State Information

NRAO Home > CASA > CASA Cookbook and User Reference Manual

8.3.3.2 State Information

Some properties of a scantable apply to all of the data, such as spectral units, frequency frame, or Doppler type. This information can be set using the scantable.set_xxxx methods. These are currently:

CASA <1>: sd.scantable.set_<TAB>
sd.scantable.set_dirframe    sd.scantable.set_restfreqs
sd.scantable.set_doppler     sd.scantable.set_selection
sd.scantable.set_feedtype    sd.scantable.set_sourcetype
sd.scantable.set_fluxunit    sd.scantable.set_spectrum
sd.scantable.set_freqframe   sd.scantable.set_unit
sd.scantable.set_instrument

For example, sd.scantable.set_fluxunit sets the default units that describe the flux axis:

scans.set_fluxunit(’K’) # Set the flux unit for data to Kelvin

Choices are ’K’ or ’Jy’. Note: the scantable.set_fluxunit function only changes the name of the current fluxunit. To change fluxunits, use scantable.convert_flux as described in § 8.3.4.2 instead (currently it is necessary to do some gymnastics for non-AT telescopes).

Use sd.scantable.set_unit to set the units to be used on the spectral axis:

scans.set_unit(’GHz’) # Use GHz as the spectral axis for plots

The choices for the units are ’km/s’, ’channel’, or ’*Hz’ (e.g. ’GHz’, ’MHz’, ’kHz’, ’Hz’). This does the proper conversion using the current frame and Doppler reference as can be seen when the spectrum is plotted.

Set the frame in which the frequency (spectral) axis is defined by sd.scantable.set_freqframe:

CASA <2>: help(sd.scantable.set_freqframe)
Help on method set_freqframe in module asap.scantable:

set_freqframe(self, frame=None) unbound asap.scantable.scantable method
    Set the frame type of the Spectral Axis.
    Parameters:
        frame:   an optional frame type, default ’LSRK’. Valid frames are:
                 ’REST’, ’TOPO’, ’LSRD’, ’LSRK’, ’BARY’,
                 ’GEO’, ’GALACTO’, ’LGROUP’, ’CMB’
    Examples:
        scan.set_freqframe(’BARY’)

The most useful choices here are frame = ’LSRK’ (the default for the function) and frame = ’TOPO’ (what the GBT actually observes in). Note that the ’REST’ option is not yet available. The Doppler frame is set with sd.scantable.set_doppler:

CASA <3>: help(sd.scantable.set_doppler)
Help on method set_doppler in module asap.scantable:

set_doppler(self, doppler=’RADIO’) unbound asap.scantable.scantable method
    Set the doppler for all following operations on this scantable.
    Parameters:
        doppler:    One of ’RADIO’, ’OPTICAL’, ’Z’, ’BETA’, ’GAMMA’

Finally, there are a number of functions to query the state of the scantable. These can be found in the usual way:

CASA <4>: sd.scantable.get<TAB>
sd.scantable.get_abcissa       sd.scantable.get_parangle
sd.scantable.get_antennaname   sd.scantable.get_restfreqs
sd.scantable.get_azimuth       sd.scantable.get_rms
sd.scantable.get_column_names  sd.scantable.get_row
sd.scantable.get_coordinate    sd.scantable.get_row_selector
sd.scantable.get_direction     sd.scantable.get_scan
sd.scantable.get_directionval  sd.scantable.get_selection
sd.scantable.get_elevation     sd.scantable.get_sourcename
sd.scantable.get_fit           sd.scantable.get_spectrum
sd.scantable.get_fluxunit      sd.scantable.get_time
sd.scantable.get_inttime       sd.scantable.get_tsys
sd.scantable.get_mask          sd.scantable.get_tsysspectrum
sd.scantable.get_mask_indices  sd.scantable.get_unit
sd.scantable.get_masklist      sd.scantable.get_weather

These include functions to get the current values of the states mentioned above, as well as methods to query the number of scans, IFs, and polarizations in the scantable and their designations. See the inline help of the individual functions for more information.

[next] [prev] [prev-tail] [front] [up]

More information about CASA may be found at the CASA web page

This code is available under the terms of the GNU General Public Lincense