[1852] | 1 | ===================== |
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| 2 | Scantable Description |
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| 3 | ===================== |
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| 4 | |
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| 5 | Introduction |
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| 6 | ============ |
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| 7 | |
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| 8 | The Scantable is the ASAP single-dish data container. It was designed |
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| 9 | based on the data abstraction of the PKSreader API. |
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| 10 | |
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[1854] | 11 | ASAP data handling works on objects called scantables. A scantable holds your |
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| 12 | data, and also provides functions to operate upon it. |
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| 13 | |
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| 14 | The building block of a scantable is an integration, which is a single row of |
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| 15 | a scantable. Each row contains just one spectrum for each beam, IF and |
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| 16 | polarisation. For example Parkes OH-multibeam data would normally contain |
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| 17 | 13 beams, 1 IF and 2 polarisations, Parkes methanol-multibeam data would |
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| 18 | contain 7 beams, 2 IFs and 2 polarisations while the Mopra 8-GHz MOPS |
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| 19 | filterbank will produce one beam, many IFs, and 2-4 polarisations. |
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| 20 | |
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| 21 | All of the combinations of Beams/IFs an Polarisations are contained in separate |
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| 22 | rows. These rows are grouped in cycles (same time stamp). |
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| 23 | |
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| 24 | A collection of cycles for one source is termed a scan (and each scan has a |
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| 25 | unique numeric identifier, the SCANNO). A scantable is then a collection of |
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| 26 | one or more scans. If you have scan-averaged your data in time, i.e. you |
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| 27 | have averaged all cycles within a scan, then each scan would hold just |
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| 28 | one (averaged) integration. |
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| 29 | |
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[1852] | 30 | Schema |
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| 31 | ====== |
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| 32 | |
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| 33 | The Scantable consist of a main (casacore) Table and several sub-tables which |
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[1854] | 34 | are referenced via **ID**. The following descriptions use the following syntax |
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[1852] | 35 | |
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[1854] | 36 | **COLUMN/KEYWORD NAME** - *DATA_TYPE(N)=DEFAULT_VALUE* |
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| 37 | |
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| 38 | where *DEFAULT_VALUE* is optional and *(N)* indicates a Vector of that type |
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| 39 | |
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[1852] | 40 | ---------- |
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| 41 | Main Table |
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| 42 | ---------- |
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| 43 | |
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| 44 | The main table consists of global data (keywords) and row-based data (columns) |
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| 45 | |
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[1854] | 46 | |
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| 47 | Keywords |
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| 48 | -------- |
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| 49 | |
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| 50 | * **VERSION** - *uInt* |
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| 51 | |
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| 52 | the version of the scantable for compatibility tests |
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| 53 | |
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| 54 | * **POLTYPE** - *String=linear* |
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| 55 | |
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| 56 | the polarisation type, i.e. *stokes*, *linear* or *circular* |
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| 57 | |
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| 58 | * **DIRECTIONREF** - *String=J2000* |
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| 59 | |
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| 60 | the reference frame of the direction (coordinate) [redundant?!] |
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| 61 | |
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| 62 | * **OBSMODE** - *String=""* |
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| 63 | |
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| 64 | no idea... |
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| 65 | |
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| 66 | * **UTC** - *String* |
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| 67 | |
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| 68 | most likely the starting time of the observation (file) |
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| 69 | |
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| 70 | * **AntennaName** - *String* |
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| 71 | |
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| 72 | the name of the antenna |
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| 73 | |
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| 74 | * **AntennaPosition** - *Double(3)* |
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| 75 | |
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| 76 | the WGS position of the antenna |
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| 77 | |
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| 78 | * **FluxUnit** - *String* |
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| 79 | |
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| 80 | the unit of the channel values i.e. *Jy* or *K* |
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| 81 | |
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| 82 | * **Observer** - *String* |
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| 83 | |
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| 84 | the name of the observer |
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| 85 | |
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| 86 | * **Obstype** - *String* |
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| 87 | |
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| 88 | probably telescope specific name/encoding |
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| 89 | |
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| 90 | * **Project** - *String* |
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| 91 | |
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| 92 | e.g. proposal project number, survey name |
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| 93 | |
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| 94 | * **Bandwidth** - *Double* |
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| 95 | |
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| 96 | self-explanatory |
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| 97 | |
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| 98 | * **nIF, nBeam, nPol, nChan** - *Int* |
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| 99 | |
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| 100 | the number of IF, Beam, Polarisation and Channel values in the scantable |
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| 101 | This is currently **FIXED** |
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| 102 | |
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| 103 | * **FreqRefFrame** - *String* |
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| 104 | |
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| 105 | redundant info - also in **FREQUENCIES** sub-table |
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| 106 | |
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| 107 | * **FreqRefVal** - *Double* |
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| 108 | |
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| 109 | no idea... |
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| 110 | |
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[1852] | 111 | Columns |
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| 112 | ------- |
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| 113 | |
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| 114 | * **SPECTRA** - *Float(nchannel)* |
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| 115 | |
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| 116 | the spectral channel data. |
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| 117 | |
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| 118 | * **FLAGTRA** - *uChar(nchannel)* |
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| 119 | |
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| 120 | the corresponding flags |
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| 121 | |
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| 122 | * **TSYS** - *Float(nchannel)* |
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| 123 | |
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| 124 | the channel-based system temperature values |
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| 125 | |
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[1854] | 126 | * **FLAGROW** - *uInt=-1* |
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[1852] | 127 | |
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| 128 | spectrum based flags |
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| 129 | |
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| 130 | * **TIME** - *MEpoch* |
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| 131 | |
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| 132 | The mjd time when the observation took place |
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| 133 | |
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| 134 | * **INTERVAL** - *Double* |
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| 135 | |
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| 136 | the integration time in seconds |
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| 137 | |
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| 138 | * **DIRECTION** - *MDirection* |
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| 139 | |
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| 140 | the associated direction on the sky |
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| 141 | |
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| 142 | * **AZIMUTH, ELEVATION** - *Float* |
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| 143 | |
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| 144 | the azimuth/elevation when the spectrum was collected |
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| 145 | |
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| 146 | * **SRCNAME** - *string* |
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| 147 | |
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| 148 | the name of the source observered |
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| 149 | |
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[1854] | 150 | * **SRCTYPE** - *Int=-1* |
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[1852] | 151 | |
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| 152 | the tyep of the source, i.e. indicating if it is an on source scan or |
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| 153 | off source. This will be used for calibration |
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| 154 | |
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| 155 | * **SCANNO, BEAMNO, POLNO, IFNO, CYCLENO** - *uInt* |
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| 156 | |
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| 157 | These columns index (0-based) the respective values. |
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| 158 | |
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| 159 | * SCANNO: the number odf the scan. A scan is usually multiple integrations |
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| 160 | (cycles) |
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| 161 | |
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| 162 | * CYCLENO: the integration number within a scan (sub-scan?) |
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| 163 | |
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| 164 | * IFNO: the index of the IF (spectral window) |
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| 165 | |
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| 166 | * BEAMNO: the index of the beam (in a multibeam system) |
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| 167 | |
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| 168 | * POLNO: the index of the polarisation, e.g. XX=0, YY=1, Real(XY)=2, |
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| 169 | Imag(XY)=3 |
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| 170 | |
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[1854] | 171 | * **REFBEAMNO** - *Int=-1* |
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[1852] | 172 | |
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| 173 | optional index of the reference beam in a multibeam obervation |
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| 174 | |
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[1854] | 175 | * **FREQ_ID, MOLECULE_ID, TCAL_ID, FOCUS_ID, WEATHER_ID, FIT_ID** - *Int* |
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[1852] | 176 | |
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[1854] | 177 | the reference indeces to the sub-tables |
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[1852] | 178 | |
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[1854] | 179 | * **FIELDNAME** - *string* |
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| 180 | |
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| 181 | the name of the field the source belongs to |
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| 182 | |
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| 183 | * **OPACITY** - *Float* |
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| 184 | |
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| 185 | maybe redundant - not used anywhere |
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| 186 | |
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| 187 | * **SRCPROPERMOTION, SRCVELOCITY, SRCDIRECTION** |
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| 188 | |
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| 189 | see livedata docs - not used in ASAP |
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| 190 | |
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| 191 | * **SCANRATE** |
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| 192 | |
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| 193 | see livedata docs - not used in ASAP |
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| 194 | |
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[1852] | 195 | ---------- |
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| 196 | Sub-Tables |
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| 197 | ---------- |
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| 198 | |
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| 199 | FREQUENCY |
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| 200 | --------- |
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| 201 | |
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[1854] | 202 | """""""" |
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| 203 | Keywords |
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| 204 | """""""" |
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[1852] | 205 | |
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[1854] | 206 | * **BASEFRAME** - *String=TOPO* |
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| 207 | * **FRAME** - *String=TOPO* |
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| 208 | * **EQUINOX** - *String=J2000* |
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| 209 | * **UNIT** - *String=""* |
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| 210 | * **DOPPLER** - *String=RADIO* |
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[1852] | 211 | |
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[1854] | 212 | """"""" |
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| 213 | Columns |
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| 214 | """"""" |
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| 215 | |
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| 216 | * **REFPIX** - *Double* |
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| 217 | |
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| 218 | * **REFVAL** - *Double* |
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| 219 | |
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| 220 | * **INCREMENT** - *Double* |
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| 221 | |
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| 222 | MOLECULES |
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| 223 | --------- |
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| 224 | |
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| 225 | """""""" |
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| 226 | Keywords |
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| 227 | """""""" |
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| 228 | |
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| 229 | * **UNIT** - *String=Hz* |
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| 230 | |
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| 231 | """"""" |
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| 232 | Columns |
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| 233 | """"""" |
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| 234 | |
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| 235 | * **RESTFREQUENCY** - *Double()* |
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| 236 | * **NAME** - *String()* |
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| 237 | * **FORMATTEDNAME** - *String()* |
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| 238 | |
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[1871] | 239 | FOCUS |
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| 240 | ----- |
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| 241 | |
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| 242 | """""""" |
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| 243 | Keywords |
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| 244 | """""""" |
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| 245 | |
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| 246 | * **PARALLACTIFY** - *Bool=False* |
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| 247 | |
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| 248 | indicates whether the observation was parallactified i.e. observed in such |
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| 249 | a way that the sum of the phases is zero. |
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| 250 | |
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| 251 | """"""" |
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| 252 | Columns |
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| 253 | """"""" |
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| 254 | |
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| 255 | * **PARANGLE** - *Float* |
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| 256 | |
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| 257 | the parallacticle angle of the observation |
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| 258 | |
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| 259 | * **ROTATION** - *Float* |
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| 260 | |
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| 261 | feed rotation |
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| 262 | |
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| 263 | * **AXIS** - *Float* |
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| 264 | |
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| 265 | ? ask Mark Calabretta |
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| 266 | |
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| 267 | * **TAN** - *Float* |
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| 268 | |
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| 269 | ? ask Mark Calabretta |
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| 270 | |
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| 271 | * **HAND** - *Float* |
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| 272 | |
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| 273 | the sign of the polarisation i.e. 1 for XY and '-1' for YX |
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| 274 | |
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| 275 | * **USERANGLE** - *Float* |
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| 276 | |
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| 277 | A user definable phase correction term |
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| 278 | |
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| 279 | * **MOUNT** - *Float* |
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| 280 | |
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| 281 | ? ask Jim Caswell |
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| 282 | |
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| 283 | * **XYOFFSET** - *Float* |
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| 284 | |
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| 285 | ? ask Jim Caswell |
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| 286 | |
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| 287 | * **XYPHASEOFFSET** - *Float* |
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| 288 | |
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| 289 | ? ask Jim Caswell |
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| 290 | |
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[1858] | 291 | .. todo:: add all sub-table descriptions |
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[1854] | 292 | |
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[1852] | 293 | ======================== |
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| 294 | Mapping to other formats |
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| 295 | ======================== |
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| 296 | |
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| 297 | MS |
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| 298 | == |
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[1854] | 299 | |
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| 300 | MeasurementSets are specifically designed for synthesis data. As such one of the |
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| 301 | main dfferences between the Scantable and a MS is how spectra are stored. |
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[1871] | 302 | An MS stores those in an n_pol x n_channel complex matrix (DATA column) and/or |
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| 303 | a n_pol x n_channel float matrix (FLOAT_DATA column) whereas the Scantable |
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| 304 | stores each polarisation seperately. In case of polarimetry data the (complex) |
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| 305 | cross-polarisation is serialised into real and imaginary parts, e.g. a total of |
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| 306 | four rows would describe one polarisation. |
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