If you want to learn to play the double bass and need to learn fingerboard geometry first and don't have access to a good double bass teacher, you might just get a cheap bass guitar and figure out, where the notes are, (open strings, intervals, positions, ear training, playing melodies and basslines to simple songs), and then meet a qualified teacher later, to teach you, how to apply, what you already know to the double bass.
If you already know where the notes are and what you want to play, you can focus on posture, sound production and basic technique and squeeze much more out of every single lesson, even if only every couple of weeks with a teacher on person.