Is Altitude An Historical Artifact

I don't think altitude is an important metric in an automotive GPS as compared to an outdoor/hiking GPS.

My 3790 has altitude readily displayed. And I don't only mean on the satellite reception page (though it is there).
But 3790 you doubtless don't count as a "current automobile GPS".

I think the modern "manuals" are so brief that absence of mention might not mean absence of function.

I suggest you ask here whether any owner of a particular model you are interested can _confirm_ presence of altitude as a selectable display option--and just where it can be displayed.

Confirmation will mean much more than denial.

Living in mountains of western NC, Altitude is often used here

On my 2689 I have a choice of the time, the direction or elevation. It shows in the bottom right hand corner. That location though is also used to show your ETA etc when on a course.. so it is one or the other but not both at any one time.

For what it is worth.. the elevation is not "that" accurate as you will note if ever driving next to the ocean.

There are a few Garmin automotive GPSr's which will display altitude. My 3597 and RV760 are among those that do. A bit of research is necessary to determine availability of that feature in newer models.

Keep in mind that altitude information provided by satellite alone can be off by 20% or so. A good handheld GPS uses a barometric altimeter in conjunction with satellite data to provide a much more accurate reading.

Unfortunately, I'm not aware of any automotive GPSr's with a barometric altimeter.

If price and a large screen aren't big factors, you might consider one of the Montana series. They are basically oversize handheld units but can be equipped with an automotive speaker mount. I frequently use mine in my pickup.

The nuvi 40 was the least expensive of the Essential Series GPS devices when it came out. I did check the manual:

http://static.garmin.com/pumac/nuvi_30_40_50_EN_OM.pdf

and didn't see anything specific about showing elevation although it'd be worth checking page 20 regarding Map Data Layout to see if elevation can be included. Since there's a different setting for Map Detail, the Data Layout may let you change what I would expect the device's ETA when driving a route to possibly elevation. I also wonder when not driving a route whether elevation can be seen.

If the 40 truly doesn't have a means to add elevation to your display, I suggest carefully reading through the owners manuals of the newer models to see if elevation can be displayed with the map. Alternately, asking owners of the newer models could help. Given that the nuvi 40 was an Essential Series model, elevation display options may have been one of the many features not offered except on the satellite display page, assuming it is there.

Not really. There is no reason for GPS provided altitude information to be ten times more inaccurate for a 6000 foot altitude (my home) as for a 600 foot altitude.

And a 20% error on my home altitude would be 1200 feet. The only case I see error of that size in altitude is obvious instances of multi-path reception shortly after turning on the GPSr. I live near a mountain slope, and apparently there are shapes in that slope which occasionally bounce the signal of a satellite just right to have it received "late" thus giving substantial errors in BOTH horizontal position and altitude.

There is a simple geometric reason for GPS altitude information to be a bit impaired compared to horizonal. Your GPSr can't receive signals from satellites below the horizon, so there is inferior triangulation power to get altitude for typical available satellite patterns. But it is nothing like so bad as folks suggest.

There is a more subtle problem regarding the true shape of the geoid (the gravitational potential zero-gradient surface). But if you want to get into that honesty requires mentioning the little detail of datum shifts in horizontal representations for various places in the world.

In 2009 I was on a big cruise ship in coastal Chilean waters and watched with interest as my GPSr clearly showed us traveling not in the waterway but a couple of hundred feet ashore. The map I had loaded was built to a different datum. The funny thing is that the passenger TV channel showed a "where we are" display with the exact same error at the time. Presumably the folks on the bridge were working with better stuff than they showed us.

Different GPS have/use disc space needs/use so rather then build a huge monster to cover all needs and uses, build several specialized models? For example Alt would be desirable for us, but BT, music useless, so I would buy one with less of the junk that Vehicle already has and does better then the GPS

Altitude by satellite is slant range altitude which will always be off from true altitude.

No.

I sail my boat at sea level at all times. However, my Garmin GPS 76 always displays an altitude. Last week it was 70 feet. Happily, it never displays a negative altitude. There are no hills or tall buildings for many miles around, just water.

I bought the Garmin after a Datamarine Loran showed my location as 10 miles inland in Connecticut while sailing Long Island Sound.

dobs108

Location makes a big difference in GPS elevation accuracy. I don't dispute what you say but if you read my post, I said it CAN be 20% off. This is particularly true at or near sea level.

For example, I was in Ocean City MD, last week in a parking lot at the beach. The elevation on my Nuvi 3597 read 102 feet.

I live on top of a ridge at an altitude of 1260' as per the USCGS 7.5 minute quad map of my region. Depending on the number of satellites in view, the elevation displayed by my Nuvi 3597 and RV760 will vary between 970 and 1820'.

On the other hand, when travelling in the mountains, I've often been impressed with the accuracy of my GPS when compared to a roadside elevation sign.

I doubt there is any accuracy differences in the actual altitude calculations but satellite positions almost always result in the elevation result being less accurate.

You can also observe that automotive GPS units always position you on a road, even if the calculation is off a little. Just carefully watch the displayed position when you don’t take the exit ramp that the GPS expected. You need to diverge a hundred feet or so before the display automatically jumps to your current position. That is because it assumes you are on a known road and automatically corrects the apparent position to so it appears you are. That automatic correction is usually not made in elevation.

The altitude of my home displayed on my 3597 is always within 100 of one another, mostly within +-20 ft.

My ham radio transceiver with it's GPS (which I use for tracking) shows the height above sea level of my house to be between 6,210 and 6,270 based on numerous samples. That certainly seems consistent to me. That error is <0.5% with an absolute value of ±40. When at sea level I certainly see a range of about -45 to +45 feet whose range is ±45, just about the same. I regard that as highly satisfactory.

Restating what one of you said, the manuals are inadequate for questions such as mine. I did recheck my Nuvi 40 manual and indeed there was no mention of altitude.

I guess that I'll have to do something that I truly hate: I'll have to go to a store and talk to a salesman.

Thanks all for your suggestions.

Good luck with that. Most store clerks are mouth breathers, now.

The store clerks have no idea about product details. Do your research elsewhere. Some are very open and honest about that.

3790 have the option

I checked with Garmin and if I recall correctly, I was told it was within 50 feet.

Trips through mountainous areas, where peak elevations were posted, showed the elevations were pretty close.

I don't use for anything other than my own interest and amusement. I have it as part of my dashboard .

Under SETTINGS, choose MAPS, click on MAP DATA LAYOUT, then MORE DATA. When you go back to your navigation screen, you should find items on the right side of the screen that you can change. One should be ELEVATION.

Don't confuse "altitude" with "elevation". They are two very different things. Elevation is the height above sea level of the terrain. Altitude, on the other hand, is the distance *above* the local terrain. So aircraft fly at some altitude above the current terrain, but your house is at a given elevation above sea level. Even if you are standing on the top of Mt. Everest, you are still at 0 feet in *altitude*.

Urm... No

The basic kit of instruments for an airplane includes an altimeter, which is generally understood to be reporting altitude.

Just exactly what the number displayed means varies. Generally there is a means to adjust it to a particular barometric pressure. When that adjustment matches local conditions, and when the pressure drop with altitude is reasonably close to the International Standard Atmosphere model, then the number displayed is quite close to altitude above mean sea level. With a different setting of the same adjustment you can get it to display distance above local terrain, but that gets rapidly out-of-date unless your are flying above something very flat. (near airports some organizations used to set it so it would display distance above the runway elevation--I think that practice has pretty much died out).

At higher altitudes, where missing the ground is less of a concern, and missing other airplanes is relatively a greater concern, convention is to set the barometric pressure input to a standard value (the same worldwide). So above the transition altitude at which this is done, the displayed altitude is not particularly close to the actually altitude above sea level, but has the huge advantage that it is matched to what the other airplanes you need not to hit are displaying, even if they did not update to local weather at the same revision as you did.

To be a bit more strict, altitude formally can be described as vertical distance to a given reference. In various practice fields that reference may be commonly understood, and the explicit designation of the reference in use may be omitted.

But saying that altitude always means height above local terrain is wrong according to many dictionaries, wrong according to aviation practice, and not a reliable guide.

That is how it worked on the NUVI 40 and hopefully on the current models.

Again,,, thanks all!

My Garmin Oregon handheld has a barometric altimeter. You can set it so that the displayed elevation is either from the altimeter or from GPS (satellite). The altimeter is calibrated by either either entering the known current barometric pressure at a given location or the known elevation at that your current location. I always calibrate at home just before leaving home for a biking or hiking activity. I know the correct elevation of my home (within 5' or so) based on topo maps, so I use that as the calibration.

It is kind of fun to compare the GPS elevation to the altimeter, and in most cases they are within 10' to 50' from each other. It is also kind of fun to look at the posted track log elevations (based on the barometric altimiter) from my ride or hike compared to the topo map to see how close it is. I have found it to usually be pretty accurate in the first part of my activity, but because of the changing barometric pressure over time and distance and weather, it becomes less and less accurate as the day progresses. In order to keep it accurate, you would need to recalibrate frequently.

is a map feature on my TomTOms, does not come from satellite

That is a nice feature. Google maps will give an elevation profile if you plot a route in bicycle mode. That is a neat feature because Google also has most off road bike trails programmed in their maps as routable in bicycle mode. So you can get a pretty good elevation profile for a bike trail.

One day I noticed that my eTrex Vista HCx was reporting >10,000 ft. above sea level when it should have been ~7,000 ft. Garmin support said that I should re-set the altitude every time the voltage changes, specifically when changing batteries. Apparently the aneroid functionality has some cumulative error and as long as the error is small enough just periodically throw it away. It isn't elegant but it is satisfactory.

At https://support.garmin.com/en-GB/?faq=QPc5x3ZFUv1QyoxITW2vZ6... Garmin states "It is not uncommon for satellite heights to be off from map elevations by +/- 400 ft. Use these values with caution when navigating.".

Reading this thread is getting me high.

I am on the side that as long as we stay on the ground, this should come from maps and not satelite.

Just installed my new DriveSmart 51LMT-S last night. I really like updating it with Wi-fi instead of bringing it to my PC. Unfortunately two of my ham radios require Windoze to update their internals so I can't get rid of Windoze.

And,,, the answer to the subject of this thread is yes, I can have altitude on the main screen.

Thanks all,,,