So I decided to look into how Tesla does alternate routes (I know, late) fully expecting to see they just get a few alternatives from Google and that's it and... nope, there's nothing like it!
Instead they grab a route from google (if online nvigation enabled), and then feed that into tesla maps service (in the cloud). And that maps service returns possible alternatives (deduced by unknwon means). But that's not all!
A lot more interesting is that in addition to that they also query that service for "what are the parking lot outline at my location" and "hey, for this route I have, what else do I need to know".
This last part is interesting, because it tells the car in great detail map corrections like "there's a stop sign here", "crosswalk there" with great accuracy.
Also other useful information like lane info, directions of travel and whatnot.
And speed (to show you yellow/red path)
When people say "my car took the same route as before and this time drove better" - the map updates like this help immensely and is probably why.
And overall it seem to be updating certain elements in near realtime. This also includes rough road patches and such.
The car also feeds things like detected speed limits and realtime speeds there in return every 2 minutes or so.
Certainly helps keep maps a lot more current than even regularly updatable maps in cars are. And only relevant sections at that.
Basically it's like a waze service, but for the autopilot. Here is the output I got for the route from 35.93486,-84.014374 to 35.810833,-83.993889 the other day: pastebin.com/Z3ivF3Cu
the edge ids are relative to Tesla in car maps so the car knows what property to update.
And if you pay close attention, a bunch of elements presented list Tesla as the source.
Looks like pastebin hates long pastes.
so here's a link that actually works. Thanks, rentry!
rentry.co/sgodk
btw I guess important corollary (that we mostly knew about) is - Autopilot performs better when you have a route set because if you don't, it does not fetch this "information about route ahead".
Keep this in mind with your testing.
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