WCS

class sherpa.astro.io.wcs.WCS(name: str, type: str, crval: Sequence[float] | ndarray, crpix: Sequence[float] | ndarray, cdelt: Sequence[float] | ndarray, crota: float = 0.0, epoch: float = 2000.0, equinox: float = 2000.0)

Bases: NoNewAttributesAfterInit

Represent a World Coordinate System transformation.

This does not support all possible astronomical transforms.

Parameters:

• name – The name of the transformation (expected to be “world” or “physical”).

• type – The transform type (expected to be one of “LINEAR”, “WCS”, or “TAN-P”).

• crval – The reference point in the output coordinate system (a two-element sequence).

• crpix – The reference point in the input coordinate system (a two-element sequence).

• cdelt – The width and height of a pixel in the output coordinate system (a two-element sequence).

• crota – The rotation of the transformation.

• epoch – The epoch of the transformation (not always used).

• equinox – The equinox of the transformation (not always used).

Methods Summary

apply(-> tuple[~numpy.float64, ~numpy.float64])	Convert the input coordinates to the output system.
invert(-> tuple[~numpy.float64, ~numpy.float64])	Convert the output coordinates to the input system.

Methods Documentation

apply(x0: float, x1: float) → tuple[float64, float64]

apply(x0: Sequence[float] | ndarray, x1: Sequence[float] | ndarray) → tuple[ndarray, ndarray]

Convert the input coordinates to the output system.

Parameters:

• x0 – Coordinate or coordinates of the first axis.

• x1 – Coordinate or coordinates of the second axis (must match the size of x0).

Returns:

The coordinate (or coordinates) of the points in the output system as the two-element tuple (c0, c1). If x0 and x1 are scalars then c0 and c1 will be scalars otherwise they will be arrays.

Return type:

retval

Examples

>>> crval = [200, -100]
>>> crpix = [5, 10]
>>> cdelt = [2, 4]
>>> c1 = WCS("physical", "LINEAR", crval, crpix, cdelt)
>>> x, y = c1.apply(5, 10)
>>> float(x), float(y)
(200.0, -100.0)
>>> c1.apply([5, 10], [10, 2])
(array([200., 210.]), array([-100., -132.]))

invert(x0: float, x1: float) → tuple[float64, float64]

invert(x0: Sequence[float] | ndarray, x1: Sequence[float] | ndarray) → tuple[ndarray, ndarray]

Convert the output coordinates to the input system.

Parameters:

• x0 – Coordinate or coordinates of the first axis.

• x1 – Coordinate or coordinates of the second axis (must match the size of x0).

Returns:

The coordinate (or coordinates) of the points in the input system as the two-element tuple (c0, c1). If x0 and x1 are scalars then c0 and c1 will be scalars otherwise they will be arrays.

Return type:

retval

Examples

>>> crval = [200, -100]
>>> crpix = [5, 10]
>>> cdelt = [2, 4]
>>> c1 = WCS("physical", "LINEAR", crval, crpix, cdelt)
>>> x, y = c1.invert(200, -100)
>>> float(x), float(y)
(5.0, 10.0)
>>> c1.invert([200, 210], [-100, -132])
(array([ 5., 10.]), array([10.,  2.]))