Keywords: imager

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## UV Table handling

Besides the magenta`READ UV` and magenta`WRITE UV` commands to read or write uv tables, [rgb]1,0,0IMAGER has a number of commands to manipulate the current uv table buffer. These commands have names starting by magenta`UV_`. Most of them are in the blue`CLEAN\` language, some in the blue`ADVANCED\` one.

[rgb]1,0,0IMAGER works using UV buffers. Most commands only work on the current UV buffer, but some of them keep track of the previous buffer to allow the user to revert the operation.

Data inspection and editing:
  - magenta`SHOW COVERAGE` display the uv coverage
  - magenta`SHOW UV` display the uv data
  - magenta`UV_FLAG` allow flagging visibilities
  - magenta`UV_PREVIEW` provides a quick view of the visibilities as a function of frequencies, and attempts to automatically find the continuum level and parts of the bandwidth with spectral line emissions.

Data size reduction routines:
  - magenta`UV_COMPRESS` is a simple spectral smoothing, providing only channel averaging by integer number of channels.
  - magenta`UV_RESAMPLE` provides a more flexible spectral smoothing and resampling facility.
  - magenta`UV_TIME` can be used to time-average the UV data set, leading to faster processing. However, using magenta`UV_TIME` too early may limit your ability to perform accurate phase self-calibration.

Continuum processing commands:
  - magenta`UV_BASELINE` allows to remove the continuum baseline, by 0th or 1st order baseline fitting of each visibility.
  - Conversely, magenta`UV_FILTER` will filter the spectral line range to leave only the channels with continuum emission. Both magenta`UV_BASELINE` and magenta`UV_FILTER` can use the results provided by magenta`UV_PREVIEW` to specify where spectral lines may be found.
  - magenta`UV_CONTINUUM` converts a spectral line uv table into a bandwidth synthesis continuum uv table. magenta`UV_CONTINUUM` is only useful for UV plane analysis: see Section for details.
  - magenta`UV_MERGE /FILE` can merge several UV continuum tables with a specified spectral index to optimize the sensitivity.

Image preparation:
  - magenta`UV_CHECK` inspects the uv data to figure out how many different synthesized beams are needed.
  - magenta`UV_SHORT` adds the short (or zero) spacing information provided by an additional single dish data, read by magenta`READ SINGLE`.
  - magenta`UV_STAT` evaluates the impact of robust weighting and tapering on the synthesized beam. It provides recommendations for the image and pixel sizes.
  - magenta`UV_TRUNCATE` restricts the uv baseline length range.

UV Plane analysis:
  - magenta`UV_FIT` fit simple source models to the visbilities.
  - magenta`SHOW UV_FIT` display the fit results, usually as a function of frequency, but also in other ways.

Miscellaneous:
  - magenta`UV_DEPROJECT` de-projects the coordinates given a specified phase center, orientation and inclination. This can be useful for inclined, flattened, nearly axi-symmetric structures such as proto-planetary disks or galaxies.
  - magenta`UV_CIRCLE` and magenta`UV_RADIAL` compute the azimutal average of the visibilities. They are useful for rotationally symmetric structures such as proto-planetary disks or circumstellar envelopes, for example.
  - magenta`UV_REWEIGHT` changes the visibility weights.
  - magenta`UV_SHIFT` changes the phase center. This can be useful for UV plane analysis.
  - magenta`UV_MERGE /FILE` can merge several UV tables, Line or Continuum. It also allows stacking different spectral lines, by aligning them in velocity, as well as stacking emission from different sources.

The remaining magenta`UV_...` commands are related to imaging and deconvolution: magenta`UV_MAP` computes the dirty image, magenta`UV_RESTORE` computes the Clean image from a Clean component list by removal of the Clean components in the uv plane, and imaging of the residuals. magenta`UV_RESIDUAL` just computes the residuals by subtraction of the Clean components.

Finally, magenta`UV_SELF`, in the blue`CALIBRATE\` language, is a specific variant of magenta`UV_MAP` used to compute the intermediate images required for self-calibration. It is not intended for direct use by normal users.

Next: Single-field imaging and deconvolution Up: The input data: UV Previous: Reading UV tables Contents Index