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Wanted: Someone cleverer than me
by Bruce Ure at 17:19 21/12/05 (Forum::Technical Advice::General)
My run data for last year's London Marathon, kindly recorded for me by my Garmin running GPS thing, had a number of errors, induced (I think) by the GPS signal being skewed by one or more tunnels I ran through.
Rather than pick up no data, which would have been preferable because the system interpolates from the surrounding data if it goes through a patch of bad reception, it actually picked up wrong data, which is way harder to correct for, in this instance anyway.

So, here (actual route) and here (GPS lies) we have two maps, one with the trace from the GPS, one with the actual route I ran. They are the same pixel size and more or less the same scale.

And here we have a (quite large) Photoshop file with one overlayed on the other, the top one at 50% opacity, which might help get a handle on it a bit better if you switch the layers on and off a bit.

And here we have the GPS data in the form of an XML file.

I have struggled with this for a few hours now and I'm not making much in the way of progress.

If it was just a training run, I'd not be bothered, but I want to keep the marathon data for posterity, and I want it to be right.


Can anyone help me munge the XML so that the trace resembles the actual route run?

It involves working out which points are responsible for the erroneous plots, and correcting them with sensibly-interpolated values from the good data either side.

Sounds easy, doesn't it.

A bottle of fine wine, or a toy, or something -- an as yet undecided present -- awaits the first person who can do it. Not to mention my undying gratitude.

If you need to test the new XML once changed, either I will need to do it, or else you'll need to steal the code from my run tracker page (http://ure.org.uk/diary/runmaps/workoutTracker.php, also there as workoutTracker.php.txt, and workoutTracker.js is there as workoutTracker.js.txt) and get yourself a Google Maps API key (free, and easy, from google). Unless there's some other way of testing it.


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Wanted: Someone cleverer than me Bruce Ure - 17:19 21/12/05
Re: Wanted: Someone cleverer than me Hugo van der Sanden - 01:15 22/12/05
I think I could probably help with that, or you might be able to do it yourself, but I don't have any of the tools to work with or visualise this information.

Do you have something that plots the XML data then lets you click on an individual point to examine it? Clearly the first glitch is when you suddenly jump off Marsh Wall - can you click on that point to get the details? Or failing that, do you know at what time you were there? Or failing that, is there an online map that will let you locate a place then ask the latitude and longitude? (I just looked at Google and Multimap, and couldn't see such a facility in either place.)

Once there is a way to relate the individual XML entries to specific points on the map, the rest is a simple matter of blood, sweat and tears. :)


Re: Wanted: Someone cleverer than me Bruce Ure - 03:13 22/12/05
Thanks Hugo, I will look in detail at this tomorrow but meanwhile I have found that I can convert the XML data into a differnt format and import it into Google Earth.

Then, get this, it will animate flying along the route, dammit. In perspective. Bloody hell... I nearly came. What an incredibly sexy application of internet technology. (Dave, I found you have to click on a "Path" in the left hand treeview list thing, then click the Play icon... it's exactly what we were looking for.)

Here is a screenshot of the dodgy area, in Google Earth. Imagine that tracking along all smooth, like, for the whole of the route, turning to reorientate as needed.



Re: Wanted: Someone cleverer than me Steve - 04:49 22/12/05
What did you use to convert the XML into a format that you can import into Google Earth?


Re: Wanted: Someone cleverer than me Bruce Ure - 09:24 22/12/05
A program at http://www.ccc-raab.com/transhstgpx/ converts Garmin's HST ('history') files into GPX ('GPs eXchange') which Google Earth understands (it's just a flavour of XML with a GPX extension).

I'm not sure what else (other than the ForeRunner 301) outputs HST, and in fact that only does so indirectly, via exporting from the Garmin Training Centre, and you have to export the entire history; there's no selection ability, meaning you have to manually edit the HST after exporting if you only want to import a subset of the data to GE.

Not sure if that helps, but.

If you fancy having a play with the Marathon fly-through, here's the GPX file (as yet uncorrected for the bad GPS data). Open it with GE and press the Play triangle in the treeview at the left.


Re: Wanted: Someone cleverer than me David Crowson - 13:04 22/12/05
Ahhh, cheers.

I'm just fully stoked that we managed to figure out how to export from Garmin Mapsource and into Google Earth. (by accident:)

I've been wanting a Topological map for plannning and Mapsource don't do Topos for Europe yet...but GE will do nicely :)


Re: Wanted: Someone cleverer than me Bruce Ure - 09:38 22/12/05
I have nothing that that will allow examination of an exact point of the XML data - even its originating program won't do this, much to my frustration already :-/

I can roughly work out what time I was where, possibly even to the nearest minute, but I think it would be more accurate to use your third method. I'm fairly sure that in the absense of something like Garmin's [heavily copy-protected] MapSource software, Google Earth or possibly even just Google Maps (maps.google.co.uk) can provide if not the pinpoint lat/long for the dodgy points then at least close enough to be searchable (with better accuracy than a minute).

I shall return to this later. I am just off to take Asha to see some lovely Christmassy play or something... the Gruffalo's Child, I think. Wonderful stuff.