I have a small robot (turtlebot3) with a Lidar. For aa demonstration I would like to process the data coming from the lira in the following way:

- Pay attention only to a range of angles (e.g. -15 degrees to +15 degrees)
- Filter it into

a) distance to obstacle

b) rate of change of a)

c) rate of change of b)

I am assuming that this is elementary and there are nodes/libraries in ROS that do just this. I am not asking for code but pointers to where to look and what to read. Thanks for your help!