Android: speedometer app. Isn't using gps really that bad?

Question

satellite navigation

Essence of the question: I would like to ask, because. not so long ago I read and talked with the android guys.
After all, there are a lot of applications for cars in the market: hud, speedometer, gps speed, etc. I would like to slightly modify all the solutions to suit my tasks (I myself am not an android and will not be developing) ...
All the fear is dissuaded from the idea: they say gps is not very reliable, throw the bad out of my head, and so on. And error, etc.
Well, OK. Let's say it is.
BUT!
After all, there are a lot of applications for measuring speed in the market, and there are many with 4-5 * and tens of thousands of downloads and good reviews. They also use 99% gps.
Or are there some tricky schemes for using the accelerometer? + after all, the same racelogic also uses gps, but they are not used by schoolchildren on the frets)
Just wondering how such an unreliable thing can get good reviews? )

Answer 1

GPS has two problems:
- initialization time from 10 seconds to several minutes;
- actively eats the battery. True, when driving, this is not critical if charging is at hand.
An accelerometer is not suitable for measuring speed - it measures acceleration. If you remember the school physics course V = V0 + a*t. That is, in order to measure the speed with it, you need to know the initial speed, before the moment of acceleration. So it will only go to refine the GPS data.

Answer 2

Maybe it's because they use both gps and an accelerometer?
Don't be afraid, just check. Make a working concept when only GPS works. Maybe he will suit you.

Answer 3

they say gps is not very reliable

why is he unreliable? it just gives you coordinates with an error (at times when it can catch a signal). You can also take the coordinates of the towers, but the error is even greater.
Accelerometer is not for coordinates.
You have not voiced the requirements, maybe you want to do indoor navigation using gps ...