Yet, More etrex Vista Altimeter Quetions.

[+jtice]

Well, this is about the third post ive had on this topic,,,

 

As some of you already know, i have been having trouble with the elevation readings on my Vista. I can calibrate it to my driveway elevation of 1,045 feet, sit it down, and 5 minutes later , it says 897 feet.

Plus I have had it say 800 feet at the bottom of a hill, drive up the hill, and it actually drop a couple feet,, then read about 812 feet at the top of the hill, when really, the hill was at least 80 - 100 feet higher.

Garmin has said,,, that I am either reading the information incorrectly, (oh come on now!,, I'm not a complete idiot, and i can read. whats to misread?), or that the unit is defective. They said they will fix it for free, but I can bring myself to let it go for a couple weeks.

 

So, heres a couple questions.....

1.) In your Opinion, is it broke?

2.) Lets say I calibrate the unit while sitting still in my driveway, with it attached to my bike, and go riding. Does the wind rushing over the unit effect the elevation much? More than say, 15 feet?

I have noticed little things can effect it, such as, queezing the unit in my hand, the elevation will go down.

3.) I noticed that when I goto the satillite page, and ask it to display the GPS elevation, that is VERY accurate. Is there a way to tell my Vista to use the satillite elevation all the time, instead of the pressure reading?

 

--- Thanks alot, all of you here on the forum are alot of help. !!!

[+GeneralBracket]

1. Not in my opinion.

 

2. It could, but not much. However, altitude is based on barometric pressure. Any change in that regardless of wether you're moving or not will change the altitude reading.

 

3. Not exactlly. But if you turn on Automatic Calibration it uses GPS elevation to refine the barometric elevation, which makes it more accurate over time (according to the manual).

 

I've seen the problem you mention when I turned off Automatic Calibration. When on, the barometric elevation and GPS elevation are very close to eachother. To my mind I don't think barometric pressure is terribly reliable for calculating altitude without frequent calibration. Barometric pressure is constantly changing with the weather, which in turn throws off the calibration.

 

DISCLAIMER: I really have no knowledge of the internal workings of a barometric altimeter. I am however I fairly smart guy so I suppose you could call my theories educated guesses.

[+Bloencustoms]

Try disabling the auto calibration, then manually calibrate the altimeter. Check the reading over time and see if they are more stable. The auto calibration feature will combine the gps elevation with the barometric elevation, and will take a while to settle down. I find that with auto cal. off, if I manually calibrate, it remains pretty accurate untill the barometric pressure changes. The only way to get a real accurate elevation is to measure the gravity at your location.

 

"Searching with my good eye closed"

[+apersson850]

I've tried both with and without auto-calibration. But for ordinary use, I think auto-calibration works best. It's not always the correct altitude that's displayed, which is most obvious when it becomes negative near the sea level, but it is not that dramatically off as it can be, when using the air pressure alone.

 

Anders