Keywords: sic-gdfv2

Next: Dap positions and size Up: The new layout Previous: The new layout Contents

### Data Format Identification

UV Tables are now a special subset of GDF files. As any GDF 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 differs 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 (cf. the following section for details).
- 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 Previous: The new layout Contents