GPS nuvi problem

cheri1122

Veteran Expediter
Driver
Has anyone else had a problem with their Garmin Nuvi [mine is a 2555] randomly displaying a frozen speedometer & miles to next turn, and both the bottom corner options limited to 3 choices: direction of travel, time of day, elevation? I want to choose time for the left one, but I want 'miles to destination' in the right corner, and it isn't an option when I touch it. Can't find anything in settings that applies, either.
I've searched the online owners manual and FAQ, no help. It's done this before, and will reset itself at some point, but I'd like to know how to change it before it decides to reset. Thanks for any suggestions, I'm frustrated.
 

Turtle

Administrator
Staff member
Retired Expediter
When was the last time you updated the firmware?

Push and hold the Power button to turn it OFF, but keep holding for 10-30 seconds (10-15 will usually do it) until it self-restarts. That's a soft reset. It should restart and reload the firmware and all the map data. That should fix the problem.
 

cheri1122

Veteran Expediter
Driver
Soft reset done, map data reloaded, no change, sigh. [Can't be sure about the speedometer, it's correct at 0, lol] still getting just 3 options for the bottom corner fields. [Why 'elevation' is a desired option for a vehicle is beyond me] :mad:
 

cheri1122

Veteran Expediter
Driver
I can see where 'elevation' might be desired for those who carry their GPS while hiking, [I love when I put 'Lowe's in the search, find one 1 mile away, select, and it asks Driving? or Walking?] but it just doesn't seem to be a more popular choice than miles to destination, or time to destination - both of which have disappeared without warning from the choices.
 

Turtle

Administrator
Staff member
Retired Expediter
Elevation is important with hikers and bikers, but in a motor vehicle it's of limited use because of how elevation is determined in vehicle GPS units. The GPS units used by hikers and bikers use a barometric altimeter which, if properly calibrated by hand, will be within 10 feet of actual geoid (sea level).

With vehicle GPS units, elevations are based on an ellipsoid (a mathematical representation of the earth's shape, rather than the geoid) and is more closely tied to the map data than the actual elevation. It has to do with how many satellites the receiver is picking up, as well. Because the map data is accurate, the satellite data doesn't need to be all that accurate insofar as altitude, but does need to be accurate on horizontal positions, and if the GPS unit accurately knows where you are horizontally, the map takes care of the altitude, even though the actual altitude displayed on the unit will be the ellipsoid, which can easily be +/- 400 feet. The closer you are to sea level the more accurate it is, but in the Rockies your GPS could say you are at 6300 feet but you could actually be anywhere from 5900 to 6700 feet.

So, with a vehicle GPS, what happens is, the satellite receiver determines your horizontal with high accuracy, and then based on the map data and the ellipsoid, determines rather accurately your elevation, and then after that initial satellite fix your altitude is merely a relative altitude based on the mathematical ellipsoid, rather than on actual relative altitude to sea level. You can solve this dilemma by driving to the Equator, letting your GPS unit get an accurate fix on the satellites, and then never ever turn off the GPS unit. Or by getting a barometric altimeter GPS unit.

Sooo, in a vehicle, not only is elevation not a particularly popular display choice, it's virtually useless. :D


As to your current situation, the next step is to ensure the latest maps and firmware have been installed. After that, a hard factory reset would be next, but that will, absolutely, wipe out any saved Favorites.
 
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TruckingSurv

Seasoned Expediter
Turtle, I haven't found what you are saying at all with my Garmin units, when you pass an elevation sign, the GPS unit is almost always within a few feet of the posted summit sign. It is true that GPS measures ellipsoid heights, BUT you can convert those to orthometric heights (commonly called sea level heights) by applying a geoid model of the differences between the two height systems. I am pretty sure Garmin has some sort of a geoid model loaded, but they don't say which one, likely EGM08 as that is the one that works with the native satellite datum, but really irrelevant as ALL geoid models in the last 20 years have less error than an autonomous GPS position does. It is true that number of satellites affects the horizontal and vertical accuracy, but usually these days there is quite a few satellites tracked and unless in an urban or natural canyon with lots of trees or perhaps a tunnel, the number tracked should be sufficient.

I have never seen a handheld GPS that has a barometer built in, mine doesn't, it computes an elevation the same as both of my vehicle units.

I do own an electronic Suunto barometer/altimeter and a watch that has functions that measures atmospheric pressure and to which you can calibrate to a known elevation or pressure, pick one as they are interrelated.

I am a professional land surveyor as well as a CDL driver, in the surveying world with high end equipment, I regularly obtain "sea level" elevations to better than a few centimeters using ellipsoid heights combined with a geoid model. This is with equipment that is in a different league than vehicle or handheld units, but none the less, the principles are the same and the horizontal and vertical error of most consumer models should be under 10 meters most of the time.

To say GPS can't produce correct heights is incorrect information.

The elevation on my Garmin Nuvi is useful to me when crossing a pass or knowing when I reach the forecast freezing elevation, whether I am running on a flat grade, up, down, etc. are all informative uses in a vehicle navigation unit.

Shelby
 

TruckingSurv

Seasoned Expediter
Cheri, can't help with your specific issue, BUT will say my Garmin Nuvi has frozen more than once, rebooted at the most critical times, etc., to where I have been ready to heave it out the window. It seems to have most issues in the truck mode, been running it lately in my personal vehicle in auto mode and no issues, BUT I regularly also update the firmware, so it is possible that Garmin fixed whatever was causing the bad behavior? All I can suggest is keep it updated and do the reboots when needed, I know they can be frustrating, trust me I went round and round with tech support and they replaced the unit twice, the problem wasn't a specific unit IMO, BUT bad or buggy firmware/software to which of course they wouldn't admit to.

Shelby
 

RoadTime

Veteran Expediter
Owner/Operator
As to your current situation, the next step is to ensure the latest maps and firmware have been installed.

I had that happen a few times in the past, I think the final remedy was what Turtle said. After updating (and keeping updated) I have not seen that issue come back.
 

cheri1122

Veteran Expediter
Driver
Ok, I guess I need to dig out the correct USB cord for connecting it to the 'puter.
My one experience with updating the maps was horrendous: took hours, and ran into data over charges, so I haven't done it again.
What it's doing now is something it's done before, but it fixed itself. I've had no other problems with it, so I kind of forgot to figure out what caused it.
 

Turtle

Administrator
Staff member
Retired Expediter
Turtle, I haven't found what you are saying at all with my Garmin units, when you pass an elevation sign, the GPS unit is almost always within a few feet of the posted summit sign.
Your use of "at all" combined with "almost always" is puzzling, as "I haven't found... at all" implies never, and "almost always" implies not always. In any case, +/- 400 feet hardly mean that it absolutely, positively will be off by 400 feet every time, all the time, no exceptions. I have seen mine read within 5 or 10 feet of a summit sign, and I've also seen mine show more than 300 feet off from a summit sign, including those same variations at the same sign.

I am pretty sure Garmin has some sort of a geoid model loaded, but they don't say which one, likely EGM08 as that is the one that works with the native satellite datum, but really irrelevant as ALL geoid models in the last 20 years have less error than an autonomous GPS position does.
Back in June I sent an e-mail to Garmin Support and specifically asked how they model the difference between geoid and ellipsoid. The reply that I got wasn't all that helpful, and it was 5 paragraphs as opposed to the two paragraphs found in a July update to their FAQ, but either the reply came from the FAQ, or the reply I was sent was later incorporated into it. The e-mail also noted that the barometric altimeters are accurate to +/- 10 feet, and displays an accuracy of up to the hundredths of an inch of mercury. even after inputting a known altitude or normalize air (despite one being able to infer from the accuracy of the altitude that the barometer would be accurate to one thousandth of an inch of mercury). Garmin does not publish accuracy for the barometric pressure sensor, but they do publish the accuracy of the barometric altimeter readout. The accuracy is published as 10 feet with proper calibration. I usually get better than 10 feet with the GPSMap, as well as I usually get far better accuracy than 400 feet with the Nuvi.

But I wouldn't use either for a surveying job, and not just because I don't know the first thing about surveying. Or maybe that's the first thing you should know. I dunno.

I have never seen a handheld GPS that has a barometer built in, mine doesn't, it computes an elevation the same as both of my vehicle units.
Garmin has more than 20 handheld units which incorporate a barometric altimeter, including the Montana, eTrex, Oregon, and GPSMap series. I have a GPS 64 series unit.

To say GPS can't produce correct heights is incorrect information.
Yes it is. I never said that, however. I did say that vehicle GPS altitude readings are virtually useless, and I said it because they are not accurate enough to be relied upon. As Garmin will tell you straight up, "Garmin's devices are designed as recreational GPS devices, as an aid to navigation. They should not be used for any activity requiring precise measurements such as surveying or weather prediction."

The elevation on my Garmin Nuvi is useful to me when crossing a pass or knowing when I reach the forecast freezing elevation, whether I am running on a flat grade, up, down, etc. are all informative uses in a vehicle navigation unit.
I use it for the same things, but I don't for a second believe that if it says I'm at 3252 feet that I think I'm at exactly 3252 feet. I'm going with somewhere in the neighborhood of +/- 200 feet, which is what "virtually useless" means. If it's not accurate, just how useful can it be on which to rely?
 

Turtle

Administrator
Staff member
Retired Expediter
My one experience with updating the maps was horrendous: took hours, and ran into data over charges, so I haven't done it again.
The firmware updates aren't bad, but the map updates can be a couple of gigs or more and can take hours to download. If cell data bandwidth caps are an issue, I'd wait and do it when you have a good WiFi connection. I have unlimited data, but for a Garmin map update I'll wait until I'm at home on the WiFi to do it.
 

Turtle

Administrator
Staff member
Retired Expediter
My one experience with updating the maps was horrendous: took hours, and ran into data over charges, so I haven't done it again.
The firmware updates aren't bad, but the map updates can be a couple of gigs or more and can take hours to download. If cell data bandwidth caps are an issue, I'd wait and do it when you have a good WiFi connection. I have unlimited data, but for a Garmin map update I'll wait until I'm at home on the WiFi to do it.
 

TruckingSurv

Seasoned Expediter
Turtle, of course I wouldn't use a Garmin on the dash for a surveying job, it is just a tool to navigate close to start using the proper tools for the task, I do load survey points in my Nuvi via a GPX file and it will talk me to where I need to get out and start looking for a monument, the same as if it were an address, very handy tool for returning to old projects where you have an old project with coordinates already established.

I have no idea what Garmin is blabbing about with the 400 feet. Totally ignoring the ellipsoid-geoid difference anyplace in the lower 48 in the USA will only introduce about 1/4 that error. In other places on their own website they state 15 meters is an average accuracy and that seems to be in the ball park I experience, I think they are just doing a CYA statement. If memory serves correctly under 50 feet is what I see when compared to known elevations also. If there is 400 feet of error it has to be from not tracking adequate satellites.

The closer you are to sea level the more accurate it is, but in the Rockies your GPS could say you are at 6300 feet but you could actually be anywhere from 5900 to 6700 feet.

This is not correct, the sea level accuracy is dependent on the geoid model in use and NOT the current location of the GPS unit. Totally ignoring the geoid model will produce elevations closer to "sea level" in certain locations because the separation is less, BUT it is not necessarily tied to costal regions. Here is the link to the National Geodetic Survey geoid contour map for the current model. http://www.ngs.noaa.gov/GEOID/GEOID12/maps/GEOID12_CONUS.png

You will note that the NW is actually closer to zero difference than say Florida, BUT assuming a device has some version of a geoid model built in, this doesn't really matter as the device will then make the correction from ellipsoid to sea level heights within the error budget of the geoid model and the error budget of the measured ellipsoid height by the device.

So, with a vehicle GPS, what happens is, the satellite receiver determines your horizontal with high accuracy, and then based on the map data and the ellipsoid, determines rather accurately your elevation, and then after that initial satellite fix your altitude is merely a relative altitude based on the mathematical ellipsoid, rather than on actual relative altitude to sea level. You can solve this dilemma by driving to the Equator, letting your GPS unit get an accurate fix on the satellites, and then never ever turn off the GPS unit.

This makes no sense to me. ALL GPS units that I am aware of and I have used many, from handheld to vehicle navigation to high end $20000 survey units, measure the location of the receiver in a XYZ Cartesian system based at center of mass of the earth, and then through use of a defined ellipsoid convert that to Latitude, Longitude and Ellipsoid height, accuracy in these systems is identical for a given satellite constellation rather you be at the equator or in the USA someplace. Then to that resulting ellipsoid height a geoid model is applied to produce a more meaningful height that we refer to as elevation relative to "sea level". They are more correctly called orthometric heights but "sea level" is more easily understood and is usually interchangeably used. There is often also a datum transformation behind the curtains too if you want to see anything other than WGS84 Latitude and Longitudes, but for driving down the street that may or may not be important, at least until we start letting the GPS drive the vehicle. At that point the road maps/database and the navigation system definitely need to be playing from the same sheet of music so to speak.

Link to a tutorial that explains this in more detail with some diagrams: Tutorial: Elevation Correction and the Geoid | Education | UNAVCO

Shelby
 

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xmudman

Veteran Expediter
Owner/Operator
My GPS doesn't have elevation. I know when I'm in high places when the octane number starts to drop and I have to buy midgrade to keep the same performance I get in flat land :p
 

cheri1122

Veteran Expediter
Driver
The firmware updates aren't bad, but the map updates can be a couple of gigs or more and can take hours to download. If cell data bandwidth caps are an issue, I'd wait and do it when you have a good WiFi connection. I have unlimited data, but for a Garmin map update I'll wait until I'm at home on the WiFi to do it.

Last time, I called Verizon and was pretty upset over the data charges [to update the maps], and they said just bring it into one of their stores and they'll do it, lol.
I didn't though, I wanted my GPS working like NOW, and it is - the updates cleared the problems. :)
 
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