Intrigued, I looked into the basics of "line-scan vision systems".

TIL about an industrial inspection application where your line camera is scanning objects passing by on a conveyor. Since you can never guarantee a rock-steady conveyor speed, you need real-time control of the scanning speed based on the current conveyor speed (using encoders) [1]

I see that the bulk of the article is about somehow using math for estimating the train speed so that the scanning can be interpreted correctly.

[1] this camera vendor has an explanatory video that explains the need for an encoder around 4:15. https://m.youtube.com/watch?v=E_I9kxHEYYM&t=35s&pp=2AEjkAIB