In-car GPS Navigation
Wednesday, October 28, 2009 at 10:39AM 
There's been a lot of hype as of late over the new GPS-enabled phones now offering apps with turn-by-turn directions. New York Times writer Eric Taub wrote a really good shoot-out piece on the subject. The article, and the discussion as of late, have focused primarily on consumers' smart phones -- namely the iPhone -- offering these new apps that will give you turn-by-turn while you're driving.
The problem I've heard with these -- and witnessed first-hand with dedicated dashboard or hand-held GPS devices -- is their latency in providing the turning directions when you actually need to turn. This is important when you're approaching an off-ramp or a turn that immediately follows another turn. During the latter, the device is trying to calculate whether you actually made that first turn in order to reposition you for the next turn. This also comes up when you stray from the given directions by bearing right or left. The device does not immediately recognize that you have strayed from your path and continues to give false directions for a few seconds. When you're driving 60 miles per hour, a few seconds can mean the difference between making an important exit or missing it, possibly adding undue time to your trip.
The reason for this conundrum is technical in nature. It's also speaks to the very under-publicized benefits of in-car or manufacturer-installed GPS navigation systems. GPS devices that are build into cars before they're sold are wired into two valuable components of your automobile. First, these devices are connected to your odometer/speedometer. This is a huge enhancement, because the GPS device then knows exactly how fast and how far your car is traveling at any time. This is unlike hand-held devices that rely solely on the signals from at least 3 GPS satellites to determine the car's speed and distance traveled. You see this really come into play when you drive through a tunnel. The hand-held device loses its signal from the satellites, while the in-car device still "knows" where you are in the tunnel, based on how far and fast you're traveling. You've probably seen this with hand-held devices when your car icon suddenly "pops" to the other end of the tunnel.
Second, because an in-car GPS device doesn't have the burden of needing to be small and portable, it can -- and does -- also connect to an in-dash compass. This allows the device know when the car has made subtle turns or slow-speed turns that a hand-held device would take much longer to determine. If you divert from your suggested route with a hand-held device, it takes a few seconds for the device to realize it, as the display "pops" your car icon to the new road onto which you've now turned. This is also the case when you make a shift from a local lane to a parallel express lane on a major highway. The in-car device detects that slight directional shift, whereas the hand-held device might miss it -- and the correct exit.
Don't get me wrong, I do think the hand-held devices are great. They empower consumers to have more information on the go. Also, using these portable devices allows you to update their maps much more frequently than in-car devices, which require a new data DVD that only comes out around once per year at a cost of up to $150 each time! They also allow for overlay of more types of information than in-car devices: traffic, weather, restaurants, gas prices, etc. But for pure directional accuracy, nothing beats the in-car device.
Matthew Snodgrass
Interesting development ... Google has announced that they're going to be offering free turn-by-turn directions for Android-based phones, initially the Motorola Droid. This will undercut what folks like Garmin and TomTom do with their devices. However, this is an odd move, since Google would essentially be biting the hand that feeds them, as TomTom owns Tele Atlas, which is one of Google Maps' major map data suppliers. We'll see how this plays out.
car, gps, iphone, mattsnod, navigation, turn-by-turn in Technology 
Reader Comments (2)
Don't forget the third option - portable, dedicated GPS navigation devices. I would rank them nearly equal to in-dash systems in terms of accuracy. Mine will calculate my rate of speed which is generally only a few MPH off, give or take as well as my direction. However, you're right - it doesn't perform "dead reckoning" which is the temporary ability to monitor your position and maintain your route using your speed and last known position.
It does offer the added benefit of portability, though.
I love taking my portable navigation system with me when I travel as I don't have to learn how to use the rental car company's device (nor pay for it).
-jf.
@jf: You're right on the rental car issue. I cringe whenever I rent from Hertz (which I like) and have to use their NeverLost GPS system, which I've termed "SeldomLost." It once put me 3 blocks away from the Denver Convention Center. It's a convention center, people ... not a hot dog stand.