Using a GPS for fuel economy

[GasSavers_maximilian]

My TomTom allows me to add map corrections and share them with others. Yesterday I changed a curve that had one end blocked off. Odd, since the same basic change done elsewhere in the same town around the same time was in the maps.

It definitely has some weird stuff, design wise. I can't set it to not quiz me every time as to whether or not to avoid unpaved roads. I live off of one, so every single time it pesters me. I also can't make it lock the owner's information. It can take a password, but then I have to enter it each and every time it starts up. I just want to require a code to change the info!

[JanGeo]

Sounds like MapShare which comes at an addition cost as I recall.

[GasSavers_maximilian]

Yes, MapShare. Good news is it's free. I assumed it wasn't too but I checked into it.

[theholycow]

+1 on the GPS being the best clock.

Here's how GPS technology works (very simplified): The satellites all broadcast the time with very fine resolution, and very accurately. Because that broadcast moves only as fast as light, there is a very tiny difference between each satellite's broadcast in how long it takes to reach you. Your GPS compares that and calculates how long it took to arrive from each of 4 or more satellites, and therefore its distance from each of those satellites. It figures its position based on that.

Therefore, the time has to be perfectly synchronized and measured in each satellite and in the GPS receiver, which assures you that it's got the best time.

That also means that if your GPS is having trouble acquiring its position, you should make sure it's got the time set correctly (or nearly so); that helps it make sense of the satellite signals more quickly.

[theholycow]

Originally Posted by bobc455

I will also occasionally use it to double-check the routes that I take every day. For example it did give me an alternative route from the gym to work that I'd never have considered, which is actually shorter & quicker than my old route (hence saving me some gas).

I've found that Google Maps (not Google Earth) by far the best for this purpose. I used to like Microsoft Streets & Trips best, but now with Google Maps you can drag your route to your preferred roads. Especially combined with satellite imagery, this makes it the perfect tool for detailed fine-tuning of a daily route.

[GasSavers_maximilian]

Any way to set max speed in Google Maps? If there is I've been missing it.

[theholycow]

No, setting different speeds for different types of roads was one of the things I liked about Streets & Trips, but with Google Maps ability to graphically manipulate routes there's no need for it.

[GasSavers_maximilian]

Originally Posted by theholycow

+1 on the GPS being the best clock.

I always assumed GPS units were just digital clocks updated from an atomic clock every so often. Is that true? The satellites have atomic clocks I know, but clearly the unit doesn't!

[theholycow]

The GPS time is updated from the satellites every second. That's how it knows where you are.

[GasSavers_maximilian]

Now that's interesting. Since there are delays in the communication from the satellites, and it also relies on those delays to compute the position, I wonder how they accurately figure out exactly what to set the time to? Pretty easy if you know already almost exactly your location or the time I guess.