So currently I am kinda on a mission to upgrade my old in car satnav with newer maps (I drive an Alfa Romeo 159 with Connect Nav head unit). I searched far and wide, through highs and lows of the Internet and I couldn't find any way, or any one that has managed to successfully convert any map format into an old NAVTEQ format.

The only useful piece of information that I found is that it uses the same format as the RT3 maps used by Peugeot and Citroen. That means the the successor o NAVTEQ, HERE Technologies is responsible for making those maps, since they were created in 2017.

My question is the following:

Is it possible to convert any map format (preferably Garmin (.img) or OSM) into an old NAVTEQ one, or the one that HERE used in 2017?