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UV Tables are now a very special subset of GILDAS data files. As any
GILDAS data file, they are identified by an integer code stored in
variable h%gil%type_gdf (see Table 2) which,
for UV Tables must take the value code_gdf_uvt or
code_gdf_tuv, depending whether the table is in native
order (a visibility being contiguous in memory) or transposed. For
simplicity, we have imposed code_gdf_tuv = -code_gdf_uvt.
The new layout differ in several ways from the older one. In short:
- the daps are no longer at pre-defined positions in
the data file, but their positions are described by the UV table
header.
- the complex visibility elements are not necessarily
(real, imaginary, weight) triplets, but contain
h%gil%natom elements. For example, a zero spacing UV
table from a single-dish spectrum may have h%gil%natom =
2 (as the imaginary part is 0 in such a case).
- Provision is made to handle polarization data, by indicating
the number of Stokes parameters in a visibility,
h%gil%nstokes.
- The number of frequency channels
h%gil%nchan and the number of visibilities
h%gil%nvisi are available independently of the
transposition status of the UV data set.
The UV specific information is included in the uvda section
of the h%gil header, as described in
appendix B.
Next: Dap positions and Size
Up: The new layout
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Gildas manager
2014-07-01