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  1. #1
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    Garmin Edge 500 elevation

    Just got back from a ride from my house to the beach
    after down loading the info onto garmin connect have found that the the edge was showing me 10 to 15 meters below sea level when i was closest to the beach
    My destination was at the top of a hill yet it still showed me below sea level

    Did i miss a step in setting it up or is there another reason for it to show me below when there is no way i would be riding my new bike in the Salty water of the bay


    Twiggy73

  2. #2
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    THe first time you use an Edge you need to give it time to "find itself". So switch it on and put it on a flat surface with clear sight of the sky and leave it until the elevation settles. Once it knows where it is using the satellites the altitude will be set up. The altimeter only used the barometric feature to determine change in altitude.

  3. #3
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    Quote Originally Posted by ultimobici
    THe first time you use an Edge you need to give it time to "find itself". So switch it on and put it on a flat surface with clear sight of the sky and leave it until the elevation settles. Once it knows where it is using the satellites the altitude will be set up. The altimeter only used the barometric feature to determine change in altitude.
    Have Done this and it still had me at -27meters below seal level when i was at sea level ??? ( I checked the route again last night)

    It had me at -10 when i was at about +50 could weather conditions effect the readings

    It was dry and warm at teh time of the ride

    Thanks

    Twiggy

  4. #4
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    I admittedly don't have the 500 yet....still have the 301...I was under the impression that altitude function on the 500 wasn't GPS based but was based on barometric pressure.

    I could be wrong...it wouldn't be a first.
    "Indecision may or may not be my problem."

  5. #5
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    Quote Originally Posted by twiggy73
    Have Done this and it still had me at -27meters below seal level when i was at sea level ??? ( I checked the route again last night)

    It had me at -10 when i was at about +50 could weather conditions effect the readings

    It was dry and warm at teh time of the ride

    Thanks

    Twiggy
    Try hard resetting the unit then seeing if it will find the right altitude. Also make sure that you have updated the software. Even a new straight out of the box unit needs updating as there may have been updates since it was produced.

  6. #6
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    My Dad is looking into the Garmin 500, and this has confused me. Why does it need the barometric sensor? Why can't it get accurate elevation data from the GPS? I'm new to the GPS thing so it might be a simple answer.

  7. #7
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    Quote Originally Posted by twiggy73
    Have Done this and it still had me at -27meters below seal level when i was at sea level ??? ( I checked the route again last night)

    It had me at -10 when i was at about +50 could weather conditions effect the readings

    It was dry and warm at teh time of the ride

    Thanks

    Twiggy
    The way the Garmins work is as follows: In an initializion phase it determines your absolute altitude from GPS. This happens to be the critical step: GPS accuracy for the vertical coordinate (altitude) is always much lower than for the horizontal coordinates, by a factor of 3 at least, in my experience. There are fundamental mathematical reasons why this has to be so. Thus, if your position is accurate to within 5 meters, say, expect errors in altitude of at least 15 meters. After that initial calibration (which happens when you turn on the unit and it locks on to satellites), the unit will use a barometric altimeter to determine your changes in altitude. It turns out that this method is in fact more accurate than the GPS data, but only as long as the barometric pressure remains about constant. So, if there is a thunderstorm moving in while you're riding, the associated pressure front will show itself as a spurious change in altitude. In summary, you cannot put too much trust in the altitude data from any of the existing consumer units.

    One alternative for more accurate data is to use SportTracks, a far more powerful alternative to Garmin's Training Center software. It has an optional altitude correction function built in that fetches your elevation based on your horizontal coordinates from publically available elevation data.

  8. #8
    but thinking about it
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    Quote Originally Posted by Pirx
    The way the Garmins work is as follows: In an initializion phase it determines your absolute altitude from GPS. This happens to be the critical step: GPS accuracy for the vertical coordinate (altitude) is always much lower than for the horizontal coordinate, by a factor of 3 at least, in my experience. Thus, if your position is accurate to within 5 meters, say, expect errors in altitude of at least 15 meters. After that initial calibration (which happens when you turn on the unit and it locks on to satellites), the unit will use a barometric altimeter to determine your changes in altitude. It turns out that this method is in fact more accurate than the GPS data, but only as long as the barometric pressure remains about constant.
    If you set a number of known elevations (Menu/GPS/Elevation Points) for points that you often ride through, you can greatly reduce the impact of changing pressure along your "usual" routes.

  9. #9
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    Quote Originally Posted by Undecided
    If you set a number of known elevations (Menu/GPS/Elevation Points) for points that you often ride through, you can greatly reduce the impact of changing pressure along your "usual" routes.
    Hmm, interesting! My Edge 705 doesn't have that function. Of course, in general the question still is, how do you determine the elevation you are supposed to put in? That would not be that much of a problem for the sea level situation (in many locations, anyway), but otherwise you need to find a point that has an elevation marker.

  10. #10
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    Doesn't Google Earth have an altitude feature that could be used as a benchmark for setting up a GPS?
    Michael - There may not be an 'I' in team but there is a 'U' in suck!
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  11. #11
    but thinking about it
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    Quote Originally Posted by Pirx
    Hmm, interesting! My Edge 705 doesn't have that function. Of course, in general the question still is, how do you determine the elevation you are supposed to put in? That would not be that much of a problem for the sea level situation (in many locations, anyway), but otherwise you need to find a point that has an elevation marker.
    I use Google Earth, actually.

  12. #12
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    Setup your trainer in the driveway, boot your Garmin, ride for an hour, and though you haven't gone anywhere, you will have climbed or descended with the fluctuations in barometric pressure. Altimeters in airliners, that are much better than the itty bitty one in the Garmin, can still be off up to 75 feet on the ground at a known elevation, and that's allowing for setting the correct barometric pressure. The differences between two altimeters can be even greater at higher altitudes and be perfectly acceptable. I'd imagine + or - 15 meters would be acceptable for your bicycle.

  13. #13
    So. Calif.
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    The barometric altitude sensor in the Garmins must have some kind of air temperature-density correction, even if it isnt accessible or visble to the user.

    I've noticed when my Garmin 305 has been stored indoors (warm) and I take it out on a (colder) morning ride, it will read my altitude from 50-100 feet lower than actual (cold air = denser air -> thinks it's lower elevation).

    The Garmin 305 takes about 20-30 minute to equilibrate to significantly different (20) temperatures.

    If altitude accuracy at the beginning of a ride is critical, store the Garmin at similar temperatures expected during the ride ... eg, in the garage if you're riding first thing in the AM.

  14. #14
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    Thanks for all the replies will look at reseting the gps
    I have looked up our elevation and will compare it to the garmin and I will also give that other sports track software ago to
    And will get back on my results

    Thanks
    Twiggy73

  15. #15
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    I just got a Garmin 500 about a month ago 08/18/12. I did the so called setup by going outside to find the elevation of my house.
    BUT, when you are at a starting point someplace else, that initial elevation point does not work for where you are.
    I rebooted, like Garmin told me to (I did). I made sure the firmware was current (it was).
    I would do a ride of about 63 miles and got over 800 feet incorrect from what other's were getting on their 705. I got about 900 feet wrong on the Garmin when I compared it to my Bontrager Node 1.1.
    My Bontrager Node 1.1 was about 100 feet off....... Much better then the Garmin.

    When you say initial setup, are you saying once the computer gets turned on (out of the box), OR are you saying each time you are at a starting point to do a ride, you turn it on and wait for it to receive a signal ?

    I thought that when you are at a starting point, (someplace besides your home). You turn on the Garmin, and wait for it to find the satellite. Watching the bar go to full, then seeing your first page.

    Needless to say, the 500 is going back since it's not reliable. I did order another one, just to make sure.

  16. #16
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    Quote Originally Posted by twiggy73 View Post
    Just got back from a ride from my house to the beach
    after down loading the info onto garmin connect have found that the the edge was showing me 10 to 15 meters below sea level when i was closest to the beach
    My destination was at the top of a hill yet it still showed me below sea level

    Did i miss a step in setting it up or is there another reason for it to show me below when there is no way i would be riding my new bike in the Salty water of the bay


    Twiggy73
    Set an elevation point. Go to a GPS survey site and get the exact mean sea level elevation for that exact location (mine is home; lat/long); then set elevation for that known point in your Edge. Previous poster mentioned: MENU/GPS/Elev point

  17. #17
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    Quote Originally Posted by robpar View Post
    Set an elevation point. Go to a GPS survey site and get the exact mean sea level elevation for that exact location (mine is home; lat/long); then set elevation for that known point in your Edge. Previous poster mentioned: MENU/GPS/Elev point
    This works well if you do it for the START of your ride. If you do it like 30 mi in at a point, the Garmin will adj to that as the altitude and throw off your total a lot.

    One time my Garmin 800 gave me 1400 ft of climbing in 0.2 miles. Why? because I had set a waypoint with altitude near the begining of my ride. It's intial estimate by barometer was rather off.
    It's a fire road.............
    I'm on a road bike..........

    They have enough in common to blast down it.

  18. #18
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    Quote Originally Posted by ziscwg View Post
    This works well if you do it for the START of your ride. If you do it like 30 mi in at a point, the Garmin will adj to that as the altitude and throw off your total a lot.
    So are you saying you shouldn't set known altitude points for various places that you frequently ride through, like Undecided suggests above?

  19. #19
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    Forget it

    In order to receive accurate elevations on your Garmin you need to have a base station relaying data from a known point. Surveyors use this method with their $40,000 units. The base station relays corrected data to their mobile unit via radio waves. The best you can hope to achieve with your 500 model is 5 to 10 meters vertically.

  20. #20
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    Supposedly the Garmins will adjust their elevation if left in one spot after being turned on. But I never want to wait that long, and I think I tried it when the 705 was new, and it didn't seem to change much.

    The 705 has "Save Location" on it's main menu. Select it then select Avg at the bottom of the screen. It makes continuous satellite readings, and eventually the displayed elevation converges to the actual correct value. I usually let it sit for 60 seconds or more, and whenever I've done this at known elevation points, it's been pretty accurate, within 10 feet or less. Click OK to save this elevation point.

    Then, when you start a ride within 100 feet of this point, it'll say "elevation point found" and immediately sets the starting elevation correctly. (Nothing happens until you hit Start.) Unfortunately, it ignores other known elevation points when riding.

    I gained 200 feet once during a 10 minute break at a rest stop when a summer storm passed by and the air pressure dropped.

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Adjusting elevations from mapping sites:

    ridewithgps offers to adjust my elevations using their own elevation maps. I never do this, since mapping sites have their own inaccuracies.

    For instance, the exact elevation of a road surface on the side of a hill has to be estimated by using known elevations nearby. This can show some incorrect grades when the road height is too high or low.

    Here's an example from the excellent, free "My Tourbook" software. It uses SRTM elevation data from NASA to propose adjusting my green elevation data to the red line. You can see that it's much more jagged and therefor will show more total elevation gain for the ride. The green line from 705 barometer data is much better--this is the Blue Ridge Parkway, and it's a smooth, steady grade on these climbs.

    They also sometimes don't know that a bridge crosses a ravine, thinking the road has to plunge down to the bottom and back up the other side. Or the elevation goes over the top of a ridge above a tunnel.

    Still, the differences are mostly less than 50 feet. It's pretty amazing that an extremely small barometer built into a GPS unit could be this accurate.

    Normally, the mapping site elevation adjustments are used to correct GPS recordings that didn't have a barometer, since those can be pretty inaccurate.

    Last edited by rm -rf; 09-18-2012 at 03:41 PM.

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