20.22.5 Zero_Spacing

Zero spacings are computed when the single dish diameter is the same as the interferometer dish diameter. Zero spacing extraction proceeds 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.