Nuvi Question about Staying on Roads

At least responding to point 2) - the Nuvis have a bit of a pre-track programmed in. It keeps things smoother, particularly if you've been headed in a constant direction for awhile. I've noted its speed sensitive too. Once it figures out you're throwing tricks its direction, it jumps back to where it really is. Drive into a long tunnel and watch

I don't have a clue why but my 660 does the same thing.

Other nuvi owners? Do you see this behavior in your GPSr?

B-Photog

The city relocated a road recently. Yhe Nuvi's "jump" to the road as the mapped road is approached.

Having just spent several hundred miles putting Street Pilot through it's paces everywhere, I have to offer what I observed on this very same subject.

I noticed that the unit tries to follow it's mapped roads even when you're really off the road. It only deviates, albeit jumpy, when you go off to somewhere it doesn't have a road to track on. This usually happens, as I watched, when you go into parking lots or off the roads it "knows". It ultimately does update to it's actual location which typically shows you in the middle of nowhere, but close to your road. It stays on the road until it gets just so far away from it that realizes that you aren't there anymore. I suspect about 75 to 100 feet. Anyway, just an observation.

Rick

Also remember GPS units do not have pinpoint accuracy. The accuracy varies to within 15 feet to hundreds of feet depending on reception, weather or the moon and stars. So if you choose a car as your vehicle the Nuvi has no reason to think that you're no on a road. So lane changes aren't gonna get noticed. Sometimes going from the main road to the service road doesn't get noticed unless you go from the 3rd lane on the main to the first on the service road. Once you get far enough off track, then it will realize that you aren't just changing lanes or drunk driving and update your location.

My wife says to stay on the road I need to look out the window rather than at the GPSr!!!

That is a great comment. Something my wife might say.

I did notice this past weekend that I was driving in a field according the the Nuvi 660 but I was really on the road. I thought it might have been bad mapping data since the road has not be relocated.

The GPS units will tell you what lane to stay in on highways. For example, if you are driving down Interstate 420 (inside joke there) and it says, "In 1.5 miles take a left on Interstate 420", it is usually a situation where the road will vere right or left with another road going off. Make sense?

The GPS units also only know the roads that are on the map. If a road is moved, a temporary road built to avoid construction or such, it will show you driving through a field.

Mapping errors happen, and they happen often. We need to remember the GPS is a tool, NOT an autopilot. I recently read (on another site, sorry kids) about a man suing Garmin (or Tom Tom or someone) because he drove off a bridge that wasn't marked on the GPS. Obviously, we do have to use common sense and remember the GPS is a tool, NOT an autopilot!

Just remember a road GPSr is made for driving and will lock your position on to the closest road on the screen. It will only unlock itself when your position is too far off.

If you ever own a mapping GPSr. It will display its current fix instead of locking to a road. Using a mapping GPSr for driving will drive some people crazy because the cursor is not always on the center of the road.

I always wonder about GPSr accuracy. I think up to 3 meters might be conservative. I used the Garmin Edge (same Sirf chip) on a bike ride and the bike path is less than 10 feet wide. On my round trip, the tracks are pretty much parallel each other and never crossed. If the accuracy was 3M. The tracks should have crossed. To make thing interesting, the path is also parallel the power lines the whole length.

I’ve had a Nuvi 660 for a month or so now, and I’ve noticed the same thing.

The Nuvi 660 wants to keep you on a road even if you are not on one, like when you turn into a parking lot. You can be in a parking lot, driving parallel to a road, and the Nuvi will place you on that road. It will do this despite the accuracy of your position, e.g. the accuracy can be 50 feet, and you can be 100 feet from the road, and it will still want to put you on the road.

I’ve also noticed that if I make a turn, the Nuvi will keep me in the original direction I was traveling for quite some time past the intersection, and then my position will jump to the new road I just turned on.

I’ve compared the behavior of the Nuvi 660 with the built-in nav system in my wife’s Lexus. The system in the Lexus handles these situations far better than the Nuvi does. If you turn into a parking lot, that is shown immediately. Likewise for turns. On the way to work this morning, we took a freeway on-ramp that paralled the road we were on for a few hundred feet. The nav system in the Lexus placed us on the ramp far, far sooner than the Nuvi did. The Nuvi placed us on the original road until we were well down the ramp and quite a distance from the original road.

When giving directions in these situations, the Lexus works much better. If you are off the road (e.g. in a parking lot), the Lexus just says “proceed to the route and then the guidance will begin” or something like that. It will wait until it knows you are on a road before trying to provide guidance. The Nuvi, which is placing you on whatever road you happen to be traveling parallel to, will try to give guidance based on being on that road, which is not correct.

Likewise for the freeway ramp I mentioned above. The Nuvi would have given directions based on you being on the original road rather than the freeway ramp, while the Lexus would not have done that.

It seems the algorithm in the Nuvi places too much weight on placing you on a nearby road no matter what, while the Lexus trusts the position more.

that the Lexus also has dead-reckoning tied into the transmission or the tires, no?

This feature is only available on the high-end Garmin units and it makes the position accuracy much more precise and available when the GPSr can't lock onto any satellites.

dd

Yes, the Lexus does have dead-reckoning.

Based on how the Nuvi will suddenly jump your position from one spot to another, I’m guessing that it is software, and not the accuracy of the GPS position, that is causing this. It seems that the Nuvi should trust the GPS position more, rather than a software algorithm.

On another note, the Lexus seems to pull in the satellites much faster as well. Turn on the car, and the “GPS” indicator lights up, indicating it has received a GPS position, almost instantly. The Nuvi takes a while. I wonder if the Lexus keeps the GPS receiver up and running even when the car is off?

and it's keeping the GPS status alive all the time. One more "parasitic drain" on one's car battery.
( http://www.batterystuff.com/tutorial_battery.html#8 )

dd

I'm had it jump ahead too and I'm not sure why. But I use my 680 off road for Geo caching. I have to switch away from the map to the coordinates sreen and look at actual coordinates if I'm any where near a road because Auto GPSr are made from driving not walking (sounds like a good country song title). So it is trying to place which road you are on not give you the actual position on it map since it thinks you should be driving on a road. It is hard being a GPSr gussing what we humans are tryng to do all the time.