Comments on: Garmin Barometric Altimeter is, Indeed, Worthless http://regex.info/blog/2006-04-16/179 Not a photo blog, but sometimes I play one on TV Sat, 06 Sep 2008 03:18:06 +0000 http://wordpress.org/?v=2.0.12-alpha by: Hipolito Gonzalez http://regex.info/blog/2006-04-16/179#comment-3127 Wed, 24 Jan 2007 03:17:48 +0000 http://regex.info/blog/2006-04-16/179#comment-3127 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. 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.

]]> by: Jeffrey Friedl http://regex.info/blog/2006-04-16/179#comment-2829 Wed, 29 Nov 2006 12:51:52 +0000 http://regex.info/blog/2006-04-16/179#comment-2829 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. 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.

]]> by: Tim http://regex.info/blog/2006-04-16/179#comment-2828 Wed, 29 Nov 2006 12:21:47 +0000 http://regex.info/blog/2006-04-16/179#comment-2828 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 <a href="http://timgiles.free.fr/garminalt.htm" rel="nofollow">plot</a> 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. 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.

]]> by: Mike http://regex.info/blog/2006-04-16/179#comment-2755 Sun, 05 Nov 2006 20:38:52 +0000 http://regex.info/blog/2006-04-16/179#comment-2755 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 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

]]> by: Jeffrey Friedl http://regex.info/blog/2006-04-16/179#comment-2348 Wed, 26 Jul 2006 20:03:09 +0000 http://regex.info/blog/2006-04-16/179#comment-2348 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 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

]]> by: Daniel http://regex.info/blog/2006-04-16/179#comment-2347 Wed, 26 Jul 2006 19:52:20 +0000 http://regex.info/blog/2006-04-16/179#comment-2347 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 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

]]> by: Jeff http://regex.info/blog/2006-04-16/179#comment-2319 Tue, 27 Jun 2006 19:54:55 +0000 http://regex.info/blog/2006-04-16/179#comment-2319 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? 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?

]]> by: Dick Quinn http://regex.info/blog/2006-04-16/179#comment-1939 Sun, 28 May 2006 17:44:20 +0000 http://regex.info/blog/2006-04-16/179#comment-1939 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’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)

]]> by: Jeffrey Friedl http://regex.info/blog/2006-04-16/179#comment-1069 Wed, 19 Apr 2006 02:22:10 +0000 http://regex.info/blog/2006-04-16/179#comment-1069 |> 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 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.

]]> by: Dennis http://regex.info/blog/2006-04-16/179#comment-1068 Tue, 18 Apr 2006 22:14:38 +0000 http://regex.info/blog/2006-04-16/179#comment-1068 in your post you complain that "<i>Apparently, the need to calibrate it hourly (like an aircraft, silly me) is such obvious and common knowledge that Garmin...</i>". However in their reply they state quite clearly that the machine does this automatically: "<i>However, in our units the altimeter is calibrated automatically every 15 minutes to coincide with the GPS altitude.</i>". 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 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

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