Accurate running speed - gps v footpod

Thanks for the responses.

I decied to go for a Polar H10, actually got in with a discount for some reason. It arrived just now, and I can confirm that bthrm and the hrv app work. Until the two puckjs which I ordered arrive, I might play with accelerometer data coming from it, if I can figure out how.

When the puckjs arrive, I'll see if I can get it to trace out my steps to measure speed and distance, it would be super cool.

if you turn it on and start running immediately, the first few minutes it won't have many satellites, and as it gets more and gets more accurate the position it reports will fluctuate.

I always wait for the "GPS" in the lower left corner of the run+ app to turn green before starting a run (although once I ran out of patience, but usually it doesn't take long). I had a look just now at a gpx file though, and the first turn is clearly way off, but the rest is mostly not bad. There are some squiggles where I go under bridges though, which is another point for footpods, if they work.

There is something called 'kalman filter' that can be used to filter GPS coordinates/speed

Uh-oh, I do know some mathematics, but not so much statistics. I might dive into this to see if I can make it work, but I won't promise anything soon. But thanks for the tip, I'll see if I get anywhere.

they basically just stream the accelerometer data to a phone and get the phone to do the analysis

Do you think the banglejs is powerful enough for this sort of analysis? As a pure mathematician, I don't have a good sense for how much computation power is enough. My sense is that, theoretically, I should be able to use acceleration and gyro data to draw the curve of my foot for each step, using calculus. But wheather the watch (or puckjs) can do the computation in real time, I have no idea.

In terms of accuracy it'll be fine - it's probably got the same exact sensor as the Sryd

I can absolutely believe that :D

I used running footpods from the days before 😱 wrist based gps

I used to use a casio with a stopwatch back in the day. I would prepare and memorize an 8k/10k/14k route on google maps, and then write down my time in a little book :D

But yes, basically any footpod would do, but it seems to me that some of them use ant+, and not bluetooth. Banglejs doesn't support ant+, does it? A quick look at the webpages of some of the companies that sell footpods indicate that they only work with their watches. Even if it is maybe possible to get it to work with other devices, I would hesitate to buy one, if I don't know whether it will give any useful data.

But it seems to me that for such a device, there would be two distinct categories. One which calculates speed (as well as cadence, etc), and then sends that data over. It seems to me that this is what stryd does. The other category would be a device which send over accelerometer data, and then the receiving device is left in charge of computing the data to be displayed and logged. It seems to me that some of the garmin devices are in this category.

The former category would certainly be a nice, quick and easy solution. Even if it wasn't open source, having a black box that gives you this data would be great tool. If the puckjs can be programmed to serve such a function, this would be the best.

As for the second category, if it works, it would also be great. But if I have to program the banglejs, then I would see no reason not to use a puckjs, as long as it is accurate.

One of the difficulties seems to be simply distinguishing these cases, since the promotional material from any company just says it works well with their watch, and you're left guessing.

whilst you'll get a smooth trace the actual points are actually slightly off by a small amount each second, so for the overall trace it's fine and smooth, but if you actually take the instant data and use that to calculate pace then it jumps back and forth due to the small distances on the calculations

This makes a lot of sense, but I am surprised to mostly see banglejs underreport speed compared to garmin. If the points are jumping to the left or right, it should think it was going faster. I think this actually happened at some point when I was going under a bridge, but only for a moment.

Any code would be welcomed, to say the least. I hope I can put a bit of work into this project, and get at least an accurate cadence. It might take some time though.

Speaking of cadence, I'll just mention one last thing. On the wrist, banglejs gives a much lower value than the garmin, and I'm pretty sure the garmin is correct, since I used to actually follow a metronome function on the garmin, to get 180 steps per minute. Also, that data is coming from the garmin run dynamics pod, which clips on the waist, and should be pretty accurate. Unfortunatly, though, it is only ant+ (I think).