GPS-Sport ForenRun.GPS GeneralHxM distance and speed accuracy disappointing ?
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Lee_Nover 21.12.2009 18:59:39 UTC

HxM data

cadence can be measured in any direction. Zephyr HxM detects and transmits data for 3-axis. Speed and distance should only take into account X & Y axis, ignoring the Z (vertical) axis. I'll probably also request the SDK to check the data that could be used :) if you feel you're close to a release of your SW, I could help test it (on Touch Diamond wm6.1 + Zephyr HxM).
gmngueko 21.12.2009 18:20:51 UTC geändert am 21.12.2009 18:21:35 UTC

calibration under study

I believe yes it should be possible to calibrate it, my current experiment shows that the 30% overestimation while running and around 15% under-estimation while walking are quite constant. So for me it should be possible to calibrate it.

I'am writing my own small mobile application to work with the HxM (yes I got the HxM SDK kit and visual studio) So very very soon I should be able to display everything and do the calculation on the data.
Actually I have nearly finished I can display all the info of the HxM on my mobile, the only thing remaining is to study the data to see how to calibrate it (based on speed or based on the cadence or both ???.....).

I have already see that by just jumping up and down, but staying at the same place, fools the HxM, so it looks like the vertical acceleration is the main info they used to calculate the speed and then the distance.
Lee_Nover 21.12.2009 18:04:40 UTC

accuracy

I can also confirm a +30% missmatch between HxM speed/distance data and the one from a treadmill. (why I checked the forums)
can this somehow be calibrated?
Tom 08.11.2009 16:54:57 UTC



Today I did a test running with GPS and G-Sensor. You can see the results below. G-Sensor recorded 11 % more distance than GPS (which we assume is the real distance).

One thing I think is important to mention because some might not have realized it: The value "G-Sensor distance" is NOT counted for a training session, it is the TOTAL distance recorded since the application was started and the HxM connected.

I'll do more testing with bike etc.

[1]Short test run with HxM and GPS
gmngueko 08.11.2009 01:17:20 UTC geändert am 08.11.2009 01:18:32 UTC

at least dump GPS latitude longitude with g-sensor distance

ok, but you could still put in the csv the latitude and longitude of the GPS, but give a choice(via configuration parameter) to put the speed/distance from g-sensor or speed/distance from gps.
so that way I could still be able to analyse off-line the gps distance, because with software like sporttracks, which I use, I can calculate myself the distance from the GPS latitude-longitude, and then compare it to the distance from G-sensor in csv.
Tom 06.11.2009 09:41:42 UTC



Yes you're right it would be better to have both in the CSV file. The problem about this is that the internal data formats allow only one distance value (they are optimized for size).

So the hypothesis so far is: the higher the speed is, the less accurate is the distance coming from G-Sensor. It should be correct for speeds from 5 km/h to about 40 km/h (it's not intended for car driving).

We'll do further testing.

gmngueko 06.11.2009 08:56:35 UTC

G-sensor info together with GPS info in csv will be better

my test indicates to me that while running the error is greater than when walking.
also currently you only put one distance in the csv file, it will be better if you could put the g-sensor distance and speed together withthe GPS distance and speed in the csv file, that will allow me to choose the input I want to use, it will also help understand better the differences between the two.

currently I'am force to switch off the GPS and use my edge 305 as gps recorder which is odd.
Tom 05.11.2009 22:43:07 UTC



I did another test with the HxM today (walking 2.6 km) and it was a perfect match! GPS said 2.58 and HxM said 2.56 km. We need to find out under which conditions the results are worse.

The test was done with a Touch HD with internal GPS and a Zephyr HxM. You can see the training data here:
http://www.gps-sport.net/trainings/_193394
(but without HxM distance data as this is not uploaded).

To compare HxM and GPS accuracy, you can easily configure yourself a screen showing these values:
- Distance (coming from GPS if the GPS is on and signal is ok)
- G-Sensor Distance (coming from HxM)
- Speed
- G-Sensor Speed
[1]Screen configured for comparing G-Sensor and GPS data
Dima 02.11.2009 15:56:29 UTC



I can say that I tried HxM on my stepper, and HxM tells me that I go about 1 km in 20 minutes - very funny :)))
runnersfreund 18.10.2009 16:10:25 UTC

hxm

thanks for thinking about the problem. gps is not really a problem cause it´s either running or not, it is not delivering wrong data. that´s why the hxm is annoying. even when it´s running, you cant trust. it´s loosing connection or pretends i´m running with incredible speed.
the internal gps is not too bad, even when it takes its time to start which i agree. two gadgets with bluetooth are no problem, i´m using jaybirds and its running prefectly. i will try with diferent ports so they are running better (I hope).
i will report the results if they are helpful for others.
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