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Thread: Altitude Readings - GPS or Altimeter (barometer) ?

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    Luckily the indicated Altitude inside my Keg is sub zero so I can elevate myself a nice cold one
    This era of thoughtless consumption must end so we can encourage a world of creative geniuses rather than consumer idiots.


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    Quote Originally Posted by Thala Dan View Post

    "Crazy location"....how do you define that?
    ok so you stub your toe and need rescuing in the mountains so mr westpack helicopter comes and picks you up and you get a 2 minute joy ride to hospital.

    crazy location as follows.
    Alice springs to halls creek via tanami rd.
    if you screw up here it takes at least 5 hours for someone to get to you IF you are super lucky the RFDS can land on the road if not one of the mines sends out a car to scrape you up and take you back to the mine then you get to go on the RFDS.

    birdsville track is going to have to be renamed to birdsville road it is going blacktop.

    Alice springs to finke.
    has about 25 houses.
    watching millions of dollars worth of cars go screaming past is great.

    things you need out there.
    iridium sat phone.
    more than 40l of water.
    40+l fridge full of coldies.
    spare cartons to keep fridge full.
    spare battery
    solar panel
    uhf handheld mounting radio in car sounds great until you need to climb sand dune.
    spare diesel.
    spare tire X2+ tire plug kit air compressor.
    at least one other 4WD'er to travel with.
    that would be the basic stuff but i take so much more.

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    Quote Originally Posted by eeprommemory View Post
    things you need out there.
    iridium sat phone.
    more than 40l of water.
    40+l fridge full of coldies.
    spare cartons to keep fridge full.
    spare battery
    solar panel
    uhf handheld mounting radio in car sounds great until you need to climb sand dune.
    spare diesel.
    spare tire X2+ tire plug kit air compressor.
    at least one other 4WD'er to travel with.
    that would be the basic stuff but i take so much more.
    No Spot 3 GPS beacon or HF Radio?
    I watched as 2 mates had complete fails with their Sat Phones on the Simpson
    I was pretty keen to get one before this

    Anyway, this is digressing from the topic i guess.
    If u want to go on an expedition get a Land Rover, if u want to come home from an expedition get a Landcruiser!

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    Quote Originally Posted by ol' boy View Post
    No Spot 3 GPS beacon or HF Radio?
    I watched as 2 mates had complete fails with their Sat Phones on the Simpson
    I was pretty keen to get one before this

    Anyway, this is digressing from the topic i guess.
    A bit tangential perhaps, OB...but not irrelevant.
    Your original query about taking spot fixes of altitude evolved into the use of smartphones and their integral GPS/maps/apps to find your way around the high country.
    That then evolved into a conversation about reliance on smartphones in that alpine environment......at least from my perspective, it did.

    Everything I said in my posts 22, 42, 62, 77, and 86 related specifically to the alpine environment.....but somehow we keep moving out to somewhere into the middle of the Simpson desert.


    Seems to me that the comment:

    ok so you stub your toe and need rescuing in the mountains so mr westpack helicopter comes and picks you up and you get a 2 minute joy ride to hospital.
    indicates that a meeting of the minds is not going to happen here, so I'll just leave it at that.

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    Quote Originally Posted by eeprommemory View Post
    ok so you stub your toe and need rescuing in the mountains so mr westpack helicopter comes and picks you up and you get a 2 minute joy ride to hospital.

    crazy location as follows.
    Alice springs to halls creek via tanami rd.
    if you screw up here it takes at least 5 hours for someone to get to you IF you are super lucky the RFDS can land on the road if not one of the mines sends out a car to scrape you up and take you back to the mine then you get to go on the RFDS.

    birdsville track is going to have to be renamed to birdsville road it is going blacktop.

    Alice springs to finke.
    has about 25 houses.
    watching millions of dollars worth of cars go screaming past is great.

    things you need out there.
    iridium sat phone.
    more than 40l of water.
    40+l fridge full of coldies.
    spare cartons to keep fridge full.
    spare battery
    solar panel
    uhf handheld mounting radio in car sounds great until you need to climb sand dune.
    spare diesel.
    spare tire X2+ tire plug kit air compressor.
    at least one other 4WD'er to travel with.
    that would be the basic stuff but i take so much more.
    Thanks, eprom........you clearly have a great deal of experience travelling the inland.

    My interest in this discussion has centred solely around the use of smartphones as primary navigation and safety devices in the alpine environment.........an environment in which you don't appear to have quite as much experience.

    This is an article you might find interesting.....not exclusively about the Snowies....but indicative of the problems faced trying to find somebody when the surrounding countryside is not as flat as the proverbial.

    When you combine rugged bush terrain with freezing temperatures, snow, and high winds things get a bit awkward.

    How does a bushwalker go missing, never to be found?

    Klaus Hueneke, renowned for his books and photographs of the Australian Alps, led a successful search in 1988 to rediscover the site where Hayes' body had been found. I ask him about the Srawn case. He explains: "Finding a cairn or a body in that landscape is like finding a contact lens on the bottom of a swimming pool. Between Mount Townsend [where Srawn's last mobile transmission came from] and the Alpine Way is one of the most rugged valleys in Australia. It's cold, wet, treacherously steep, full of fallen trees, difficult rivers to cross, almost as tough as temperate rainforest in Tasmania. His body may never be found, irrespective of the size of the reward. I don't think he wanted to vanish, but if he did it was a good place to do it."

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    What i can see from this thread, is both your devices Thala are pretty dam close to each other!
    Close enough for my needs i'd suspect.

    Amazing considering one as GPS only and the other is Barometric only
    (I hope that is correct?)

    So many people telling me how i need to calibrate the Barometric device, sometimes 3 times a day from known datum points
    Yet, i'm sure you didn't do this?

    Would be great if next time you go into the mountains Thala, you take them and can redo the test at a higher elevation (see, i used my correct words)
    In the mean time, i still have no answers for one question:

    If a device has GPS and Barometer, which does it use for the displayed reading?

    Perhaps the one that gives the most stable result??
    In the case of the App that eeprommemory linked, i guess it was the Barometer first, then GPS as a fall back|
    As App displayed a "pop up" saying no "Barometer on this device" when it first opened after downloading, and just uses GPS ever since
    (It does not show the pop up about "No Barometer" on subsequent uses of the App)

    This a another reading from my house (taken right now), exact same location as the previous
    Previous readings using the Redmi (GPS only) were 61m and 71m.

    Last edited by ol' boy; 14-08-19 at 11:14 AM.
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    Quote Originally Posted by ol' boy View Post
    In the mean time, i still have no answers for one question:

    If a device has GPS and Barometer, which does it use for the displayed reading?
    Depends on the device I believe, some allow use of barometric only, some are like my watch where you have the option of either, and others, particularly older devices, use GPS only.

    Quote Originally Posted by ol' boy View Post
    This a another reading from my house (taken right now), exact same location as the previous
    Previous readings using the Redmi (GPS only) were 61m and 71m.
    can be a cause of varying readings, if a device is accurate to say 5 metres for example, that 5 metres can be horizontal or vertical.
    And there's many other factors that can affect readings/accuracy.
    I'm finding with newer devices enabling both GPS & in the Satellite settings improves accuracy.

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    Quote Originally Posted by ol' boy View Post
    What i can see from this thread, is both your devices Thala are pretty dam close to each other!
    Close enough for my needs i'd suspect.

    Amazing considering one as GPS only and the other is Barometric only
    (I hope that is correct?)

    So many people telling me how i need to calibrate the Barometric device, sometimes 3 times a day from known datum points
    Yet, i'm sure you didn't do this?

    Would be great if next time you go into the mountains Thala, you take them and can redo the test at a higher elevation (see, i used my correct words)
    In the mean time, i still have no answers for one question:

    If a device has GPS and Barometer, which does it use for the displayed reading?

    Perhaps the one that gives the most stable result??
    In the case of the App that eeprommemory linked, i guess it was the Barometer first, then GPS as a fall back|
    As App displayed a "pop up" saying no "Barometer on this device" when it first opened after downloading, and just uses GPS ever since
    (It does not show the pop up about "No Barometer" on subsequent uses of the App)

    This a another reading from my house (taken right now), exact same location as the previous
    Previous readings using the Redmi (GPS only) were 61m and 71m.
    Yes, OB - the Oregon is a barometric altimeter, and the eTrex is GPS-only.

    No - I haven't calibrated the Oregon since I bought it in July 2017.......It's been out fishing with me many times in the mountains as I've got Australian Topo maps V5 in it, and it gives me a good idea of the surrounding topography and shows all the little tributaries that might be worth exploring. I keep the barometric pressure on the main screen 'cause that gives me an idea if the wx is about to crap out - but this is the first time I've even bothered looking at the Elevation.

    I just took the Oregon out onto the verandah again - after a few seconds of stabilisation it is showing Elevation: 261m Barometer: 996.4

    So, both readings are on a par with those taken yesterday....at least repeatability is good

    Here's Garmins take on the subject of calibration:

    Barometric Altimeter Accuracy of Compatible Outdoor Devices
    With proper calibration, barometric altimeters will report elevations ranging from -2,000 to 30,000 feet within +/- 50 feet. The barometric altimeter may calculate values beyond 30,000 feet, but these values may not be accurate.

    Calibrated altitude maintains its accuracy as long as there are no significant changes in air pressure. Changes in weather are the most significant cause of changes in air pressure, but change in location can also affect the accuracy of the sensor, as air pressure can vary from location to location. Air pressure can also change when moving from indoors to outdoor, or outdoors to indoors or when a button is pressed1.

    Calibrating the sensor periodically will ensure the highest level of accuracy.

    Proper Calibration
    For an outdoor device to be properly calibrated:

    Calibration must be done outdoors
    Calibration may be done to a known elevation; calibration by GPS2 cannot guarantee accuracy within +/-50 feet
    If calibrating barometric pressure, the current barometric pressure for your location must be entered
    Refer to your Owner's Manual for instructions on calibrating the altimeter.

    Note: Garmin's outdoor devices are designed as recreational GPS devices, as an aid to navigation. They should not be used for any activity requiring precise measurements, such as surveying or weather prediction.

    1 When a button is pressed, the altimeter will lock for three seconds

    2 Calibration by GPS is accurate to +/-400 feet.
    I'll be heading up to Bright on Friday and will probably have an hour to kill - if so, I'll take both units on to Harrietville (elevation 510m), and might even get a chance to push a little further up the Alpine road toward Hotham. I won't do any prior calibration on the Oregon......just see what it says when I get there, and see what it says when I get back home.

    That's quite a swing from 61m to 89m - Edit: Just realised it was a GPS reading - not barometric which my earlier comment applied to. I think jma's comment is more on the money.
    Last edited by Thala Dan; 14-08-19 at 01:31 PM.

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    Quote Originally Posted by Jma View Post
    I'm finding with newer devices enabling both GPS & in the Satellite settings improves accuracy.
    Both my Garmins have GLONASS but I've never used it....primarily because I've seen so many comments about increased battery drain - must give it a go one day.

    Do you think it makes that much of a difference to battery life?

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    OB,

    Was going to write more, but was threatened with major anatomy rearrangement if I didn't get to lunch.

    I'll see what other opportunities arise for in-field tests, but come September 6 (Trout opening) I'll be heading up top regularly (wx permitting), so will then have exposure to much higher elevations.....keep you posted.

    It's about time I learned more about the capabilities of all this trinketry I carry around with me.

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    All in all, its pretty amazing for Free Service!
    Last edited by ol' boy; 14-08-19 at 04:01 PM.
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    Quote Originally Posted by Thala Dan View Post
    Both my Garmins have GLONASS but I've never used it....primarily because I've seen so many comments about increased battery drain - must give it a go one day.

    Do you think it makes that much of a difference to battery life?
    I'm not sure, I've never done any comparisons on battery only usage.
    I imagine using both GPS & GLONASS the battery usage would be heavier because of extra processing power etc. required.
    All I've done until now is try with and without GLONASS enabled for accuracy purposes, and my very unscientific testing proves they're more accurate with GLONASS enabled

    I have a Montana 610 and a GPSMap 276CX that are both GPS & GLONASS compatible, as well as the that's GPS, GLONASS & Galileo compatible, but it's limited to either GPS & GLONASS or GPS & Galileo or GPS only, can't use all 3 at the same time.
    It gets around 10-12 hours before the battery starts to get low on GPS only navigating, haven't tried it with the others.
    With the GPS off it lasts for weeks before needing a charge.

    I've used the Montana a few times with battery only & it's a real hog if you need the screen sunlight viewable all the time, about an hour tops before it shuts itself down using the Garmin battery, haven't tried it with AA's yet.
    Haven't used the 276 on battery apart from the initial setup when I first got it a few weeks ago, I imagine with the larger screen it might be similar to the Montana & eat batteries quick unless it's set to dim the screen & backlight etc. to preserve battery life.

    I also have a couple of the older GPS 60's, the original yellow ones, they have a battery saver mode for the GPS, whatever that does ( I think reduces the amount of communication with the satellites) allows them to be used for around 2 full days on a single set of AA batteries so long as the backlight is disabled, monochrome screen uses a lot less power than the coloured screens of the 610 & 276 which I imagine also has a lot to do with it.
    If I don't completely forget about it, one day I might have a play with them on battery only & time how they go with & without GLONASS.

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    Yes, apparently battery usage rate goes up with dual systems....even Garmin admit it:

    Features that Affect Battery Life on Outdoor Handheld

    GNSS (Global Navigation Satellite Systems): If the handheld supports the use of multiple satellite systems, such as GPS+GLONASS or GPS+Galileo, this can reduce the overall battery life when compared to using just GPS. GPS+GLONASS or GPS+Galileo does offer increased performance in challenging environments and faster position acquisition.


    If you decide to try some AA's in your Montana, I can recommend the Panasonic Eneloop Pro.....I use them in the Oregon 600, among other things.

    Garmin-supplied batteries don't exactly have a big fan club.

    Have bought off this bloke......reasonably fresh stock and good price:



    But you're right....those colour screens, nice as they are, eat batteries for breakfast.

    Must have a look at that GLONASS stuff.......used in conjunction with GPS, might just provide some decent elevation outputs, which is where this thread all started.

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    They're damn good batteries those Eneloop, I've been using nothing but now for many years in the GPS60, cameras, remotes etc..
    Thanks for the link to that seller, I've had the occasional dud from various places over the years, probably old stock I guess.

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    here is what the app looks like if you have a barometer.

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    Quote Originally Posted by ol' boy View Post
    No Spot 3 GPS beacon or HF Radio?
    I watched as 2 mates had complete fails with their Sat Phones on the Simpson
    I was pretty keen to get one before this

    Anyway, this is digressing from the topic i guess.
    have HF don't use it.
    sat phone fail sounds like user error.

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    Quote Originally Posted by eeprommemory View Post
    sat phone fail sounds like user error.
    2 Sat Phones, 2 Vehicles, 2 People
    Both Inmarsat phones

    One Failed to even turn on, even though it was showing fully charged while travelling in vehicle
    The other turned on, but all 3 vouchers failed to work, they were tested prior to leaving.
    But you are correct, it was user error in the end for the "working" phone and they eventually got the voucher working.

    Can you call 000 from a Sat Phone with no credit or account?

    Last edited by ol' boy; 15-08-19 at 10:23 AM.
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    Some interesting results today
    Dr Karl will be happy i've done the test

    My friend over the range has a phone with barometer (and GPS), using the same App that eeprommemory linked we found, to our amazement, that our homes were around the same elevation, 65m-70m or there abouts. Him using Barometer, me using GPS.

    Today, i asked him to recheck his elevation, wow, it said 129m using Barometric
    He has also checked on other mornings and its all been give or take around the 65-75m mark.

    Exact same location, using a Google Pixel 2


    Tuesday



    Thursday (today)




    Now, we are at the end of a High Pressure system with North winds and there is a cold front approaching
    I am guessing this is why his Barometric elevation reading has really moved about???






    Question, what are the 2 barometric pressure readings mean either side of the height?
    Or why is there 2?
    Last edited by ol' boy; 15-08-19 at 12:37 PM.
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    Quote Originally Posted by ol' boy View Post

    If a device has GPS and Barometer, which does it use for the displayed reading?
    Answered my own question in relation the App that eepromemory linked
    It will prefer Barometer, but it is selectable



    And can be calibrated




    App Details

    Here are the main features :

    - 3 hands analog altimeter (Hundreds, thousands & tens of thousands).
    - Sensor "Autostart" feature (see preferences).
    - Automatic sensor stop on exit.
    - Preferences save on exit (including calibration data).
    - 2 altitudes providers : Barometric sensor(*) or GPS chip (no network).
    - Robust Barometric Algorithm.
    - Units are feet or meters for altitude and hPa or inHg for pressure (*).
    - Displays QFE / Altitude / QNH (*).
    - Altitude speech.
    - Calibration function(*) with altitude or pressure (QNH) including a reset function.
    - User interface in English, French, German (Thanks Peter), Italian (Thanks Cosimo !).
    - Free application... no ad !

    (*) These functions require a barometric sensor in your android device (tablet like Motorola Xoom, Google Nexus ics 4, Samsung Note, ...).


    By default the program will attempt to start with the pressure sensor. If it is not found then it switch on the GPS provider (true GPS not the network GPS). A message is displayed if the pressure sensor is not found.

    Please note also that the program doesn't use Internet to get the altitude. For that reason, the program when used with GPS won't run indoor !

    The GPS, was implemented to overcome the lack of pressure sensor on most devices.

    The pressure sensor is very accurate : with a resolution of 0.1hPa and after calibration, accuracy is about 1m. This is awesome !

    More into:
    Last edited by ol' boy; 15-08-19 at 12:28 PM.
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    Interesting Reference:



    If u want to go on an expedition get a Land Rover, if u want to come home from an expedition get a Landcruiser!

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