Scalar data can be plotted as a time series over the time provided by the timestamps of the messages. Then, in the y axis, we can plot our scalar data. The tool for doing so is rqt_plot. It has a powerful argument syntax, which allows you to specify several fields of a structured message in a concise manner; we can also add or remove topics or fields manually from the GUI.
To show rqt_plot in action, we are going to use the example4 node, as it publishes a scalar and a vector (non-scalar) in two different topics, which are temp and accel, respectively. The values put in these messages are synthetically generated, so they have no actual meaning, but they are useful for our plotting demonstration purposes. ...
