Basic Structure

ASAP data handling works on objects called scantables. A scantable holds your data, and also provides functions to operate upon it.

The building block of a scantable is an integration, which is a single row of a scantable. Each row contains just one spectrum for each beam, IF and polarisation. For example Parkes OH-multibeam data would normally contain 13 beams, 1 IF and 2 polarisations, Parkes methanol-multibeam data would contain 7 beams, 2 IFs and 2 polarisations while the Mopra 8-GHz MOPS filterbank will produce one beam, many IFs, and 2-4 polarisations.

All of the combinations of Beams/IFs an Polarisations are contained in separate rows. These rows are grouped in cycles (same time stamp).

A collection of cycles for one source is termed a scan (and each scan has a unique numeric identifier, the SCANNO). A scantable is then a collection of one or more scans. If you have scan-averaged your data in time, i.e. you have averaged all cycles within a scan, then each scan would hold just one (averaged) integration.

Many of the functions which work on scantables can either return a new scantable with modified data or change the scantable insitu. Which method is used depends on the users preference. The default can be changed via the .asaprc resource file.

For example a Mopra scan with a 4s integration time, two IFs and dual polarisations has two (2s) cycles.

    SCANNO  CYCLENO BEAMNO IFNO POLNO
    0       0       0      0    0
    0       0       0      0    1
    0       0       0      1    0
    0       0       0      1    1
    0       1       0      0    0
    0       1       0      0    1
    0       1       0      1    0
    0       1       0      1    1