How to filter and smooth the curve into straight line

Question

enter image description here In this first picture, the line represents the velocity change during the taking off period of the plane. I want to smooth this curve and replace it with straight lines and then to identify the trend of every section.

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In this second picture, I draw what I want to get and replace all this signal into several straight lines.

What I have tried: 1 Smoothing technique : Savgol_filter; Gaussian filter Python model tsmoothie 2 Line simplification algos Ramer-Douglas-Peucker algorithm

However, it is hard to find a appropriate parameter to identify all the time series. (This means to define the rise,flat and fall period) However this change of velocity has a pattern to follow: normally it gets two or three platforms.

I don't know if there exists some paper or algorithm to handle this kind of problem

Here are other examples of time series to model enter image description here

enter image description here