10 ms·
four or five sig figs of internal pedometer step counts is rubbed up against four or so sig figs of phone-gathered GPS distance data after formal activities in
by VLM 8y ago
four or five sig figs of internal pedometer step counts is rubbed up against four or so sig figs of phone-gathered GPS distance data after formal activities in the fitbit app to fine tune your stride length. In my case my stride length is about 75.821 cm per step. Then it can use that calculated stride length to estimate distances when not doing official activities. As if my hiking boots are identical to five sig figs to my urban walking shoes or my sandals, LOL. Well, in theory, at least, its a good idea.
Fitbit UI, weirdly, explains what its doing but refuses to provide the actual numeric result.
To some extent its overkill... from my experience orienteering as a civilian and in the military, your average stride length might vary up to 5% based on conditions. You can't use dead reckoning alone to do land nav on foot for long distances, you need a map (or GPS). Which I guess is kinda the point of the fitbit needing GPS access. Doing theoretical calculations to 4 sig figs means at least on average its not too far off, and frankly most athletes use the same boring path every day with the same shoes etc so averaged track data is going to be more accurate than a wilderness land nav course anyway.
I have not decompiled the fitbit code or done anything illegal but IF I were to implement this I'd include GPS/map based ground slope data as a correction factor because I know that has a major impact on stride length. I have no idea if fitbit does that, but they should.
- brlewis 8y agoFitbit UI, weirdly, explains what its doing but refuses to provide the actual numeric result. Look under "How do I change my stride length?" on the page below. The same place you change it you can also see it. https://help.fitbit.com/articles/en_US/Help_article/1135 https://help.fitbit.com/articles/en_US/Help_article/1135 Disclosure: #fitbitemployee but speaking only for myself.
- tzs 8y agoI don't have a Fitbit, but I do carry an iPhone which includes a pedometer in the "Health" app. It's notion of stride length is interesting. I exported my daily step count and distance walked, and divided that later by the former to get the stride length. I plotted this data. step counts: https://i.stack.imgur.com/x0TPU.png https://i.stack.imgur.com/x0TPU.png distance: https://i.stack.imgur.com/sufma.png https://i.stack.imgur.com/sufma.png Both quite reasonable looking. Inferred stride length: https://i.stack.imgur.com/giz7V.png https://i.stack.imgur.com/giz7V.png Note that it breaks down into 5 distinct regions, with very sharp boundaries between them. Within each region the stride length has a fairly level average but a lot of variation around that. When you cross a region boundary, same patter but the average shifts down (sometimes dramatically, such as the shift in early 2016). I have no explanation for any of these shifts except that last one and maybe the small one around Oct 2016. The last one, in the middle of 2018, corresponds to my changing phones from in iPhone 6 plus to an iPhone x. That small one before that matches up with when we switched to full time work at home The earlier shifts were all on the iPhone 6 plus, and as far as I can tell do not correlate with iOS updates, or with anything in my life that might change my stride size such as seasonal changes (I probably take smaller strides in winter) or getting new shoes. I asked about this on apple.stackexchange.com, but it got no answers or comments, a down vote, and was automatically deleted as a dead question.