POSITION IN TUNNEL

Which nuvi do you have? Some of the newer models do estimate your position within certain tunnels even though there is no satellite signal to give an exact location. It is my understanding that this function does not work in all tunnels, so it must be tied to the map data. If you ever need to stop in one of these tunnels you would see your position continue to change even tho you are stopped.

I have a Casio Exlim-H20G digital camera that has a GPS chip for geotagging. It is interesting that it also has a motion sensor so it can estimate your coordinates from your last known position when you are inside a building, tunnel, cave, etc. They call it Hybrid GPS. I don't know of any automotive GPS systems that have this capability.

The product literature for my TomTom states that it contains an accelerometer it can use to estimate its position during brief periods when it cannot get a GPS fix.

You don't mention what model Nuvi you have but a number of them obtained this ability with a firmware update over the past number of months. I never noticed that the speed was assumed to be 35 MPH but will keep an eye on that in the future.

The other thing I believe happens that didn't before is that the Nuvi will switch to "night mode" when you enter the tunnel and goes back to "day mode" (if it's daytime) when you exit it.

I appreciate the input on this.

The factory GM unit in my Vette does that same thing by using the motion speed and direction sensors built into the car when no GPS sat signal is available such as in a tunnel or parking garage. It also uses that quite accurately to follow and show the vehicle's position on the display map when first taking off until the system locks on to the sats. It will show on the display that no GPS sats but will still show the car moving along on the map. The first time I use the car for the day it may take a minute or two to lock on to sats but the position still follows along as I drive,

Thanks for this information. I didn't realize that any of the automotive GPS systems had this capability. It seems like it would be a real advantage in the "urban canyons" where the GPS signal typically is lost or badly degraded. It would also be helpful in parking garages.

Yes it is very sophisticated and really spoils a person once they have used it for a while.

The nav system is completely integrated into the car's computers and other systems. It not only displays the nav turn direction, distance and the name of the street you will turn on in the navs screen display but it also displays that same info in the heads up windshield display so you never have to take your eyes off the road. That is a big help when in heavy traffic in LA or Phoenix areas.

It even adjusts the display automatically for day or night using the cars light sensors that run the headlights but also adjusts the nav prompts volume based on the cars speed and if the top is up or down.

I haven't taken notice of any estimates with this unit yet but it was always my understanding that you need a GPS that is connected to the car's speed sensor like my Pioneer head unit to get accurate results. I'll test out my unit this weekend. Interesting...

Unless the tunnel is very long, my unit shows my movement in the tunnel. I have only lost the signal a few times.

My Zumo 665 has, for the last 15 months since I owned it, continued through every tunnel I've traveled in Pittsburgh and Western PA. It does lose position when in parking garages and around other structures so there is no accelerometer in the Zumo, of course I didn't expect there to be.

I regularly travel through a few different tunnels so I'll have to pay attention to the speed on a few of them to see if it is a set speed or varies.

So if I get stopped in a tunnel and the vehicle on the GPS screen continues, do I push on the brake harder?

Sure, why not? You're already stopped, so at worst you'll just get a free leg workout...

I have a nuvi 760, and I've noticed that it gives me an estimated position when I go through the tunnels into Manhattan as well. I don't know that I've updated the software on it since I bought it 3 years ago.

...uses the speed that was last known before sat reception was lost through the tunnel until it gets a signal again, then adjusts accordingly. It assumes you don't break through the tunnel wall and proceed along the roadway.

My son is a mechanic for a Lexus dealer. The nav systems in the Lexus update position based on speed etc. when they loose satellite signal. He mentioned that they were running a vehicle on a dynamo and even though they weren't changing location the nav system showed them zipping along right through buildings etc. Sounds even stranger than watching your track over the ground while flying.

that's really interesting.

That's funny (and interesting).

I've also noticed changes within the Google nav app and found that Google updated the app to provide for a night mode transition (dimming the screen) when inside a tunnel. I also see the vehicle progress while passing through tunnels using the Google app.

Though primitive in its limited hard drive map architecture, the Alpine in-dash GPS in my 1999 Acura was able to fill in gaps with motion sensing. I believe it actually had a gyro in it as well as an acceleration sensor.

Larry

Larry.

Most modern navigators will simply presume you were driving at a constant speed and continue to follow the road for some time before reporting lost satellite signals.

Most likely Alpine took the speedo and compass input from your car and used that - Navigation without GPS augmentation is known as 'dead reckoning' and if tied to a map the term 'with map matching' is added to the description.

In the early '90s I was involved in a project with General Motors Research Labs and we deployed a proof-of-concept system in a fleet of 100 Oldsmobile Toronado rental vehicles that we equipped with an in-vehicle navigation system that was ONLY dead reckoning with map matching - given the cost of GPS receivers back then it was the only way to go. We used the CRT-based touch screen that the car had which was used to control the aircon and radio and tied it to the cell phone as well.

The project was called 'TravTek'. It was deployed in Orlando, Florida.

The cars were equipped with a data communication system (there was no available cellular data back then) that reported location and speed to a central database in real time which was combined with traffic condition input from other sources and was then sent back out to the vehicles on a return channel - truly dynamic traffic services.

The return data also allowed us to see where each active car in the fleet was, which way it was heading and how fast as well as what the vehicle's destination was along with some of the vehicle's operating parameters.

We used to sit in the control centre and get a kick out of sending false data to cars in the fleet making them drive in circles as the in-vehicle routing algorithms tried to avoid the false traffic congestion data we were broadcasting.

The system was implemented in a '386 that was installed in the center console.

In one prototype we installed a GPS receiver, but only overlayed the reported location on the car's map display. We did not use GPS for the location function.

Calibrating the system involved manually entering an address using the touch screen - it (usually) recalibrated position whenever the car turned a corner (hence the need for map matching).

I must admit that it all worked fairly well, though from time to time the car thought it was driving across Lake Apopka and some of the proposed routing did require stunt driving skills (they still do).

This research system was the underpining of what eventually evolved into GM's Onstar system and quite probably those ubiquitous navigators we all own as well.

Interesting enough I got involved with this project as the result of prior work done in 1989 on a similar system (in terms of the position determination and data gathering, but with different goals) we did for CalTrans in LA called Pathfinder.

Predated Nuvi, Garmin did have few GPS that had 'dead reckoning' feature that can estimate your location without GPS signal. I don't think new models have that feature any more because they are not mentioned in the spec.

The Streetpilot 2650 had a dead reckoning feature

That is, it now keeps the icon moving through the tunnel.

Haven't had a firmware update in a long while, so I assume it's in the map code.