Announcement

Collapse
No announcement yet.

Barometer/Altitude issues

Collapse
X
  • Time
  • Show
Clear All
new posts

  • #46
    Originally posted by MATTHEW2811 View Post
    The first attachment shows the run WITH elevation correction switched on in Garmin Connect which I understand to mean GPS data is being used.
    Elevation correction means that Garmin Connect uses a digital terrain map (there are different versions available) to look up the elevation at each lat-long point that you recorded. The old MB used to do this, and it provided a good correction since early Forerunner devices used GPS to determine altitude, which is not a very accurate method, especially if you are moving.

    Comment


    • #47
      Thanks Luca, DW.
      Interesting, looks like I completely misunderstood the data sources for elevation calculation. Perhaps my post title should now read, 'professional survey/digital terrain mapping 1 - watch elevation/altimeter 0'. Luckily this isn't a feature that was a principal buying point for me, other than having it will be useful for finding out the gradient of hills I ride or run on. I'll just wait for the firmware update like everybody else.
      It does seem quite a fundamental problem though in a brand new product as my watch generated data in attachment two bears no resemblance what-so-ever to that in attachment one.
      Last edited by matthew2811; 01-31-2012, 12:46 PM. Reason: spelling

      Comment


      • #48
        takes about 90 seconds to figure out elevation, plus some more research

        For the second run in a row, I started at about 700' elevation, then after 60-90 seconds popped up to the correct elevation of 900-1000 feet. Makes for some generous (incorrect) reads. Something is definitely up with that, at a minimum. That 60-90 seconds is all AFTER the GPS locks on. Below is a post I made on slowtwitch a few days ago after researching where the elevation correction data comes from. For me, I concluded I'm pretty happy with that most of the time. I could see how you hikers and more rural dwellers might feel differently:


        Re: Garmin/GPS elevation correction [perullo]
        I think I found the answers.
        Short story: the elevation correction in garmin connect is accurate to at least 10 meters (it knows the elevation of a coordinate every 10 meters) over all of the US. It is accurate to 3 meters for certain areas - usually LIDAR mapped. This isn't 10/3 meters of up/down. Rather, it means that every 10/3 meters you run, you hit a spot where it has a very accurate gauge of the elevation. So if you took a smooth rise/fall between the two points, it is spot on. If you crested some magical 3-meter wide 100-foot tall spire, you are out of luck. All of the above are updated very frequently (monthly or better). If you approach a canyon on a bridge, you should run down the canyon wall and up the other side to make sure your data is good. If you take the bridge you are on your own.
        The last release notes for the data set including a map of resolution coverage is here: http://ned.usgs.gov/...ease_Notes_Dec11.pdf
        Sounds very accurate, and it looks like my city is LIDAR-mapped... just like ALL of west virginia.. for some reason.

        I would THINK this would be better than the barometer.

        Outside the US there are other sources with varying accuracy.. see below for more detail.

        My data came from this thread:
        https://forums.garmin.com/showthread...ght=topography
        LARRY_F_S
        Junior Member

        Join Date: Jan 2011
        Location: Fort Worth, TX
        Posts: 3

        Thanks for the info Peter. Here’s what I also learned after some correspondence with Garmin Support:
        1. The elevation corrections feature of Garmin Connect is set to Disabled for the 705 and 800 since they have their own altimeter. With Disabled, Garmin Connect uses the elevation data from the 705/800 altimeter.
        2. The 800 stores track points based on changes in speed and direction. Changes in elevation don’t generate track points.
        3. Changing elevation corrections to Enabled causes Garmin Connect to ignore the elevation data from the 705/800 and use data from professional surveys. More specifically, the following is what a Garmin Product Support rep told me: “If you enable elevation corrections the website ignores all elevation data from the device and uses a combination of datasets to produce the best elevation corrections possible. Specifically, US coverage comes from the National Elevation Dataset from the USGS, Canada coverage comes from the Centre d'information topographique de Sherbrooke (CIT-S) dataset, and the rest of world data relies on data from the Shuttle Radar Topography Mission (SRTM) dataset from NASA. Elevation data outside of the US and Canadamay not be as accurate."
        For my last ride of 26 miles here in north Texas, my 800 displayed an elevation gain value of 1273 feet. After uploading my ride data to Garmin Connect, the elevation gain value was 1273 feet (corrections Disabled) as it should have been. I selected corrections Enabled and the elevation gain value changed to 837 feet. That’s a big difference and I’m not sure which one is more accurate. If I had the 705’s option to record track points 1/sec, I think I would tend to believe the corrections enabled value for it.
        The Garmin Product Support rep also commented on my which is more accurate question as follows: “Which is more accurate? That is a good question. Regardless of the device or method used it is important to realize these devices are consumer grade and can introduce a level of error that is not acceptable for survey level data. The Edge 800 is more likely to have more accurate elevation information than the Edge 705 so elevation corrections should be minor. Are the "elevation corrections" more accurate than the Edge 800? Using the auto-calibration feature on the device, the accuracy is +/- 50-125ft (same as GPS elevation). With WAAS and good reception you can obtain an accuracy of +/- 25-50ft. When manually calibrating to a known elevation it is approximately +/- 10ft for the first 15 minutes. Accuracy can change due to natural pressure changes (changes in weather). Potentially the information on our website may be more accurate as many things can effect the altimeter of your GPS. There is a limit however to this potential accuracy, as indicated on our website, "Elevation Corrections has known limitations for certain geographic features such as bridges and cross country borders where different elevation datasets prevail." So in summary, in certain circumstances the Edge 800 will be more accurate than Elevation Corrections (and usually more accurate than the Edge 705), but overall the Elevation Corrections may provide the additional accuracy you need. Regardless of your choice, please be aware these devices are consumer grade and only survey grade devices should be used if sub-meter accuracy is desired."

        Larry

        Comment


        • #49
          In cases where there's professional surveys being done on the terrain, I have reasons to believe it will be more accurate than the barometer's data. I think in Singapore, there's isn't any survey done. Places where I run where terrain is flat, I see some elevations. So in such instances, I do believe that the barometer might do a better job.
          A Bit of Swim, Bike and Run Blog - www.imdz.org

          Comment


          • #50
            If the terrain is hilly, you will be more accurate with the barometric pressure of the 800 (and hopefully the 910 some day). The problem is the GPS locations aren't accurate enough. There are places I run where you run along 1000' cliffs. If your GPS data points are off by 10', the "corrected" altitude based on surveys can be off by 1000'. While this is an extreme, running on hills in the trees, your GPS track can easily be off by 50' or more (even when it says you have 20' accuracy). The surveyed altitudes can be off significantly 50' to your right or left. Suddenly that nice smooth 5% grade turns into a bunch of small climbs and descents.

            Also as mentioned below, go across a bridge and the surveyed altitude will be at ground level, not bridge level.

            In relatively flat terrain, the "corrected" altitude will generally be more accurate.

            Comment


            • #51
              Test with and without elevation correction

              Hi, I'm based in Austria. Maybe elevation correction isn't that accurate here because US guys are not interested too much in our territory ;-). However, on a total flat running workout 136m gain with elevation correction and 70m gain without elevation correction is not what I expect from a watch with barometic systems. My Polar (RS800) show about 5-10m gain on the same track. This might be accurate, because there are some bridges and some small ups and downs. But 70m or even 136m is absolutely wrong. Hope Garmin will fix with a SW update soon the barometic system in 910xt. Elevation correction as I understood, is not in the control of garmin, so I can't blame them ;-). I will open a ticket as well.
              Attached Files
              Last edited by leebge; 02-05-2012, 05:44 AM.

              Comment


              • #52
                At this point, until we have a firmware update, I would put zero energy into analyzing the elevation and ascent information from the 910. It is completely useless at this point. Right now, using elevation correct is your better choice.

                The good news is it is so bad that Garmin has to make it a high priority. The bad news is they have taken months at times to get even more serious issues (like corrupt files) fixed. They should have had this fixed by now! No excuses! But I'd love to hear what their excuses are.

                Comment


                • #53
                  I now see an update on http://www8.garmin.com/support/fitne..._software.html !! I'm not at home to install yet and can't seem to find a changelog.

                  Comment


                  • #54
                    Originally posted by RTIMKO View Post
                    I now see an update on http://www8.garmin.com/support/fitne..._software.html !! I'm not at home to install yet and can't seem to find a changelog.
                    I don't see an update. If I follow the link, it says my device is up to date. Also, Garmin Connect doesn't indicate there is an update.

                    Comment


                    • #55
                      Originally posted by EKUTTER View Post
                      I don't see an update. If I follow the link, it says my device is up to date. Also, Garmin Connect doesn't indicate there is an update.
                      Yeah, the 910 wasn't listed there a few days ago, and then it was. That's what garmin support told me to look out for so I got excited when I saw the 910 listed...only to come home and be disapointed!

                      Comment


                      • #56
                        Holding Calibration when GPS disabled

                        Here's an interesting and slightly annoying pickup I just had. I just now turned my 910XT on and the barometric altimeter showed 52m. I then waited for it to find Sats and calibrate the altimeter, which it did pretty quickly and calibrated the altimeter to 113m which is about the correct number for where I am. Great.
                        I then went inside and manually disabled the GPS however the altimeter didn't hold the calibration but immediately reverted back to (the incorrect) 52m.
                        I guess it doesn't change the world but I would have assumed the calibration would be held in the unit until a newer calibration is available to reduce the size of the variation. e.g. 61m in this case. Anyone else seen this?

                        Comment


                        • #57
                          According to DC Rainmaker, Garmin will be releasing a firmware update in the next 7 days. He also mentioned that Garmin typically releases updates on Fridays. Let's hope that's the case!

                          After the release...I'm anxious to hear your results as I am stuck in "should I buy it or not?" mode until this altimeter issue is resolved.

                          Thanks.

                          Comment


                          • #58
                            Update on the GPS vs. Barometer

                            OK here's a short coffee break update. Just did the test a bit more scientifically and here's the result.

                            Firstly some times I recorded.
                            55s from turning the device on to Satellites acquired
                            2min20s later the altitude was re-calibrated.

                            So not so bad really. Just need to get the unit turned on at least 3mins before the activity starts for accurate start altitude and not just dash off as soon as GPS is found.

                            Following on from the previous post I then walked inside with the device and a minute or so later the warning popped up the GPS signal was lost. The important thing here is that the altitude calibration held firm through this which is good. Then I disabled the GPS and instantly the altitude calibration was lost. I can't think of a reason why this would logically be correct. Can Garmin confirm this fix is on the next firmware update or is it for later?

                            Comment


                            • #59
                              Originally posted by MESTEVIET View Post
                              According to DC Rainmaker, Garmin will be releasing a firmware update in the next 7 days. He also mentioned that Garmin typically releases updates on Fridays. Let's hope that's the case!

                              After the release...I'm anxious to hear your results as I am stuck in "should I buy it or not?" mode until this altimeter issue is resolved.

                              Thanks.
                              Hi Mesteviet, My Advice. Buy it. overall it's a great unit and these are all just teething issues. We are all perfectionists and want the absolute best from our devices so we complain (and help). I had the 310XT from new and whilst at the start there were a few bugs the improvements that came with firmware over the life of the device were terrific and I'm glad I didn't wait before buying it. I forecast the same for the 910XT. Garmin's approach seems to be different from other companies with the user being the Beta+ testers and driving the priorities for bug fix's and improvements. If this is by design, I don't know, but it is what it is.

                              Comment


                              • #60
                                Originally posted by PRIVATEER29 View Post
                                Hi Mesteviet, My Advice. Buy it. overall it's a great unit and these are all just teething issues. We are all perfectionists and want the absolute best from our devices so we complain (and help). I had the 310XT from new and whilst at the start there were a few bugs the improvements that came with firmware over the life of the device were terrific and I'm glad I didn't wait before buying it. I forecast the same for the 910XT. Garmin's approach seems to be different from other companies with the user being the Beta+ testers and driving the priorities for bug fix's and improvements. If this is by design, I don't know, but it is what it is.
                                Privateer29,

                                The main issue for me is the altimeter. The Suunto Ambit is coming out in late March and I want to get the most accurate watch available. I really want to stick with Garmin but I will jump ship if this isn't resolved. If it's something that can be resolved via software updates then I'm ok waiting but I'd hate to pony up the $ for the watch and later learn that it's a hardware issue and it won't be resolved. I'm sure you can see where I'm coming from.

                                Comment

                                Working...
                                X