Plot Axes

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3.3.1.3 Plot Axes

The X and Y axes of a plot are selected by clicking on the Plots > Axes tab on the left side of the plotms window, and choosing an entry from the drop-down menus below X Axis and Y Axis (see Figure 3.2). Possible axes are:

Scan — The scan number, as listed by listobs (§ 2.2.6) or the data summary in plotms (§ 3.3.1.8).
Field — The field number, as listed by listobs (§ 2.2.6) or the plotms data summary (§ 3.3.1.8).
Time — The time at which the visibility was observed, given in terms of calendar year (yyyy/mm/dd/hh:mm:ss.ss).
Time_interval — The integration time in seconds.
Spw — The spectral window number. The characteristics of each spectral window are listed in listobs (§ 2.2.6) or the plotms data summary (§ 3.3.1.8).
Channel — The spectral channel number.
Frequency — Frequency in units of GHz. The frame for the frequency (e.g., topocentric, barycentric, LSRK) can be set in the Plots > Trans tab (§ 3.3.1.9).
Velocity — Velocity in units of km s^-1, as defined by the Frame, Velocity Defn, and Rest Freq parameters in the Plots > Trans tab (§ 3.3.1.9).
Corr — Correlations which have been assigned integer IDs: 5 = RR; 6 = RL; 7 = LR; and 8 = LL.
Antenna1 — The first antenna in a baseline pair; for example, for baseline 2-4, Antenna1 = 2. Antennae are numbered according to the antenna IDs listed in listobs (§ 2.2.6) or the plotms data summary (§ 3.3.1.8).
Antenna2 — The second antenna in a baseline pair; for baseline 2-4, Antenna2 = 4. Antennae are numbered according to the antenna IDs listed in listobs (§ 2.2.6) or the plotms data summary (§ 3.3.1.8).
Antenna — Antenna ID for plotting antenna-based quantities. Antennae are numbered according to the antenna IDs listed in listobs (§ 2.2.6) or the plotms data summary (§ 3.3.1.8).
Baseline — The baseline number.
UVDist — Projected baseline separations in units of meters. Note that UVDist is not a function of frequency.
UVDist_L — Projected baseline separations in units of the observing wavelength (lambda, not kilolambda). UVDist_L is a function of frequency, and therefore, there will be a different data point for each frequency channel.
U, V, and W — u, v, and w in units of meters.
Amp — Data amplitudes in units which are proportional to Jansky (for data which are fully calibrated, the units should be in Jy).
Phase — Data phases in units of degrees.
Real and Imag — The real and imaginary parts of the visibility in units which are proportional to Jansky (for data which are fully calibrated, the units should be Jy).
Flag — Data which are flagged have Flag = 1, whereas unflagged data are set to Flag = 0. Note that, to display flagged data, you will have to click on the Plots > Display tab and choose a Flagged Points Symbol (§ 3.3.1.7).
Azimuth and Ant-Azimuth — Azimuth in units of degrees. Azimuth plots a fiducial value for the entire array, while Ant-Azimuth plots the azimuth for each individual antenna (their azimuths will differ by small amounts, because each antenna is located at a slightly different longitude, latitude, and elevation).
Elevation and Ant-Elevation — Elevation in units of degrees. Elevation is a representative value for the entire array, while Ant-Elevation is the elevation for each individual antenna (their elevations will differ by small amounts, because each antenna is located at a slightly different longitude, latitude, and elevation).
HourAngle — Hour angle in units of hours. This is a fiducial value for the entire array.
ParAngle and Ant-ParAng — Parallactic angle in units of degrees. ParAngle is the fiducial parallactic angle for all antennae in the array, while Ant-ParAng plots the parallactic ange for each individual antenna (their parallactic angles will differ by small amounts, because each antenna is located at a slightly different longitude, latitude, and elevation).
Row — Data row number. A row number corresponds to a unique time, baseline, and spectral window in the measurement set.
FlagRow — In some tasks, if a whole data row is flagged, then FlagRow will be set to 1 for that row. Unflagged rows have FlagRow = 0. However, note that some tasks (like plotms) may flag a row, but not set FlagRow = 1. It is probably better to plot Flag than FlagRow for most applications.

If the data axis selected from the drop-down menu is already stored in the cache (therefore implying that plotting will proceed relatively quickly), an “X” will appear in the checkbox next to In Cache?.

For relevant data axes like Amp and Phase, the user will be presented with the option to plot raw data or calibrated data. This can be selected via a drop-down menu called Data Column, located directly under the drop-down menu for X or Y Axis selection (see the Y axis in Figure 3.2). To plot raw data, select “data”; to plot calibrated data, select “corrected”. Note that this choice will only have an impact on a plot if a calibration table has been applied to the measurement set (see applycal, Sect. 4.6.1).

If a data model has been applied to the measurement set (e.g., with setjy, Sect. 4.3.4) it can be plotted by selecting “model” from the Data Column menu. Finally, to plot the differences between the calibrated data and the model, select “residual” from Data Column.

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