what is the rolling_pts parameter in differential_drive?

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This isn't clear in the code, and took a little reading around, but rolling_pts is used in the pid_velocity.py file to set how many past velocity measurements are used to calculate the average velocity. For example, setting rolling_pts to 2 will make PID controller average the 2 latest velocity measurements to create what it considers the "current velocity".

The name is a little misleading, but now that I know what it does, it is called "rolling" because it is a rolling average. I assume this is done because only using the single latest velocity measurement, instead of an average, could be a bit noisy in some situations, so using the average smooths things out a bit.

p.s. the way I figured this all out was a reference to rolling_pts in this slightly related page.