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Instantaneous pace steady but slow (possibly since 19.20 software update)

stephen.e.cox
over 3 years ago

I've noticed a persistent issue in the last couple of weeks. I didn't, unfortunately, notice when my software updated to version 19.20, so I can't say for sure that this is just related to the recent software update. My instantaneous pace during runs looks pretty steady, but it will be persistently low for long portions of runs. For example, today during an easy trail run (flat terrain) I watched my instantaneous pace during a full kilometer of running at about 5 min/km pace. The whole time, the watch showed my pace between 5:40 and 6:30, which is implausibly slow. When the auto lap completed for that kilometer, however, it showed a lap pace of 4:55. 

In the past, the instantaneous pace would only be that far off when I had a GPS issue, and it would usually overcorrect in the other direction when trying to correct my location. Now, there is nothing wrong with my recorded GPS track, and the lap paces all come out fine, so I am guessing this is a result of a heavyhanded attempt at quieting the occasional spikes in instantaneous pace that used to occur. Has anyone else noticed this recently, or is it possible there's just something wrong with my watch?

  • 0 over 3 years ago in reply to silentvoyager
    silentvoyager said:
    Garmin pace algorithm in not better with transition from uphill to downhill either.

    When I go uphill, my instant pace oscillates between too fast and too slow - the pace plot looks like a sine-wave. This happens in what I'd consider good GPS conditions.

    I assume this is because I slow down quite a lot, and probably I an staying within the GPS error margin between GPS fixes. If I had a choice of accelerometer inputs to help out there, I'd rather have an accelerometer in the chest area for correction, not on the wrist. 

  • 0 over 3 years ago in reply to 5135968

    VERY interesting discussion now  and ! Unfortunately I don't have so much time to interact today but I will be back in the discussion later on today or tomorrow.

    I ran my .FIT file from a run 2021-11-18 in the simulator to post this graph with similar data as silentvoyager posted some posts ago. The run was a Base run with some variations in speed to test the algorithm. The simulator seems to cause some odd behaviour in red line (drop-outs), these doesn't occur in the device. I'm working on to create a more smooth speed/pace which reacts as quick as possible to speed/pace changes. The built-in speed is too smothered and reacts too slow for me and hopefully I can improve the algorithm more over time.

    • Blue line is the built-in device speed in m/s
    • Green line is my custom algorithm CIQ speed in m/s
    • Red line is raw GPS speed in m/s (1 second interval)

  • 0 over 3 years ago in reply to AndersB

    OK, here is data from a short run today, which shows many more device pace dropouts.


    This compares the device reported speed (blue) with the GPS 1-second (grey), 10-second (yellow), and 30-second (green) rolling average speeds. All speeds are in meters/sec.

    There were actual stops at around 5:00, 7:30, and 26:00. The middle part from 5:00 to 26:00 is in a local park, on trails, and with varying tree cover. As you can see in the middle part of the run, the device speed, for the most part, stays well below the 30-second average GPS speed. That should never be the case, right? That shows a clear bias towards slower speed.

    There are a few pretty significant dropouts lasting 1-3 minutes each and one example where the device speed overcompensates at 20:00.

    Overall this is pretty horrible! For example at around 12:00 the difference between the device pace and the 30-second average GPS pace reaches 2:30-3:00/mile.

    elapsed: 0:11:30   dist:  1954.71  gps_dist:  1978.94  dist_diff:  24.23   pace: 10:41   1_sec_pace:  7:30   30_sec_pace:  8:00   m_pace:  8:05   spm: 84
elapsed: 0:11:31   dist:  1958.65  gps_dist:  1982.93  dist_diff:  24.28   pace: 10:39   1_sec_pace:  6:43   30_sec_pace:  7:57   m_pace:  8:04   spm: 84
elapsed: 0:11:32   dist:  1963.02  gps_dist:  1987.37  dist_diff:  24.35   pace: 10:34   1_sec_pace:  6:02   30_sec_pace:  7:52   m_pace:  8:02   spm: 84
elapsed: 0:11:33   dist:  1967.28  gps_dist:  1991.70  dist_diff:  24.42   pace: 10:29   1_sec_pace:  6:12   30_sec_pace:  7:48   m_pace:  7:58   spm: 84
elapsed: 0:11:34   dist:  1971.22  gps_dist:  1995.69  dist_diff:  24.47   pace: 10:29   1_sec_pace:  6:43   30_sec_pace:  7:45   m_pace:  7:55   spm: 85
elapsed: 0:11:35   dist:  1974.29  gps_dist:  1998.90  dist_diff:  24.61   pace: 10:29   1_sec_pace:  8:22   30_sec_pace:  7:44   m_pace:  7:52   spm: 85
elapsed: 0:11:36   dist:  1977.26  gps_dist:  2002.09  dist_diff:  24.83   pace: 10:29   1_sec_pace:  8:25   30_sec_pace:  7:43   m_pace:  7:50   spm: 84
elapsed: 0:11:37   dist:  1979.00  gps_dist:  2003.87  dist_diff:  24.87   pace: 10:29   1_sec_pace: 15:01   30_sec_pace:  7:51   m_pace:  7:50   spm: 83
elapsed: 0:11:38   dist:  1980.96  gps_dist:  2005.83  dist_diff:  24.87   pace: 10:32   1_sec_pace: 13:42   30_sec_pace:  7:59   m_pace:  7:50   spm: 83
elapsed: 0:11:39   dist:  1984.22  gps_dist:  2009.17  dist_diff:  24.95   pace: 10:39   1_sec_pace:  8:02   30_sec_pace:  8:01   m_pace:  7:50   spm: 84
elapsed: 0:11:40   dist:  1987.05  gps_dist:  2012.01  dist_diff:  24.96   pace: 11:03   1_sec_pace:  9:25   30_sec_pace:  8:06   m_pace:  7:51   spm: 85
elapsed: 0:11:41   dist:  1990.96  gps_dist:  2015.92  dist_diff:  24.96   pace: 11:03   1_sec_pace:  6:52   30_sec_pace:  8:06   m_pace:  7:50   spm: 85
elapsed: 0:11:42   dist:  1995.05  gps_dist:  2020.04  dist_diff:  24.99   pace: 10:43   1_sec_pace:  6:31   30_sec_pace:  8:06   m_pace:  7:47   spm: 84
elapsed: 0:11:43   dist:  1998.50  gps_dist:  2023.49  dist_diff:  24.99   pace: 10:43   1_sec_pace:  7:46   30_sec_pace:  8:04   m_pace:  7:45   spm: 84
elapsed: 0:11:44   dist:  2001.53  gps_dist:  2026.53  dist_diff:  25.00   pace: 10:41   1_sec_pace:  8:50   30_sec_pace:  7:59   m_pace:  7:44   spm: 84
elapsed: 0:11:45   dist:  2004.33  gps_dist:  2029.45  dist_diff:  25.12   pace: 10:39   1_sec_pace:  9:10   30_sec_pace:  7:56   m_pace:  7:45   spm: 85
elapsed: 0:11:46   dist:  2007.65  gps_dist:  2032.89  dist_diff:  25.24   pace: 10:41   1_sec_pace:  7:47   30_sec_pace:  7:53   m_pace:  7:46   spm: 85
elapsed: 0:11:47   dist:  2011.51  gps_dist:  2036.78  dist_diff:  25.27   pace: 10:48   1_sec_pace:  6:55   30_sec_pace:  7:47   m_pace:  7:47   spm: 85
elapsed: 0:11:48   dist:  2015.36  gps_dist:  2040.81  dist_diff:  25.45   pace: 10:48   1_sec_pace:  6:39   30_sec_pace:  7:42   m_pace:  7:49   spm: 85
elapsed: 0:11:49   dist:  2018.77  gps_dist:  2044.45  dist_diff:  25.68   pace: 10:39   1_sec_pace:  7:21   30_sec_pace:  7:41   m_pace:  7:50   spm: 84
elapsed: 0:11:50   dist:  2022.48  gps_dist:  2048.40  dist_diff:  25.92   pace: 10:39   1_sec_pace:  6:48   30_sec_pace:  7:42   m_pace:  7:50   spm: 83
elapsed: 0:11:51   dist:  2024.91  gps_dist:  2050.87  dist_diff:  25.96   pace: 10:39   1_sec_pace: 10:50   30_sec_pace:  7:48   m_pace:  7:51   spm: 83
elapsed: 0:11:52   dist:  2027.43  gps_dist:  2053.48  dist_diff:  26.05   pace: 10:34   1_sec_pace: 10:19   30_sec_pace:  7:50   m_pace:  7:53   spm: 83
elapsed: 0:11:53   dist:  2031.75  gps_dist:  2058.08  dist_diff:  26.33   pace: 10:34   1_sec_pace:  5:50   30_sec_pace:  7:45   m_pace:  7:54   spm: 83
elapsed: 0:11:54   dist:  2035.83  gps_dist:  2062.48  dist_diff:  26.65   pace: 10:36   1_sec_pace:  6:05   30_sec_pace:  7:45   m_pace:  7:53   spm: 84
elapsed: 0:11:55   dist:  2039.51  gps_dist:  2066.19  dist_diff:  26.68   pace: 10:36   1_sec_pace:  7:14   30_sec_pace:  7:42   m_pace:  7:52   spm: 84
elapsed: 0:11:56   dist:  2042.07  gps_dist:  2068.79  dist_diff:  26.72   pace: 10:36   1_sec_pace: 10:19   30_sec_pace:  7:45   m_pace:  7:53   spm: 84
elapsed: 0:11:57   dist:  2044.91  gps_dist:  2071.67  dist_diff:  26.76   pace: 10:34   1_sec_pace:  9:20   30_sec_pace:  7:49   m_pace:  7:53   spm: 84
elapsed: 0:11:58   dist:  2047.59  gps_dist:  2074.41  dist_diff:  26.82   pace: 10:32   1_sec_pace:  9:47   30_sec_pace:  7:52   m_pace:  7:55   spm: 85
elapsed: 0:11:59   dist:  2050.91  gps_dist:  2077.80  dist_diff:  26.89   pace: 10:32   1_sec_pace:  7:54   30_sec_pace:  7:51   m_pace:  7:56   spm: 85
elapsed: 0:12:00   dist:  2053.89  gps_dist:  2080.89  dist_diff:  27.00   pace: 10:32   1_sec_pace:  8:42   30_sec_pace:  7:54   m_pace:  7:57   spm: 85
elapsed: 0:12:01   dist:  2057.49  gps_dist:  2084.57  dist_diff:  27.08   pace: 10:32   1_sec_pace:  7:17   30_sec_pace:  7:55   m_pace:  7:58   spm: 85
elapsed: 0:12:02   dist:  2060.79  gps_dist:  2087.96  dist_diff:  27.17   pace: 10:25   1_sec_pace:  7:56   30_sec_pace:  8:00   m_pace:  7:58   spm: 85

  • 0 over 3 years ago in reply to silentvoyager

    Yes, very much deviations in that one! Do you want to share that .FIT file through PM? Would be interesting to run it in the simulator. Slight smile

  • 0 over 3 years ago in reply to silentvoyager

    You ought to try to get that to someone in Garmin who understands these things - the drop-outs you show there are very clear and obvious - where pace is consistently below your real speed for several minutes that wouldn't be acceptable for me.

    You'd need to go way above the standard customer support level who will just tell you to update .CPE files, or reboot....support can be absolutely clueless. They won't understand any of that.

  • 0 over 3 years ago in reply to 5135968

    Its not so easy to get in contact with the developers. I earlier had some discussions with Garmin Chris about this issue and my input was going to be sent further but I haven't heard anything about it since then.

  • 0 over 3 years ago in reply to silentvoyager

    Here is the result after running your .FIT file through the simulator. The odd instant GPS speed dropouts occurred with your file also. So, it must be some glitch in the simulator. As you can see my green line is not identical to your and that is due to that my algorithm uses weighted data points and also uses some cadence changes to identify speed changes. 

    Can you see any big errors in the green graph line? If, so, where do you see them?

  • 0 over 3 years ago in reply to AndersB

    The area I have circled in red looks suspicious - cadence is actually low at that point, but your datafield is showing a big spike in pace there. Can you plot that against elevation as well?

  • 0 over 3 years ago in reply to 5135968

    True! I will do another simulation which also includes the elevation. It takes about 30 minutes.

  • 0 over 3 years ago in reply to 5135968

    Here is a new graph with elevation included. Your marked area looks a little bit different this time. It might have been a glitch in the simulator last time. The simulator seems non-consistent with the data.