Garmin Barometric Altimeter is, Indeed, Worthless

As I commented a few weeks ago, I worried that the barometric altimeter on my GPS unit (a Garmin GPSmap 60CS) was worthless because there are many factors that change air pressure besides a change in altitude (such as holding the unit in a breeze, moving with the unit, changing weather, etc.)

So, I sent a note off to Garmin asking about it, hoping that I was just missing something. Really, why would they include such a feature if it was worthless, much less tout it as they do?

Here's what I sent:

Is there a way to turn off the barometric altimeter, leaving only the GPS altitude? It seems to me (and I'd love to be wrong) that the barometric altimeter is fairly worthless because the air pressure changes with such things like the weather or the unit's position in the wind. I love my Garmin GPS unit, but the altitude part is an unfortunate stain. The altitude data in the track log, which I use to geoencode photos, is essentially random.

I wrote about this on my site and now find that people come to my site via search-engine queries such as “Garmin barometer disable” , so it's not just me that is either ignorant of how to actually use the thing properly, or dissatisfied with it as a solution.

I'd be happy just to disable it, as I can disable the compass (which works wonderfully, by the way 🙂. Is there a way?

Thanks,
Jeffrey

Here's their reply:

Thank You for contacting Garmin International!

I am happy to help you with this. There is no way of turning off the barometric altimeter on this unit. You are correct sir that given the changes you have to calibrate the altimeter just as you would in an aircraft hourly. However, in our units the altimeter is calibrated automatically every 15 minutes to coincide with the GPS altitude.

Sigh.

Silly me for not realizing that I have to calibrate it as I do an aircraft (of course, I make it a point to calibrate my aircraft often, such as before each trip to the corner store).

Apparently, the need to calibrate it hourly (like an aircraft, silly me) is such obvious and common knowledge that Garmin apparently doesn't see fit to mention any of this on their web site or even in the manual! (To be fair, their manual is horrible on all fronts, not just this one, as I've mentioned before... twice.)

I like this GPS unit, but this altimeter and Garmin's documentation of it is ridiculous.


All 21 comments so far, oldest first...

Besides the barometer being relatively worthless, it doesn’t effect any other part of the GPS system right? In other words, it has no effect on your on your GPS determined altitude nor GPS determined position right?

I see it as a bit of a pain to ignore the feature then perhaps, but nothing really detrimental the unit’s primary function. Why would Garmin want to publicize that one of their selling features for this unit is worthless?

— comment by Ben on April 17th, 2006 at 9:59am JST (11 years, 8 months ago) comment permalink

I should be clear that “worthless” is a relative thing — it’s worthless to me, but perhaps not to others. For example, if you leave it in one place, protected from the wind, it will record the air pressure over time, showing plots of the changing pressure. It would be of interest to the student of meterology.

I’d love to just ignore it, but Garmin does not provide an easy interface to the GPS-determined altitude. If you go to the submenu on one specific page, and select the appropriate item, it will show you the current GPS-determined altitude. But all other displays on all other pages are the “worthless” barometer-determined altidude, as well as the altitude recorded in the track log (which is what I use for geoencoding my pics).

I hope one of these days Garmin will update the firmware to include a way to disable the thing.

— comment by Jeffrey Friedl on April 17th, 2006 at 2:57pm JST (11 years, 8 months ago) comment permalink

in your post you complain that “Apparently, the need to calibrate it hourly (like an aircraft, silly me) is such obvious and common knowledge that Garmin…“. However in their reply they state quite clearly that the machine does this automatically: “However, in our units the altimeter is calibrated automatically every 15 minutes to coincide with the GPS altitude.“. I’m not sure why they mention manually calibrating the altimeter then turn around and state it happens automatically but it is pretty clear from that last statement that it’s not something you have to worry about.

The reason they include a barometric altimeter is because the GPS based altimeter is historically not as accurate as the barometric one. I’m not sure why you have such mixed results with it, barometric altimeters are generally more precise than GPS based ones unless you have a very strong GPS signal. I know plenty of people who have used the barometric altimeter on bike rides over varied terrain without any issues with inaccuracies.

— Dennis

— comment by Dennis on April 19th, 2006 at 7:14am JST (11 years, 8 months ago) comment permalink

|> I’m not sure why they mention manually calibrating the altimeter then
|> turn around and state it happens automatically but it is pretty clear
|> from that last statement that it’s not something you have to worry
|> about.

The “automatic calibration”, although not something at all explained, can be turned on and off. When it’s on, the altitude would jump 50+ meters every so often, seemingly randomly. I now know, thanks to the email, that it was trying to coordinate with the GPS altitude at 15 minute intervals. It seems from my experience that it doesn’t “calibrate” only when the GPS signal is strong, which makes it…. what’s the theme here…. worthless.

|> I know plenty of people who have used the barometric altimeter on bike
|> rides over varied terrain without any issues with inaccuracies.

Next time you can get a hold of one (at least, a Garmin one), take it on a bike ride and get going at a mild pace, then rotate the unit to face various directions. You’ll see the barometric altitude change plus/minus quite a distance (say, 20 meters) just depending on the direction the unit’s facing.

My gripe is not that they included a feature that I don’t care for, but that it’s not documented well at all, and that they don’t give an option to turn it off. One would think that these are both fairly trivial to correct. Correcting the first would have caused me to not buy the unit, but correcting the second would allow me to keep the unit without being dissatisfied with it and with Garmin.

— comment by Jeffrey Friedl on April 19th, 2006 at 11:22am JST (11 years, 8 months ago) comment permalink

I’m also frustrated by the almost-useless altimeter.

Have you seen the “60CSx Elevation” thread at Groundspeak Forums? A link to your blog is on Page 3:

http://forums.groundspeak.com/GC/index.php?showtopic=129478&st=100

Your photos are gorgeous. Thank you!

Dick (TracknQ)

— comment by Dick Quinn on May 29th, 2006 at 2:44am JST (11 years, 7 months ago) comment permalink

I have the Garmin Etrex Vista and did not find it’s GPS unit to be very useful. I also have 2 of the GPSIII+ units which I find to be more useful. On my last trip into the hills the Vista wasn’t able to find itself for better than 80% of the trip. We were operating between 9,000 and 10,600 feet on mountain tops and sides – not canyons. The Vista kept complaining it needed a clear view of the sky. I know it doesn’t seem to work well in trees (my 3+ didn’t seem to suffer). Is there a trick to using the vista as a real navigation tool or is it just a flat land toy?

— comment by Jeff on June 28th, 2006 at 4:54am JST (11 years, 6 months ago) comment permalink

Hi Jeffrey, sort of stumbled across your site and I’d like to give you some more info:

for many decades, mountaineers have use barometric altimers (as well as a compass) for finding their way in the mountains.
Yes – you do have problems with changing weather (moving the unit or wind has no influence- at least from my experience)- on the other hand, a changing barometric pressure can alert you on an incoming bad wetaher front.
From my personal experience, the built in barometric pressure sensor in my 60CS is very accurate – even after a day that involves many thousands feet of altitude change I’m within 20 or 30 feet of the altitude that I can derive from a map – including dramatic weather and temperature changes.
The built in barometer was a major reason for me buying the 60CS because my old GPS relied on GPS data for the altitude and in the mountains you sometimes have problems getting a fix on enough satellites for an accurate altitude measurement.

Hope this helps

Daniel

— comment by Daniel on July 27th, 2006 at 4:52am JST (11 years, 5 months ago) comment permalink

Hi Daniel,
Thanks for the comments from an outdoorman’s perspective. Two followup comments from me….

The 60CS remains accurate after a long day of hiking and weather changes becuase, by default, it’s recallibrated via the GPS altitude every 15 minutes. That’s your 15-20 feet of accuracy.

As for how it can change in the wind, since it responds to minute changes in pressure, wind can have a large influence on it. Try holding it out the window of a moving car and turning it this way and that, and watch the altitude display change. I’ve seen it change substantially depending on how I held it in a brisk breeze. Any barometer would act the same way. I just wish that the unit could be set to ignore the barometer and take altitude from the GPS receiver — this would be very convenient on windy days, or on a flight (where the in-cabin pressure simulates much lower altitudes than the 38,000 feet crusing altitude).

BTW, I’ve heard that there are new GPS-related receivers that latch on to a signal much more quickly (1 second vs. 30 seconds). I would like that a lot, so I should investigate if they are used in any hand-held consumer products. I’d appreciate pointers if anyone has any….

Jeffrey

— comment by Jeffrey Friedl on July 27th, 2006 at 5:03am JST (11 years, 5 months ago) comment permalink

Hi Jeffrey. I don’t see how any baro altimeter could be correct without the altimeter setting — which is the local baro pressure corrected to sea level or alternatively, your actual altitude which would let you approximate the altimeter setting — in which case, you wouldn’t need an altimeter. (I’m an ex-military/airline pilot/mechanical engineer so I know this stuff.) Airflow will cause altitude fluxuations as will weather changes, diurnal patterns — as much as 500+ feet in the latter case. It’ll never stay the same. I read the manual for the Vista, hoping that the current altimeter setting (from the local airport) could be plugged in but apparently not. And since the unit automatically uses the GPS altitude to update (override actually) every fifteen minutes, it’d be pointless. And since the GPS altitude error is about twice the horizonal(I think), the baro feature is useless.
Only low flying aircraft (below 18,000 feet) change altimeter settings every hour or so, and if you’re traveling fast, more often than that. Above 18,000, you set the altimeter to 29.92, standard sea level pressure, so that everybody’s altimeters are “on the same page.” When you descend, you set in the current altimeter at your destination. Hope this makes sense. Adios Mike

— comment by Mike on November 6th, 2006 at 5:38am JST (11 years, 1 month ago) comment permalink

Jeffrey,
I’m afriad I don’t see what the problem is. With automatic calibration switched on, the barmoetric altimeter is roughly twice as accurate as the GPS altitude alone. The only exception is immediately after switching on the GPS, when the altimeter can take a minute or two to calibrate itself. See the plot I made with a Garmin Vista.

It is theoretically possible that rapid weather changes could outpace the automatic calibration, but I’ve never seen it happen. The time scale of the automatic calibration is 20 minutes, so the weather would have to change significantly within that time for the errors to become appreciable.

— comment by Tim on November 29th, 2006 at 9:21pm JST (11 years ago) comment permalink

Tim, the problem is that the air pressure around the unit changes when the unit moves through the air (such as when a breeze is blowing, or you’re moving while holding it). Try looking at the altitude reading while holding it in a breeze and turning the unit so that it faces to/from the wind: I tried this once and noticed a 10+ meter change within seconds.

— comment by Jeffrey Friedl on November 29th, 2006 at 9:51pm JST (11 years ago) comment permalink

I have on 60Csx and try to use in airplanes, but after the door is closed, the altimeter set to about 2000 meters over the sea. I recalibrate using the GPS and get the real date. But the airplane is going up and the data is the same, I need to recalibrate every 5 minutes, but is not a good idea.

— comment by Hipolito Gonzalez on January 24th, 2007 at 12:17pm JST (10 years, 11 months ago) comment permalink

Did you get it figured out? You CAN display GPS only altitude. I can do it on my 60CSx. Go to the satellite status page and hit “Menu”. There’s a selection for GPS altitude. Select it and that reading is ONLY from the GPS…no barometer reading is factored in. The only bad thing is it doesn’t update…you just get the altitude/elevation for that exact moment. You have to keep re-selecting “GPS Altitude” for an update. Also, unfortunately, there’s no way to get this displayed in a data field on the other pages.

— comment by Scott on May 29th, 2010 at 11:11am JST (7 years, 7 months ago) comment permalink

My Vista HCx has a barometric altimeter. I used it in the Wind River Mountain at 10,000 to 11,000 feet. When I got home I was surprised to see it show 10,000 feet when I was at sea level or at 6,000 (in the mountains in Oregon).
I guess this might be because I don’t leave the unit for long to save batteries. Of course I should have re-calibrated the unit myself, but I can’t understand why if would be reading 10,000 feet off OR read the same altitude when I change from sea level to say 6,000 feet. To me this makes it unclear what it is doing if I have calibrated it, turned it off and changed elevation and then turned it back on.

As far as auto calibrate option, that seems to be self defeating. (If you set the unit based on the GPS number it will be no more accurate than the GPS unit from then on?) Off course there are times when you don’t know the elevation so using the GPS unit to calibrate is useful. The auto part though adds some uncertainty on what it is using. The advantage of the auto part might be to have the unit do it when it has a good signal which you might not notice if doing it manually.

I do have a Thommen barometric altimeter. It usually works very well even when I don’t recalibrate it. It is also quicker to use (no start up time etc. since I leave my GPS off). I bought a used one to replace one I lost, but it appears to be defective so I can’t use it to verify what is happening with the Garmin, which I expect is less accurate anyway.

(The Land Navigation Handbook states ” If you have watched barometers regularly , you’ll seldom have seen movements of more than 1 inch,. . . in 24 hours .. .which translates into about 40 feet (12 meters) elevation difference at 3000 feet (1000 meters) above sea level. . . .On most days the hourly change in barometric pressure . . .will be a good deal less”) Of course this assumes you are on foot and even so it recommends you reset at known elevations which there are usually a number. And of course occasionally there can be fast moving fronts etc.

I can’t say I put either one out a car window, but I have never read that wind is a factor. Not sure why air pressure would change though from a car and not a natural wind.

— comment by DayHiker on January 16th, 2011 at 6:59am JST (6 years, 11 months ago) comment permalink

Just thought I would add my 2 cents to this this, but ultimately nothing more than that as people seem to have hit all of the major points.

I came across this as a long time Garmin user, from an eTrex Legend Cx –> 60 Csx –> Colorado 300 and now since my Colorado just broke (don’t get me started on that) I will probably buy a GPSMAP 62. Ultimately I have the same problem as Mike. As much as the rest of the information is quite true, honestly who cares if the thing is on or not as long as it is rendering the most accurate elevation reasonably possible. Personally I have found it to be no better or worse in normal circumstances, however I travel quite a bit and in a pressurized plane cabin the thing goes completely nuts. The Garmin logarithms can’t seem to deal properly when the GPS and the barometric altimeter are far apart. I have read in the past that this is due to the fact that the system averages the change from the altimeter to the GPS so that it isn’t either one overriding the other, but that the two work in conjunction. However when you are in a plane all this seems to cause is the GPS to spend several hours giving you the wrong altitude and then several more hours giving you the wrong altitude once you are back on the ground. Yes, yes I know you can manually reset it yourself or go to the satellite screen to see the GPS altitude or set it to “variable elevation mode” to have it log the GPS elevation rather than the Altimeter elevation, but then to the whole point of the thread why have it in the first place if I have to do this kind of thing.

Ultimately this brings me to the main point. When evaluating the GPSMAP 62 series Garmin effectively has 2 models.

GPSMAP 62 (basic) and the GPSMAP 62s. At first glance when you look at the products it seems great, the basic 62 has no barometric altimeter, awesome, however Garmin then proceeds to remove several other features which make this almost unpalatable for the price.

Who the hell doesn’t support “Hi-speed USB” in 2011, especially with 1.7 GB of memory. And no expandable SD slot (maybe that is why you don’t need to Hi-speed)? There are a few other features removed as well, but they are of less importance to me personally.

What I would like is a helix antenna version of the eTrex Legend Cx (or HCx for the new ones). All the features except the compass and barometric altimeter. Since this has been an outstanding issue for several years now I won’t hold my breath though.

NOTE: @Jeff, I have never found the eTrex and the 60CSx to be significantly different for reception in most circumstances except if I tried to put them in my pocket. The patch antenna in the eTrex doesn’t seem to deal with that at all, where the Helix antenna on the 60 would loose some accuracy, but still keep a good satellite lock. the III+ definitely has a better antenna than the eTrex so that is probably the issue.

–Toronto, Canada

— comment by MulderX on February 23rd, 2011 at 1:41pm JST (6 years, 10 months ago) comment permalink

Guernsey Channel Islands UK

The Garmin position on GPS and barometric altitude is quite subtle. A mechanical altimeter is very accurate and reliable once it is set at a local elevation. But it will vary slowly over time in altitude reading if QNH (sea level) pressure drifts. Using a mechanical pocket altimeter such as a Thommen, you would normally expect to reset altitide whenever you reach an accurate known altitude (landmark, map reading). With GPS, when you are wandering through valleys, overhangs, canyons or among trees and buildings the GPS altitude flops all over the place. But the mecanical altimeter stays accurate. At this point it gets a bit tricky because the Garmin philosophy, says, Forget the map or the geopgraphical altitude marker; instead, we’ll feed in a GPS altitude once every 15 minutes and we hope it will be a good one. If it isn’t, then for the enxt 15 minutes your absolute altitude will be out by a fixed amount but your CHANGES of altitude will be very good. In other words you have a smoothing mechanism. This is great for hiking and biking but will not be any use in A presuurized aircraft and definitelly should not be relied on in an unpressurized light aircraft

It is easy to see that in rough terrain where the exposure to satellites changes rapidly, GPS altitudes can change iin value and in accuracy moment by moment; but the barometric reading will be very reliable. I can see that this is the kind of thing that would confuse many people if you put it in the instruction manual. This barometric-GPS feature is excellent for moving relatively slowly over rough terrain. It is totally inappropriate for use in planes and not much use in road vehicles. My Oregon has this feature but my vehicle satnav 1340 does not. And I find that my Thommen (mechanical) barometric altimeter and my Oregon agree closely nearly all the time if each is set and used as it should be.

One final point: checking from time to time on how many satellites, and at what strength, are being picked up by your GPS is good practice.

But the barometric altitude is subject to any kind of change in pressure, such as whether it’s in the wind or shielded from the wind. I suppose you could count on it if you ensure it nor the air around it moves. /-: —Jeffrey

— comment by Peter Hancock on May 14th, 2012 at 11:29pm JST (5 years, 7 months ago) comment permalink

Indeed, the barometric / GPS based altitude has been an issue for me as well. I used to have a etrex legends Hcx (with only GPS based altitude), and I loved to have it during a commercial long haul flight, somehow it calmed me down (I hate flying, and I have to do transatlantic flight very often) to know the altitude and the speed of the planes, which you can do with the eTrex Hcx, even in a pressurised cabin. then I bought the Oregon 300, and bummer, the altitude is based on pressure, so it does not work in long haul flight! And what really anoys me, is that the GPS altitude is indicated on the satelite submenu, but it is not an option in the different fields available on the maps submenu, or a the field trip submenu. Please Garmin, include this data to be available!

— comment by Antoine on July 24th, 2012 at 9:26pm JST (5 years, 5 months ago) comment permalink

Thanks for the info. Saves me the exasperation of contacting Garmin on this. I have a Forerunner 305 as well and it never told me I was 150 meters higher than I actually am – I assume because it doesn’t have a barometric altimeter. I also had an Oregon Scientific device which has a barometric altimeter and it would stay accurate for days or until I took a flight or the pressure changed dramatically. If they have to calibrate the barometric with the GPS altitude every 15 minutes then why don’t they just ditch it and work on an improved GPS altitude algorithm.

Grrrr. And they don’t even give you the option of turning it off – oh and it doesn’t actually calibrate properly every 15 minutes!

— comment by Paddy O'Reilly on May 31st, 2013 at 11:09pm JST (4 years, 6 months ago) comment permalink

I’ll just say this quick, I am a graduate student studying in GPS/GNSS area.

Point positioning in your GPS is not very good, and the elevation accuracy is particularly horrible.
The response i read from germin said that their device AUTOMATICALLY calibrates to the gps elevation (every 15min).

Although there is “drift” (corrected by the gps elevation calibration) the barometric altimeter can detect smaller changes in elevation more accurately than the gps would be able (in PPP).

So i am not sure why everyone wants to turn it off?

— comment by Phil on September 25th, 2013 at 3:30pm JST (4 years, 3 months ago) comment permalink

Comments on several subjects, from SW Los Angeles area:

As with your other correspondents, I have been asking Garmin for years to provide an option to only use gps-determined altitude and ignore the barometer. But to no avail. An altitude estimate is needed to compute lat/long. When the barometer-determined altitude is incorrect, the lat/long computation is also incorrect. The 60CSx appears to use a sophisticated long-time constant filter to correct the barometer back to reality (as it should); this usually works fine if altitude changes slowly as when hiking. In a pressurized airplane the 60CSx works fine for take offs and landings but probably has relatively large lat/long errors at altitude (where it doesn’t usually matter).

The 62s really falls apart when moving fast. It’s a catastrophe in a pressurized airplane. It shows altitude as 21,000ft when landing at a sea level airport!! The lat/long error at landing was 450ft–or maybe we actually landed on the adjacent corn field and I didn’t notice? While on the subject of the 62s, it is less sensitive than the 60CSx in head-t0-head comparisons-losing lock in many cases while the 60CSx hangs in easily. The 62s has a miserable tracklog management system, is hard to read without a backlight, even in daylight, and battery life isn’t that good. Luckily, I got it at REI and they will take it back.

— comment by Bob K. on November 23rd, 2013 at 10:53am JST (4 years ago) comment permalink

Very interested in the 15 minute reset to the gps altitude. Negatively. For accuracy of mountain trail profiles altimeter is more accurate than gps due to the signal angle relative to horizontal. If you can calibrate barometric to a known topo point you are more accurate. According to Garmin technical.. Weather changes take place over many hours even in storm front situations. Your baro altitude is better was topo points give you steady offset checks wh4n you evaluate the track. Resetting the baro to the less accurate GPS altimeter value every 15 minutes is not a good thing. It is removing the better differential data for less accurate.

— comment by George Leaf on October 20th, 2015 at 5:28am JST (2 years, 2 months ago) comment permalink
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