The truth about GPS in cars. I get a lot of questions about this. But first: Should you make GPS a mission-critical criterion in the selection of a new car? I’d suggest not.
Can I add GPS to the car later?
Sure: If you’re buying a car without GPS, there are several options. In the aftermarket industry you can get them to perform day surgery and install a GPS head unit, so you won’t have to futz with suction cups and cables.
But why not just use Google Maps or download an app from a GPS nav specialist like Tom Tom for your smartphone?
How good are GPS units in cars?
They’re all as accurate as each other from a navigational perspective. The location and speed computations are all done off the back of of the US Military’s Navstar Satellite (GPS) system, so accuracy doesn’t vary between units.
And the map data generally all comes from a government entity – so it’s all the same for particular places. What does vary is the user interface and the software routines driving the navigation. So they look different and use different logic.
In my view car companies are generally shit at this – really counter-intuitive and clunky. The best in-car executions are in fact licensed direct from (say) Tom Tom.
Map upgrades are a disaster for in-car GPS, and the older the car the more epic the disaster. Some older cars are no longer supported, so upgrades are just unavailable. And if they are, and they are only available from a dealer, they are likely to cost a bomb, leaving you in a situation where you could by half a dozen standalone Tom Toms for the price of one in-car update.
GPS for dummies: There’s a Navstar Satellite Constellation in medium earth orbit, 20,200km overhead. It’s been there nearly 40 years. The system only needs 24 satellites to function brilliantly – but there are 31 currently in orbit. So it’s all stocked up on satellites.
Your GPS receiver only needs to see four satellites to resolve the four big questions: Latitude, longitude and altitude, plus precise time. Once you know that, speed and navigation are all computations done based on firmware on the device in your car or in your hand.
Satellite signals do have a problem punching through dense foliage. So big, thick tree canopies are bad, and if you’re deep in a canyon with only a narrow slit of sky overhead, that can compromise satellite visibility.
You might not be driving in the Amazon any time soon, and you might think you don’t drive in canyons very often, but I’d suggest you are wrong (about the canyons, at least). Canyon driving is a very ‘first world’ scenario indeed.
The most common place to encounter canyon-type satellite compromises are when you are driving in cities.
It is one of the most outstanding developments of the 20th Century. Of course in the boonies it’s always nice to know how to move with a map and compass, because batteries go flat, but the earth’s magnetic field is somewhat more dependable.
Any claim by a carmaker that the underlying dodginess of their GPS unit in your car is because satellites are dropping out is almost certainly uninformed nonsense. A lame-arsed, technically incognizant attempt to brush you off.
GPS dysfunctionality is far more likely to be the result of their hardware or the firmware just being shit and not working properly.
Time for some mad science. Dr Who meets Einstein and makes GPS work.
The Navstar satellites are further than we are from the earth’s gravitational mass. Therefore (brain-bending time) time on the satellites runs at a faster rate than it does for us. The effect is only minor – but without correcting for it we’d never get a decent answer to where we are on the planet.
I just use the Tom Tom app on my phone. It’s free. You get free lifetime map upgrades (dear car dealers, stick that where the Pope fears to wash) and that freeness comes with 75 kilometres of free nav per month.
After that, if you go with the paid version of the app, which is under $100, the nav is unlimited. This has the added advantage of coming with you after you park the car – which is quite useful if there’s an on-foot component to your destination, or if you fly into an unfamiliar place and rent a car.
And, finally, data: Doesn’t mobile phone GPS app-based nav use data? Won’t it rack up a big data bill if you thrash it your GPS app on your phone?
Ahhh – no. It doesn’t and it won’t. It works like this: The maps and the navigational software live on the phone – there’s no cloud connectivity or mobile data component to running the maps and navigating.