# Principle

The new implementation of the UV_MAP command uses most of the older code, but re-arranged such that ensembles of contiguous channels (“chunks”) are treated at once and share the same synthesized beam. Deconvolution with CLEAN then proceeds by using the synthesized beam with the appropriate frequency for each channel. The user can control the “chunk” size, and hence the precision of the process given the desired field of view.

From the user point of view, Mosaics are now treated as the Single field case. The same commands UV_MAP and CLEAN automatically recognize whether there is one or more fields to be treated. For the user, the imaging sequence is thus always the same

    READ UV MyData.uvt /RANGE Min Max Type
    ! here, optionally use UV_TIME, UV_COMPRESS, UV_BASELINE
    ! or UV_FILTER, UV_CONT to filter lines or remove continuum
    UV_MAP  ! Image
    CLEAN   ! Deconvolve
    ! here, optionally use UV_RESTORE
    WRITE * MyData  ! Save result if OK

The only difference between the single field and mosaic cases is that MAPPING yields a Sky brightness image for Mosaics, but does not automatically correct for primary beam attenuation for Single fields.

As a result of the new concept, beams (whether primary or synthesized) can be 4-D arrays, as they may depend on Frequency and Field.

Imaging parameters are controlled by the MAP_* variables. Suitable defaults are provided, and variations can be suggested by command UV_STAT. It is anticipated the Deconvolution parameters would be controlled by CLEAN_* variables.

Subsections

- Multi-Fields UV table
  - Importing from UVFITS
  - Importing from CLIC
  - Importing from separate fields.
- Multi-Field UV_MAP processing
- Multi-Field CLEANing
- Short Spacings