GPS TracesPosted by FTA on 3 July 2013 in English (English).
Well, after learning I would be traveling on a long trip for summer vacation, I decided I wanted to play with GPS traces. I settled on the OSMTracker for Android because of the ease of tracking without the requirement for data access (I don’t have unlimited on my mobile, so I was not interested in racking up a big bill). I was able to capture most of the trip on the tracker and exported the GPX files to my laptop. It was a little disappointing to me that I could not upload a trace attributed to my name without having to include the time data; I am not really interested in a retroactive speeding ticket due to data I freely uploaded onto the internet if I did exceed the limit in places.
Regardless, I was able to get some traces in rural parts of the USA where it doesn’t seem there have been traces before. My hope is to get traces in the opposite lanes on the way home. In the future, I plan to utilize this more with mapping walking/biking trails as well as outlines of new buildings not yet shown on satellite imagery. Until next time, happy mapping!
Comment from EdLoach on 3 July 2013 at 16:19
In case it is of interest, GPX_Editor has a menu option to anonymise the times (I’ve not tried the option so don’t know exactly what it does).
Comment from EdLoach on 3 July 2013 at 16:21
It seems I can’t edit previous comments. It sets the start date/time to 01/01/1900 00:00:00Z and counts up in seconds.
Comment from HannesHH on 3 July 2013 at 16:27
Check http://wiki.openstreetmap.org/wiki/Edit_GPS_tracks for more tools, I can recommend GPSBabel
Comment from Vclaw on 3 July 2013 at 17:58
Or you can set the visibility options for the traces. See http://wiki.openstreetmap.org/wiki/Visibility_of_GPS_traces
If you set a trace as “Trackable”, then it won’t be linked to your account.
Comment from robbieonsea on 3 July 2013 at 22:39
Note that GPS_Editor applies a constant time diff to each point. The time difference between points is kept - thus calculating speeds between points is still viable - and could point to where one has exceeded the speed limit.
However post calculating ‘instantaneous’ speeds from GPX tracks is not reliable since the standard only has an accuracy rounded to the nearest second. Often my GPX tracks from a Garmin Nuvi saving every second means I can get speeds over 100mph, when otherwise going slowly (or a spurious point)!!
Averaged over a several trackpoints should give a more robust speed value - and hard to deny that would be due to spurious points (especially if a median or modal average is used).
I don’t know if the OSM Traces API will allow all trackpoints having the same timestamp - as that would be the only way to remove speed inferences. According to http://wiki.openstreetmap.org/wiki/API_v0.6#GPS_traces - it says “trackpoints must have a valid timestamp”, thus setting all points to 01/01/1900 could be feasible.
Unfortunately it will not help people trying to process these files to gather speed statistics ;)
NB2 that GPS_Editor is Windows only.
Goes off to consider adding some kind of Anonymize Time function to Viking (http://sourceforge.net/projects/viking/) which I maintain…
Comment from FTA on 4 July 2013 at 02:30
Thanks all for the comments! I’ve decided for the sake of determining proper speed limits, I will keep most of my traces public, as they are in-city. However, I will definitely have to check out some of the tools mentioned.