National Radio
Astronomy Observatory

3.3.1.7 Plot Symbols

Plot symbols are selected in the Plots > Display tab. Most fundamentally, the user can choose to plot unflagged data and/or flagged data. By default, unflagged data is plotted (the circle next to Default is checked under Unflagged Points Symbol), and flagged data is not plotted (the circle next to None is checked under Flagged Points Symbol. We note here that plotting flagged data on an averaged plot is undertaken at the user’s own risk, as the distinction between flagged points and unflagged points becomes blurred if data are averaged over a dimension that is partially flagged. Take, for example, a plot of amplitude versus. time where all channels are averaged together, but some channels have been flagged due to RFI spikes. In creating the average, plotms will skip over the flagged channels and only use the unflagged ones. The averaged points will be considered unflagged, and the flagged data will not appear on the plot at all.

A selection of None produces no data points, Default results in data points which are small circles (blue for unflagged data and red for flagged data), and Custom allows the user to define a plot symbol. If Custom plot symbols are chosen, the user can determine the symbol size by typing a number in the blank box next to px or by clicking on the adjacent up or down arrows. Symbol shape can be chosen from the drop-down menu to be either “circle”, “square”, “diamond”, or “pixel” (note than “pixel” only has one possible size). Symbol color can be chosen by typing a hex color code in the blank box next to Fill: (e.g., “ff00ff”), or by clicking on the ... button and selecting a color from the pop-up GUI. The adjacent drop-down menu provides options for how heavily the plot symbol is shaded with this color, from heaviest to lightest: “fill”, “mesh1”, “mesh2”, “mesh3”, and “no fill”. Finally, the plot symbol can be outlined in black (if Outline: Default is checked) or not (if Outline: None is checked). Note that if “no fill” and Outline: None are selected, the plot symbols will be invisible.

Finally, unflagged data points can be given informative symbol colors using the Colorize parameter. By checking the box next to Colorize and selecting a data dimension from the drop-down menu, the data will be plotted with colors that vary along that dimension. For example, if “corr” is chosen from the Colorize menu, “RR”, “LL”, “RL”, and “LR” data will each be plotted with a different color. Note that, currently, colorize and plotting flagged data appear to be incompatible; a plot can only include one of these special features at a time.

More information about CASA may be found at the CASA web page

Copyright © 2010 Associated Universities Inc., Washington, D.C.

This code is available under the terms of the GNU General Public Lincense