Is there a function for identifying the location of these circled parts of a signal waveform

Question

It might be called the "foot" or "leading edge" but I don't think that's fully correct.enter image description here

I've tried the 1st and 2nd derivative but the peaks are slightly off of this location.

Answer 1

Those circled points are quick (maybe even discontinuous?) increases in the function's derivative. I'd try to locate them by identifying points where both

• the first derivative is positive, and
• the second derivative is large and positive

using some finite difference approximation to estimate the derivatives.