrings : unsigned 64-bit int
`nside`	property nside : unsigned 64-bit int
`omega`	property omega : double
`order`	property order : unsigned 64-bit int
`resolution`	property resolution : double
`scheme`	property scheme : enum

Methods Summary

`ang2pix`(self, double theta, double phi)	Return the pixel index containing the angular coordinates \((\varphi, \vartheta)\).
`ang2pix_many`(self, double[, double[)	Return the pixel indices containing the angular coordinates of \((\varphi, \vartheta)\) arrays.
`get_ring_info_small`(self, uint64_t ring)	Return start index and number of pixels per healpix ring.
`pix2ang`(self, uint64_t pix)	Convert HEALPix index to angular coordinates \((\varphi, \vartheta)\).
`pix2ang_many`(self, long[)	Convert HEALPix indices to angular coordinates of \((\varphi, \vartheta)\) arrays.
`pix2ring`(self, uint64_t pix)	Return 'ring' number that contains the HEALPix pixel, 'pix'.
`pix2ring_many`(self, long[)	Return 'ring' numbers containing HEALPix pixels given in array, 'pix'.
`query_disc`(self, double theta, double phi, ...)	Return hpx indices of a disc around \((\vartheta, \varphi)\).
`query_disc_phi180`(self, ...)	Return HEALPix indices of a disc around \(\varphi=180^\circ\) for 'disc_ring'.

Attributes Documentation

ncap#

property ncapunsigned 64-bit int: Return the HEALPix ‘ncap’ parameter.

npface#

property nfaceunsigned 64-bit int: Return the HEALPix ‘nface’ parameter.

npix#

property npixunsigned 64-bit int: Return the HEALPix ‘npix’ parameter.

nrings#

property nringsunsigned 64-bit int: Return the HEALPix ‘nrings’ parameter.

nside#

property nsideunsigned 64-bit int: The HEALPix ‘nside’ parameter. (Re-)setting ‘nside’ updates other properties.

omega#

property omegadouble: Return the solid angle, ‘omega’ of the HEALPix pixels for current nside.

order#

property orderunsigned 64-bit int: Return the HEALPix ‘order’ parameter.

resolution#

property resolutiondouble: Return the angular size of the HEALPix pixels for current nside.

scheme#

property schemeenum: The HEALPix ‘scheme’. Currently only ‘RING’ is supported.

Methods Documentation

ang2pix(self, double theta, double phi)#

Return the pixel index containing the angular coordinates \((\varphi, \vartheta)\).

Wrapper around the Cython-only (private) method _ang2pix.

Parameters:

thetadouble: \(\vartheta\) coordinate (\(\vartheta = \pi/2 - \mathrm{latitude}\)).
phidouble: \(\varphi\) coordinate (longitude).

Returns:

pixunsigned 64-bit int: The HEALPix pixel index.

Raises:

ValueError: Invalid theta value.

ang2pix_many(self, double[::1] theta, double[::1] phi)#

Return the pixel indices containing the angular coordinates of \((\varphi, \vartheta)\) arrays.

Wrapper around the Cython-only (private) method _ang2pix.

Parameters:

thetaarray of doubles: \(\vartheta\) coordinate (\(\vartheta = \pi/2 - \mathrm{latitude}\)).
phiarray of doubles: \(\varphi\) coordinate (longitude).

Returns:

pixarray of unsigned 64-bit int: The HEALPix pixel index.

get_ring_info_small(self, uint64_t ring)#

Return start index and number of pixels per healpix ring.

Wrapper around the Cython-only (private) method _get_ring_info_small.

Parameters:

ringunsigned 64-bit int: The HEALPix ring parameter to get information on.

Returns:

startpixunsigned 64-bit int: The HEALPix index of the first pixel in ring.
num_pix_in_ringunsigned 64-bit int: The number of HEALPix pixels in ring.
shiftedbool: Whether the central HEALPix pixel in that ring is shifted from \(\varphi=180^\circ\).

Raises:

ValueError: Ring index not in valid range.

pix2ang(self, uint64_t pix)#

Convert HEALPix index to angular coordinates \((\varphi, \vartheta)\).

Wrapper around the Cython-only (private) method _pix2ang.

Parameters:

pixunsigned 64-bit int: The HEALPix pixel index.

Returns:

thetadouble: \(\vartheta\) coordinate (\(\vartheta = \pi/2 - \mathrm{latitude}\)).
phidouble: \(\varphi\) coordinate (longitude).

Raises:

ValueError: pix not in valid range.

pix2ang_many(self, long[::1] pix)#

Convert HEALPix indices to angular coordinates of \((\varphi, \vartheta)\) arrays.

Wrapper around the Cython-only (private) method _pix2ang.

Parameters:

pixarray of unsigned 64-bit int: The HEALPix pixel index.

Returns:

thetaarray of doubles: \(\vartheta\) coordinate (\(\vartheta = \pi/2 - \mathrm{latitude}\)).
phiarray of doubles: \(\varphi\) coordinate (longitude).

pix2ring(self, uint64_t pix)#

Return ‘ring’ number that contains the HEALPix pixel, ‘pix’.

Wrapper around the Cython-only (private) method _pix2ring.

Parameters:

pixunsigned 64-bit int: The HEALPix index.

Returns:

ringunsigned 64-bit int: The HEALPix ring.

Raises:

ValueError: Pixel index not in valid range.

pix2ring_many(self, long[::1] pix)#

Return ‘ring’ numbers containing HEALPix pixels given in array, ‘pix’.

Wrapper around the Cython-only (private) method _pix2ring.

Parameters:

pixarray of unsigned 64-bit int: The HEALPix indices.

Returns:

ringarray of unsigned 64-bit int: The HEALPix rings.

query_disc(self, double theta, double phi, double disc_size_rad)#

Return hpx indices of a disc around \((\vartheta, \varphi)\).

This uses query_disc_phi180 and shifts the pixels along ring.

Wrapper around the cython-only (private) method _query_disc.

Parameters:

theta/phidouble: Coordinates \((\vartheta, \varphi)\) in radians.
disc_size_raddouble: Size of the disc in radians.

Returns:

disc_indicesarray of unsigned 64-bit int: The HEALPix indices of the disc.

query_disc_phi180(self, double disc_size_rad, uint64_t disc_ring)#

Return HEALPix indices of a disc around \(\varphi=180^\circ\) for ‘disc_ring’.

This is a modified version of the HEALPix library query_disc routine that returns the HEALPix indices of a disc around arbitrary coordinates. Here, it was modified to only work for coordinates having \(\varphi=180^\circ\) and a \(\vartheta\) that coincides with the latitude of a HEALPix ring. These discs can be shifted along \(\varphi\) - which is faster than calling query_disc if one cashes the \(\varphi=180^\circ\) discs.

Wrapper around the Cython-only (private) method _query_disc_phi180.

Parameters:

disc_size_raddouble: Size of the disc in radians.
disc_ringunsigned 64-bit int: HEALPix ring index of the requested disc center.

Returns:

disc_indicesarray of unsigned 64-bit int: The HEALPix indices of the disc.