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Some comments on capabilities available inside AIPS++

Tables

All data, original and calibration, is placed in the Table system, where it is accessible and modifiable by a number of ``free-form'' mechanisms, the principle being glish and the tablebrowser.

The MeasurementSet

is of the form one main Table, plus many subsiduary Tables (e.g. ANTENNA, FEED, ARRAY). The main table contains data, coordinate information such as time and uvw, and keys into the sub-Tables (see Wieringa and Cornwell, 1996).

keys

ANTENNA1, ANTENNA2, ARRAY_ID, CORRELATOR_ID, FEED1, FEED2, FIELD_ID, OBSERVATION_ID, PULSAR_ID, SOURCE_ID, SPECTRAL_WINDOW_ID

coordinates

SCAN_NUMBER, UVW, TIME, EXPOSURE, INTERVAL, PULSAR_BIN

data

DATA, SIGMA, WEIGHT, WEIGHT_SPECTRUM, FLAG, FLAG_ROW

Selection

of data from a MS leads to another reference MS with little overhead. The selection can be by one or more of:

• data (e.g. ``all amplitudes $\geq$ 5 Jy''),
• coordinates (e.g. ``all times in the following range''),
• keys (e.g. ``SPECTRAL_WINDOW_ID=1 or 4''),
• properties determined by lookup in a subtable (e.g. ``wind velocity $\leq$ 3 m/s''),

The MeasurementEquation

is the fundamental mechanism used to describe calibration and imaging in terms of MeasurementComponents. These describe some aspect of the measurement process, such as antenna-based gain, while not prescribing how the calculation of actual values is to be performed, for instance in the case of antenna phases via a table calculated from a priori values or via a phase-screen model.