WCSGeometry

class hips.WCSGeometry(wcs: astropy.wcs.wcs.WCS, width: int, height: int)

Bases: object

Sky image geometry: WCS and image shape.

Parameters:

wcs : WCS

WCS projection object

width, height : int

Width and height of the image in pixels

Examples

To create a WCSGeometry, you can create any WCS and choose an image shape (number of pixels):

from astropy.wcs import WCS
from hips import WCSGeometry
wcs = WCS(naxis=2)
wcs.wcs.ctype[0] = 'GLON-AIT'
wcs.wcs.ctype[1] = 'GLAT-AIT'
wcs.wcs.crval[0] = 0
wcs.wcs.crval[1] = 0
wcs.wcs.crpix[0] = 1000
wcs.wcs.crpix[1] = 500
wcs.wcs.cdelt[0] = -0.01
wcs.wcs.cdelt[1] = 0.01
geometry =  WCSGeometry(wcs, width=2000, height=1000)

See also WCSGeometry.create as a simpler (but also not quite as flexible) way to generate WCS and WCSGeometry objects.

Attributes Summary

WCS_ORIGIN_DEFAULT	Default WCS transform origin, to be used in all WCS pix <-> world calls.
celestial_frame	Celestial frame for the given WCS (str).
center_pix	Image center in pixel coordinates (tuple of x, y).
center_skycoord	Image center in sky coordinates (SkyCoord).
fits_header	FITS header for the given WCS (Header).
pixel_skycoords	Grid of sky coordinates of the image pixels (SkyCoord).

Methods Summary

create(skydir, width, height, fov, …)	Create WCS object for given sky image parameters (WCSGeometry).
create_from_dict(params)	Create WCS object from a dictionary (WCSGeometry).
make(geometry, _ForwardRef()])	Convenience constructor for create_from_dict classmethod or existing object (WCSGeometry).
pix_to_sky(x, y)	Helper function to convert pix to sky coordinates.

Attributes Documentation

WCS_ORIGIN_DEFAULT = 0

Default WCS transform origin, to be used in all WCS pix <-> world calls.

celestial_frame

Celestial frame for the given WCS (str).

Calls wcs_to_celestial_frame.

center_pix

Image center in pixel coordinates (tuple of x, y).

center_skycoord

Image center in sky coordinates (SkyCoord).

fits_header

FITS header for the given WCS (Header).

pixel_skycoords

Grid of sky coordinates of the image pixels (SkyCoord).

Methods Documentation

classmethod create(skydir: astropy.coordinates.sky_coordinate.SkyCoord, width: int, height: int, fov: Union[str, astropy.coordinates.angles.Angle], coordsys: str = 'icrs', projection: str = 'AIT') → hips.utils.wcs.WCSGeometry

Create WCS object for given sky image parameters (WCSGeometry).

Parameters:

skydir : SkyCoord

Sky coordinate of the WCS reference point

width, height : int

Width and height of the image in pixels

fov : str or Angle

Field of view

coordsys : {‘icrs’, ‘galactic’}

Coordinate system

projection : str

Projection of the WCS object. To see list of supported projections visit: http://docs.astropy.org/en/stable/wcs/#supported-projections

Examples

>>> from astropy.coordinates import SkyCoord
>>> from hips import WCSGeometry
>>> skycoord = SkyCoord(10, 20, unit='deg')
>>> geometry = WCSGeometry.create(
...     skydir=SkyCoord(0, 0, unit='deg', frame='galactic'),
...     width=2000, height=1000, fov='3 deg',
...     coordsys='galactic', projection='AIT',
... )
>>> geometry.wcs
Number of WCS axes: 2
CTYPE : 'GLON-AIT'  'GLAT-AIT'
CRVAL : 0.0  0.0
CRPIX : 500.0  1000.0
PC1_1 PC1_2  : 1.0  0.0
PC2_1 PC2_2  : 0.0  1.0
CDELT : -0.0015  0.0015
NAXIS : 0  0
>>> geometry.shape
Shape(width=2000, height=1000)

classmethod create_from_dict(params: dict) → hips.utils.wcs.WCSGeometry

Create WCS object from a dictionary (WCSGeometry).

The extra options are passed to the create class method, it can take the following parameters:

• target
• width
• height
• fov
• coordsys
• projection

For detailed description, see the create class method’s docstring.

classmethod make(geometry: Union[dict, _ForwardRef('WCSGeometry')]) → hips.utils.wcs.WCSGeometry

Convenience constructor for create_from_dict classmethod or existing object (WCSGeometry).

pix_to_sky(x, y) → astropy.coordinates.sky_coordinate.SkyCoord

Helper function to convert pix to sky coordinates.