[KaiserPro]

You can't use visual key-points to navigate over open water.

You can use other things like Visual Odometer, but there are better sensors/techniques for that.

What it can do, if you have a big enough database onboard, and descriptors that are trained on the right thing, is give you a location when you hit land.

[Tostino]

That's exactly what the comment you replied to was describing.

[TeMPOraL]

> You can't use visual key-points to navigate over open water.

No, but you can use the stars. Even during the day.

[KaiserPro]

true, but that requires an accurate clock, and specialised hardware. Ideally you also need to be above the clouds as well.