Gerund present: "Заметив"

Question

I have a question about a Gerund: "Заметив" and how you as russian speakers would translate it in this context. It is derived from the verb: "заметить".

Example: Заметив как из другого вагона выходит брюнетка с мальчиком школьного возраста.

Answer 1

You could translate it as

Noticing a brunette with a boy of school age leaving another car...

Or, if the action described is in the past, then

Having noticed a brunette with a boy of school age leaving another car...