New GPSs with Barometric altitude

[thomas28]

I am looking to buy a new gps, but I don't understand why some of the higher end new units, like the Garmin 60csx have a barometric altitude sensor built in. A satellite gps 3D triangulation gives you altitude....at least it does on my old, old unit (pre-WAAS, pre-21st century). The barometric altimeters that I'm familiar with are not all that accurate and they change as the weather changes. Don't the current gps designs show good altitude data?

 

Perhaps I'm missing something?

 

Regards,

Tom C.

Edited December 6, 2007 by thomas28

[abadrs]

My Magellan explorist 600 has that feature. It says per the manual must be recalibrated every 2-3 hours. So defenitly the Elevation figured by the satelites is defenitly more accurate. The funny thing the manual really doesn't tell you how to calibrate it. I'm not really sure what altitude you put in ?

[gallet]

I am looking to buy a new gps, but I don't understand why some of the higher end new units, like the Garmin 60csx have a barometric altitude sensor built in. A satellite gps 3D triangulation gives you altitude....at least it does on my old, old unit (pre-WAAS, pre-21st century). The barometric altimeters that I'm familiar with are not all that accurate and they change as the weather changes. Don't the current gps designs show good altitude data?

 

Perhaps I'm missing something?

 

Regards,

Tom C.

 

Current GPSr's show excellent altitude accuracy but they are not as 'fine grained' as a barometric altimeter. A baro altimeter will show your changes by the metre but gps accuracy is only about plus or minus 5 metres.

 

With regards to accuracy, aeroplanes use baro altimeters and I don't see many of them crashing into hillsides so they must work pretty well. Yes a baro altimeter needs to be calibrated constantly just like the ones on aeroplanes.

[Tahosa and Sons]

Not using the altimeter much was one of the reasons that I went to the Legend HCX when I upgraded from my old Vista. As long as I can plot my UTM's on a Topo map I'll have a close enough altitude fix.

[+Renegade Knight]

...Perhaps I'm missing something?...

 

They are more accurate when calibrated. If you actually need detailed and accurate elevation information thats the way to go. The GPS without the baramoter does give you an elevation. However it's a ball park at all times with more variablity in the readings. For most caching purposes that's good enough.

[+boda]

I do not calibrate mine very often. I use it to get a rough idea of what altitude I am at, or to note the amount of altitude gain or loss during a hike. I have never had much luck with using it for the few caches that give an altitude as part of the description.

 

Off topic: I was on a hot air ballon flight one time and the pilot, another cacher and I all had GPSr. It was interesting to compare altitudes that were over 100 feet different.

[+ArmandoM]

The barometric altimeters that I'm familiar with are not all that accurate and they change as the weather changes.

Regards

Tom C.

 

So, how can I tell when is going to rain??

[thomas28]

The barometric altimeters that I'm familiar with are not all that accurate and they change as the weather changes.

Regards

Tom C.

 

So, how can I tell when is going to rain??

 

You get wet.

 

Actually, If you are just sitting around and not changing altitude, the barometric altimeters make good weather barometers...because that's what they are.

 

Regards,

Tom C.

[oxothuk]

AIUI, GPS elevation is very accurate over the long run (assuming the geoid model is correct in your neighborhood) but has a lot of random error variation from minute to minute. Barometric elevation, on the other hand, has relatively little random error variation from minute to minute but degrades over a span of hours as the weather changes.

 

For that reason, combining a barometric sensor with automatic calibration based on GPS elevation should give the best of both worlds. The barometer smooths out the random errors, and the GPS auto-calibration corrects for barometric drift.