    Return information about the independent axes of a data set.

get_axes(id=None, bkg_id=None)
id - int or str, optional
bkg_id - int or str, optional

This function returns the coordinates of each point, or pixel, in the data set. The `get_indep` function may be be preferred in some situations.

For 1D data sets, the "alternate" view is the same as the independent axis:

>>> load_arrays(1, [10, 15, 19], [4, 5, 9], Data1D) >>> get_indep() array([10, 15, 19]) >>> get_axes() array([10, 15, 19])

For a PHA data set, the approximate energy grid of the channels is returned (this is determined by the EBOUNDS extension of the RMF).

>>> load_pha('core', 'src.pi') read ARF file src.arf read RMF file src.rmf read background file src_bkg.pi >>> (chans,) = get_indep() >>> (elo, ehi) = get_axes() >>> chans[0:5] array([ 1., 2., 3., 4., 5.]) >>> elo[0:5] array([ 0.0073, 0.0146, 0.0292, 0.0438, 0.0584]) >>> ehi[0:5] array([ 0.0146, 0.0292, 0.0438, 0.0584, 0.073 ])

The image has 101 columns by 108 rows. The `get_indep`

function returns one-dimensional arrays, for the full dataset, whereas `get_axes` returns values for the individual axis:

>>> load_image('img', 'img.fits') >>> get_data('img').shape (108, 101) >>> set_coord('img', 'physical') >>> (x0, x1) = get_indep('img') >>> (a0, a1) = get_axes('img') >>> (x0.size, x1.size) (10908, 10908) >>> (a0.size, a1.size) (101, 108) >>> np.all(x0[:101] == a0) True >>> np.all(x1[::101] == a1) True

PARAMETERS

The parameters for this function are:

Parameter
Definition
id
The identifier for the data set to use. If not given then the default identifier is used, as returned by

`get_default_id` .
bkg_id
Set if the values returned should be from the given background component, instead of the source data set.

The return value from this function is:

axis -- The independent axis values. The differences to `get_dep`

that this represents the "alternate grid" for the axis. For PHA data, this is the energy grid (E_MIN and E_MAX). For image data it is an array for each axis, of the length of the axis, using the current coordinate system for the data set.

See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

December 2023