Zero spacings are computed when the single dish diameter is the
same as the interferometer dish diameter. Zero spacing extraction pro-
ceeds differently for Class data tables and 3-D data cubes.
In the data cube case, the nearest pixel matching the direction of each
field is taken as the Zero spacing for this field. If there is no point
close enough, according to the specified position tolerance SHORT_TOLE,
an error occurs.
In the Class data table case, all spectra within the specified position
tolerance of a field center are averaged together to produce the Zero
spacing. If none is found, an error occcurs.
Gildas manager
2023-06-01