Changeset 1854


Ignore:
Timestamp:
08/04/10 18:28:06 (14 years ago)
Author:
Malte Marquarding
Message:

Ticket #194: Added more description of the scantable

File:
1 edited

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  • trunk/doc/source/developer/scantable.rst

    r1852 r1854  
    99based on the data abstraction of the PKSreader API.
    1010
     11ASAP data handling works on objects called scantables. A scantable holds your
     12data, and also provides functions to operate upon it.
     13
     14The building block of a scantable is an integration, which is a single row of
     15a scantable. Each row contains just one spectrum for each beam, IF and
     16polarisation. For example Parkes OH-multibeam data would normally contain
     1713 beams, 1 IF and 2 polarisations, Parkes methanol-multibeam data would
     18contain 7 beams, 2 IFs and 2 polarisations while the Mopra 8-GHz MOPS
     19filterbank will produce one beam, many IFs, and 2-4 polarisations.
     20
     21All of the combinations of Beams/IFs an Polarisations are contained in separate
     22rows. These rows are grouped in cycles (same time stamp).
     23
     24A collection of cycles for one source is termed a scan (and each scan has a
     25unique numeric identifier, the SCANNO). A scantable is then a collection of
     26one or more scans. If you have scan-averaged your data in time, i.e. you
     27have averaged all cycles within a scan, then each scan would hold just
     28one (averaged) integration.
     29
    1130Schema
    1231======
    1332
    1433The Scantable consist of a main (casacore) Table and several sub-tables which
    15 are referenced via _id_.
     34are referenced via **ID**. The following descriptions use the following syntax
     35
     36    **COLUMN/KEYWORD NAME** - *DATA_TYPE(N)=DEFAULT_VALUE*
     37
     38where *DEFAULT_VALUE* is optional and *(N)* indicates a Vector of that type
    1639
    1740----------
     
    2043
    2144The main table consists of global data (keywords) and row-based data (columns)
     45
     46
     47Keywords
     48--------
     49
     50* **VERSION** - *uInt*
     51
     52    the version of the scantable for compatibility tests
     53
     54* **POLTYPE** - *String=linear*
     55
     56    the polarisation type, i.e. *stokes*, *linear* or *circular*
     57
     58* **DIRECTIONREF** - *String=J2000*
     59
     60    the reference frame of the direction (coordinate) [redundant?!]
     61
     62* **OBSMODE** - *String=""*
     63
     64    no idea...
     65
     66* **UTC** - *String*
     67
     68    most likely the starting time of the observation (file)
     69
     70* **AntennaName** - *String*
     71
     72    the name of the antenna
     73
     74* **AntennaPosition** - *Double(3)*
     75
     76    the WGS position of the antenna
     77
     78* **FluxUnit** - *String*
     79
     80    the unit of the channel values i.e. *Jy* or *K*
     81
     82* **Observer** - *String*
     83
     84    the name of the observer
     85
     86* **Obstype** -  *String*
     87
     88    probably telescope specific name/encoding
     89
     90* **Project** -  *String*
     91
     92    e.g. proposal project number, survey name
     93
     94* **Bandwidth** - *Double*
     95
     96    self-explanatory
     97
     98* **nIF, nBeam, nPol, nChan** - *Int*
     99
     100    the number of IF, Beam, Polarisation and Channel values in the scantable
     101    This is currently **FIXED**
     102
     103* **FreqRefFrame** - *String*
     104
     105    redundant info - also in **FREQUENCIES** sub-table
     106
     107* **FreqRefVal** - *Double*
     108
     109    no idea...
    22110
    23111Columns
     
    36124    the channel-based system temperature values
    37125
    38 * **FLAGROW** - *uInt*
     126* **FLAGROW** - *uInt=-1*
    39127
    40128    spectrum based flags
     
    60148    the name of the source observered
    61149
    62 * **SRCTYPE** - *Int*
     150* **SRCTYPE** - *Int=-1*
    63151
    64152    the tyep of the source, i.e. indicating if it is an on source scan or
     
    81169             Imag(XY)=3
    82170
    83 * **REFBEAMNO** - *Int*
     171* **REFBEAMNO** - *Int=-1*
    84172
    85173    optional index of the reference beam in a multibeam obervation
    86174
    87 * **FREQ_ID, MOLECULE_ID, TCAL_ID, FOCUS_ID, WEATHER_ID, FIT_ID**
    88 
     175* **FREQ_ID, MOLECULE_ID, TCAL_ID, FOCUS_ID, WEATHER_ID, FIT_ID** - *Int*
     176
     177    the reference indeces to the sub-tables
     178
     179* **FIELDNAME** - *string*
     180
     181    the name of the field the source belongs to
     182
     183* **OPACITY** - *Float*
     184
     185    maybe redundant - not used anywhere
     186
     187* **SRCPROPERMOTION, SRCVELOCITY, SRCDIRECTION**
     188
     189    see livedata docs - not used in ASAP
     190
     191* **SCANRATE**
     192
     193    see livedata docs - not used in ASAP
    89194
    90195----------
     
    95200---------
    96201
    97 blah blah
     202""""""""
     203Keywords
     204""""""""
     205
     206* **BASEFRAME** - *String=TOPO*
     207* **FRAME** - *String=TOPO*
     208* **EQUINOX** - *String=J2000*
     209* **UNIT** - *String=""*
     210* **DOPPLER** - *String=RADIO*
     211
     212"""""""
     213Columns
     214"""""""
     215
     216* **REFPIX** - *Double*
     217
     218* **REFVAL** - *Double*
     219
     220* **INCREMENT** - *Double*
     221
     222MOLECULES
     223---------
     224
     225""""""""
     226Keywords
     227""""""""
     228
     229* **UNIT** - *String=Hz*
     230
     231"""""""
     232Columns
     233"""""""
     234
     235* **RESTFREQUENCY** - *Double()*
     236* **NAME** - *String()*
     237* **FORMATTEDNAME** - *String()*
    98238
    99239
     
    104244MS
    105245==
     246
     247MeasurementSets are specifically designed for synthesis data. As such one of the
     248main dfferences between the Scantable and a MS is how spectra are stored.
     249An MS usually stores those in an n_pol x n_channel complex matrix whereas the
     250Scantable stores each polarisation seperately. In case of polarimetry data the
     251(complex) cross-polarisation is serialised into real and imaginary parts, e.g. a
     252total of four rows would descibe one polarisation.
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