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2.3.4.4 The uvrange Parameter

Rows in the MS can also be selected based on the uv-distance or physical baseline length that the visibilities in each row correspond to. This uvrange can be specified in various formats.

The basic building block of uv-distance specification is a valid number with optional units in the format N[UNIT] (the unit in square brackets is optional). We refer to this basic building block as UVDIST. The default unit is meter. Units of length (such as ’m’ and ’km’) select physical baseline distances (independent of wavelength). The other allowed units are in wavelengths (such as ’lambda’, ’klambda’ and ’Mlambda’ and are true uv-plane radii

      ∘ -------
ruv =   u2 + v2.
(2.1)

If only a single UVDIST is specified, all rows, the uv-distance of which exactly matches the given UVDIST, are selected.

UVDIST can be specified as a range in the format ’N0~N1[UNIT]’ (where N0 and N1 are valid numbers). All rows corresponding to uv-distance between N0 and N1 (inclusive) when converted the specified units are selected.

UVDIST can also be selected via comparison operators. When specified in the format ’>UVDIST’, all visibilities with uv-distances greater than the given UVDIST are selected. Likewise, when specified in the format ’<UVDIST’, all rows with uv-distances less than the given UVDIST are selected.

Any number of above mentioned uv-distance specifications can be given as a comma-separated list.

Examples:

  uvrange = ’100~200km’                     # an annulus in physical baseline length  
  uvrange = ’24~35Mlambda, 40~45Mlambda’    # two annuli in units of mega-wavelengths  
  uvrange = ’< 45klambda’                   # less than 45 kilolambda  
  uvrange = ’> 0lambda’                     # greater than zero length (no auto-corrs)  
  uvrange = ’100km’                         # baselines of length 100km  
  uvrange = ’100klambda’                    # uv-radius 100 kilolambda


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