Last modified: December 2023

AHELP for CIAO 4.16 Sherpa


Context: data


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.


Example 1

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])

Example 2

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 ])

Example 3

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)
>>> np.all(x1[::101] == a1)


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.

Return value

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.

See Also

get_conf, get_conf_results, get_covar, get_covar_opt, get_covar_results, get_covariance_results, get_int_proj, get_int_unc, get_proj, get_proj_opt, get_proj_results, get_projection_results, get_reg_proj, get_reg_unc
get_chart_spectrum, get_marx_spectrum
copy_data, dataspace1d, dataspace2d, datastack, delete_data, fake, get_areascal, get_arf, get_arf_plot, get_backscal, get_bkg, get_bkg_arf, get_bkg_chisqr_plot, get_bkg_delchi_plot, get_bkg_fit_plot, get_bkg_model, get_bkg_model_plot, get_bkg_plot, get_bkg_ratio_plot, get_bkg_resid_plot, get_bkg_rmf, get_bkg_scale, get_bkg_source, get_bkg_source_plot, get_coord, get_counts, get_data, get_data_contour, get_data_contour_prefs, get_data_image, get_data_plot, get_data_plot_prefs, get_dep, get_dims, get_error, get_exposure, get_grouping, get_indep, get_quality, get_rmf, get_specresp, get_staterror, get_syserror, group, group_adapt, group_adapt_snr, group_bins, group_counts, group_snr, group_width, load_ascii, load_data, load_grouping, load_quality, set_data, set_quality, ungroup, unpack_ascii, unpack_data
get_filter, load_filter, set_filter
calc_stat_info, get_stat_info
get_default_id, list_data_ids, list_response_ids, list_stats
get_draws, get_iter_method_name, get_iter_method_opt, get_method, get_method_name, get_method_opt
clean, get_model, get_model_component, get_model_component_image, get_model_component_plot, get_model_plot, get_num_par, get_num_par_frozen, get_num_par_thawed, get_order_plot, get_par, get_pileup_model, get_response, get_source, get_source_component_image, get_source_component_plot, get_source_contour, get_source_image, get_source_plot, image_source
get_split_plot, plot_data, set_xlinear, set_xlog, set_ylinear, set_ylog
get_psf, get_psf_contour, get_psf_image, get_psf_plot
save_error, save_filter, save_grouping, save_quality, save_staterror, save_syserror
get_chisqr_plot, get_delchi_plot, get_prior, get_sampler, get_stat, get_stat_name
calc_data_sum, calc_data_sum2d, calc_ftest, calc_kcorr, calc_mlr, calc_model_sum2d, calc_source_sum2d, get_analysis, get_rate
contour, contour_data, contour_ratio, histogram1d, histogram2d, image_data, image_getregion, rebin