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.
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?
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.
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
|> 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.
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)
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?
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
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
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
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.
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.
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.