ngcasa.imaging.make_imaging_weight

make_imaging_weight(vis_mxds, imaging_weights_parms, grid_parms, sel_parms)[source]

Creates the imaging weight data variable that has dimensions time x baseline x chan x pol (matches the visibility data variable). The weight density can be averaged over channels or calculated independently for each channel using imaging_weights_parms[‘chan_mode’]. The following imaging weighting schemes are supported ‘natural’, ‘uniform’, ‘briggs’, ‘briggs_abs’. The grid_parms[‘image_size’] and grid_parms[‘cell_size’] should usually be the same values that will be used for subsequent synthesis blocks (for example making the psf). To achieve something similar to ‘superuniform’ weighting in CASA tclean grid_parms[‘image_size’] and imaging_weights_parms[‘cell_size’] can be varied relative to the values used in subsequent synthesis blocks.

Parameters

  • vis_mxds (xarray.core.dataset.Dataset) – Input multi-xarray Dataset with global data.

  • imaging_weights_parms (dictionary) –

  • imaging_weights_parms['weighting'] ({'natural', 'uniform', 'briggs', 'briggs_abs'}, default = natural) – Weighting scheme used for creating the imaging weights.

  • imaging_weights_parms['robust'] (number, acceptable range [-2,2], default = 0.5) – Robustness parameter for Briggs weighting. robust = -2.0 maps to uniform weighting. robust = +2.0 maps to natural weighting.

  • imaging_weights_parms['briggs_abs_noise'] (number, default=1.0) – Noise parameter for imaging_weights_parms[‘weighting’]=’briggs_abs’ mode weighting.

  • grid_parms (dictionary) –

  • grid_parms['image_size'] (list of int, length = 2) – The image size (no padding).

  • grid_parms['cell_size'] (list of number, length = 2, units = arcseconds) – The image cell size.

  • grid_parms['chan_mode'] ({'continuum'/'cube'}, default = 'continuum') – Create a continuum or cube image.

  • grid_parms['fft_padding'] (number, acceptable range [1,100], default = 1.2) – The factor that determines how much the gridded visibilities are padded before the fft is done.

  • sel_parms (dictionary) –

  • sel_parms['xds'] (str) – The xds within the mxds to use to calculate the imaging weights for.

  • sel_parms['data_group_in_id'] (int, default = first id in xds.data_groups) – The data group in the xds to use.

  • sel_parms['data_group_out_id'] (int, default = sel_parms['data_group_id']) – The output data group. The default will append the imaging weight to the input data group.

  • sel_parms['imaging_weight'] (str, default ='IMAGING_WEIGHT') – The name of that will be used for the imaging weight data variable.

Returns

vis_xds – The vis_xds will contain a new data variable for the imaging weights the name is defined by the input parameter sel_parms[‘imaging_weight’].

Return type

xarray.core.dataset.Dataset