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Old 04-03-2013, 11:03 AM   #7381
dvmvm
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GPS elevation

Quote:
Originally Posted by SteveAZ View Post
I appreciate the feedback. It would be nice if Garmin documented how things work, however....

My understanding is that:
  • Setup - Altimeter - Barometer Mode = Fixed Elevation => the barometric pressure displayed being that of the direct reading of the barometric pressure sensor compensated for by the "calibrated" elevation (refer to auto calibration on/off) and that it expects that elevation to be fixed; i.e. the GPS is stationary. This is the mode you might use while at a fixed location to apply the barometric sensor as you would a barometer. My experience with other Garmin units with barometric sensors (e.g. 76Csx) in this mode is that the track logging and altitude display are not the GPS derived elevation but still the barometric pressure sensor derived elevation.
  • Setup - Altimeter - Barometer Mode = Variable Elevation => the barometric pressure displayed is simply compensated to the "calibrated" elevation.

GPS derived elevation is much less accurate than the horizontal GPS accuracy (usually about 2x or somewhat more than horizontal) and it depends on satellite position geometry. The "auto calibration" takes the average of the GPS derived elevation over time and "calibrates" the barometric altimeter to this elevation periodically to compensate for the normal barometric changes.

This works very well except for when you are in aircraft or even when the unit is mounted in the wind stream or behind a windshield on the moto where the pressure is not the static pressure and it can cause errors of more than a hundred feet or even much more. Forget about it in a pressurized cockpit where it is useless. I fly aircraft for sport (ultralights, sailplanes, other) and for a lot of these applications either don't need a aviation GPS or they are fix mounted in the aircraft and I'm just looking for a handheld so I can download the track logs easily when I get home.... Hence the desire for a more accurate track log then I get from the barmoteric sensor derived altitude. My experience has been that the GPS (actually GNSS) elevation in an aircraft with the antenna in a good position does much better than the barometric sensor derived elevation - particularly in these newer units that aren't just GPS but use other satellites like Glonass or Galileo (GNSS - Global Navigation Satellite Systems)... It would probably be a very different case if we could plumb a good static pressure source to the handheld but that's not practical.

Maybe this is different on the Montana but it's how it works in the 76Csx and since the setting fields are the same, I'm skeptical it's different. It's very easy to test. Just take the unit up in a commercial aircraft and see whether the elevation maxes out at 7.5-8.5K' instead of 30-40K'....
Its even simpler to test (fw 4.70):
  • Go to the tripcomputer and select the two data fields "elevation" and "GPS elevation". Switch autocalibration off.
  • With Setup - Altimeter - Barometer Mode = "Variable Elevation" the "elevation" data field uses the barometric sensor. You can press with your finger on the 4 little holes on the back of the Montana. You will see that the elevation datafield changes while pressing the holes firmly or softly, indicating that the "elevation" data field uses the baromatric sensor.
  • With Setup - Altimeter - Barometer Mode = "Fixed Elevation" you will see that the "elevation" and "GPS elevation" data fields are identical. Pressing the 4 holes does not change anything.

Anyway, I see no reason why this contradicts your findings for the barometric readings. I think the behavior for barometric reading and the one for elevation can co-exist.
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Old 04-03-2013, 04:06 PM   #7382
caver
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SUCCESS!!!! Thanks Mac and Emmbeedee (for sharing your Montana wisdom). My computer stopped communicating last night with my Montana. Same thing today when I got home from work. I tried reloading the USB driver from the Garmin site with no luck. So I reluctantly did a GPS master reset and that fixed the "device not recognized" problem. I deleted that other CityNav.img file from the SDcard and just to be safe loaded a big chunk of Mapsource Topo West to the internal memory instead of the SDcard. I should probably be brave and load some of Topo East but I won't be riding in that area and feel like I'm pushing my luck with a trip rapidly approaching. The only thing I have to fix is my old shortcut to disable CN when I wanted topo maps. I used Mapsource too for the record. I haven't got the hang of BaseCamp yet.
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Old 04-03-2013, 05:16 PM   #7383
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Quote:
Originally Posted by caver View Post
SUCCESS!!!! Thanks Mac and Emmbeedee (for sharing your Montana wisdom). My computer stopped communicating last night with my Montana. Same thing today when I got home from work. I tried reloading the USB driver from the Garmin site with no luck. So I reluctantly did a GPS master reset and that fixed the "device not recognized" problem. I deleted that other CityNav.img file from the SDcard and just to be safe loaded a big chunk of Mapsource Topo West to the internal memory instead of the SDcard. I should probably be brave and load some of Topo East but I won't be riding in that area and feel like I'm pushing my luck with a trip rapidly approaching. The only thing I have to fix is my old shortcut to disable CN when I wanted topo maps. I used Mapsource too for the record. I haven't got the hang of BaseCamp yet.
If you used Mapsource, your map file will be called gmapsupp.img and should immediately be renamed to something else before you upload another file and overwrite that one.

Just call it Topo West.img or something else which indicates what map it represents, and you'll be ok. You can do this with Windows Explorer or the program below.

JaVaWa Device Manager does a really good job of telling you what your map file is comprised of, and it allows you to rename it properly, both in the file name and the map's name as indicated in the gps dialogs.
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Old 04-03-2013, 11:33 PM   #7384
Hayastani
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The audio output from my Montana 600, via an Autocom system, is barely audible at anything above approximately 40mph. I have adjusted the earpieces to the optimum position, the Autocom is at its highest setting as is the volume control on the Montana. Does anyone know of a piece of kit that would significantly increase the volume? Preferably something that would simply plug in to the current set up. Thanks.
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Old 04-04-2013, 02:57 AM   #7385
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Quote:
Originally Posted by Hayastani View Post
The audio output from my Montana 600, via an Autocom system, is barely audible at anything above approximately 40mph. I have adjusted the earpieces to the optimum position, the Autocom is at its highest setting as is the volume control on the Montana. Does anyone know of a piece of kit that would significantly increase the volume? Preferably something that would simply plug in to the current set up. Thanks.
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Old 04-04-2013, 04:29 AM   #7386
Emoto
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Quote:
Originally Posted by Hayastani View Post
The audio output from my Montana 600, via an Autocom system, is barely audible at anything above approximately 40mph. I have adjusted the earpieces to the optimum position, the Autocom is at its highest setting as is the volume control on the Montana. Does anyone know of a piece of kit that would significantly increase the volume? Preferably something that would simply plug in to the current set up. Thanks.
I like and use the MixIt2 as an inline audio amplifier. My GPS, V-1, and iPod all feed into it, then to a Chatterbox GMRS X-1 and its headset. I don't have an autocom system, so am not sure how those are wired, but if you make this the last thing before the headset, it should give a nice boost to the sound level. The guy who owns the company is a rider and a good guy. http://www.mixitproducts.com/
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Old 04-04-2013, 09:45 AM   #7387
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Quote:
Originally Posted by dvmvm View Post
Its even simpler to test (fw 4.70):
  • Go to the tripcomputer and select the two data fields "elevation" and "GPS elevation". Switch autocalibration off.
  • With Setup - Altimeter - Barometer Mode = "Variable Elevation" the "elevation" data field uses the barometric sensor. You can press with your finger on the 4 little holes on the back of the Montana. You will see that the elevation datafield changes while pressing the holes firmly or softly, indicating that the "elevation" data field uses the baromatric sensor.
  • With Setup - Altimeter - Barometer Mode = "Fixed Elevation" you will see that the "elevation" and "GPS elevation" data fields are identical. Pressing the 4 holes does not change anything.

Anyway, I see no reason why this contradicts your findings for the barometric readings. I think the behavior for barometric reading and the one for elevation can co-exist.

Simpler for you - I don't have a Montana! I'm considering one so that's why I'm asking. According to Garmin's very thorough and concise manual the only data fields (appendix) for elevation are "elevation", "elevation maximum" and "elevation minimum" - they don't show one for "GPS elevation". Since the manual shows options that are pretty much the same as the 76Csx I was guessing that it would behave the same and the 76Csx will only show the GPS elevation on the satellite page by pressing "menu" and selecting "GPS elevation". It does not log GPS elevation or display GPS elevation in a data field no matter how the barometer is setup. Oh well....
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Old 04-04-2013, 10:47 AM   #7388
DRTBYK
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Quote:
Originally Posted by SteveAZ View Post
Simpler for you - I don't have a Montana! I'm considering one so that's why I'm asking. According to Garmin's very thorough and concise manual the only data fields (appendix) for elevation are "elevation", "elevation maximum" and "elevation minimum" - they don't show one for "GPS elevation". Since the manual shows options that are pretty much the same as the 76Csx I was guessing that it would behave the same and the 76Csx will only show the GPS elevation on the satellite page by pressing "menu" and selecting "GPS elevation". It does not log GPS elevation or display GPS elevation in a data field no matter how the barometer is setup. Oh well....
The "manual's", as all Garmin customers know by now, are incomplete and out of date the day they are released/updated.

What Garmin was doing was publishing on their Trail Tech website significant (my words) additions to the software. See the link at the bottom of the Need for Speed page for the link to the configurable data fields. I also believe that atlas cache has this info on his Wiki.

Check it out once and a while to see if they have made any updates.

Cheers,
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Old 04-04-2013, 02:46 PM   #7389
SteveAZ
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Quote:
Originally Posted by DRTBYK View Post
The "manual's", as all Garmin customers know by now, are incomplete and out of date the day they are released/updated.

What Garmin was doing was publishing on their Trail Tech website significant (my words) additions to the software. See the link at the bottom of the Need for Speed page for the link to the configurable data fields. I also believe that atlas cache has this info on his Wiki.

Check it out once and a while to see if they have made any updates.

Cheers,
Good stuff. Nice to know they will display GPS elevation. I'm still skeptical about logging it but maybe I'll just break down and get one anyway...
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Old 04-04-2013, 02:55 PM   #7390
DRTBYK
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Good stuff. Nice to know they will display GPS elevation. I'm still skeptical about logging it but maybe I'll just break down and get one anyway...
If you want to "log" the elevation just turn the track-log on. The GPS elevation is recorded with each track point.

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Old 04-04-2013, 03:33 PM   #7391
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What's up with this?

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Old 04-04-2013, 04:30 PM   #7392
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"Date First Available April 1, 2013"

"Item weight 1.5 pounds"

"Shipping weight 1 pounds"

Sounds fairly obvious to me.
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Emmbeedee screwed with this post 04-04-2013 at 04:50 PM
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Old 04-04-2013, 05:07 PM   #7393
dvmvm
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Quote:
Originally Posted by SteveAZ
...I'm still skeptical about logging...

Here is an example from the 62ST from the dutch forum: http://forum.gps.nl/viewtopic.php?f=...art=60#p315994
Lex logged both the GPS-elevation and another time the barometric elevation and compared these with mapping data.
It is known that the firmware of 62ST and Montana are almost alike and updated within short periods of each other.
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Old 04-04-2013, 05:32 PM   #7394
SteveAZ
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Quote:
Originally Posted by DRTBYK View Post
If you want to "log" the elevation just turn the track-log on. The GPS elevation is recorded with each track point.

Cheers,
GPS receiver elevation not "corrected" by the pressure sensor or the sensor "corrected" elevation? Like I've mentioned, the 76Cs(x) will only record the "corrected" elevation not the GPS receiver only data regardless of the barometer settings in the unit.
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Old 04-04-2013, 05:36 PM   #7395
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Quote:
Originally Posted by dvmvm View Post

Here is an example from the 62ST from the dutch forum: http://forum.gps.nl/viewtopic.php?f=...art=60#p315994
Lex logged both the GPS-elevation and another time the barometric elevation and compared these with mapping data.
It is known that the firmware of 62ST and Montana are almost alike and updated within short periods of each other.
Well my dutch wasn't good enough to understand the plots and I doubt they would answer my question regardless.

As I mentioned one the easiest tests for this is to take the unit up in a commercial aircraft and see whether the track log elevation maxes out at 7.5-8.5K' instead of 30-40K'....
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