OpenStreetMap 開放街圖
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!
討論
由 EdLoach 於 2013年07月 3日 16時19分 發表的評論
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).
Ed
由 EdLoach 於 2013年07月 3日 16時21分 發表的評論
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.
由 HannesHH 於 2013年07月 3日 16時27分 發表的評論
Check osm.wiki/Edit_GPS_tracks for more tools, I can recommend GPSBabel
由 Vclaw 於 2013年07月 3日 17時58分 發表的評論
Or you can set the visibility options for the traces. See osm.wiki/Visibility_of_GPS_traces
If you set a trace as “Trackable”, then it won’t be linked to your account.
由 robbieonsea 於 2013年07月 3日 22時39分 發表的評論
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 osm.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…
由 FTA 於 2013年07月 4日 02時30分 發表的評論
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.