[OSM-talk] logging with precission/amount of data set to maximum

Joerg Ostertag (OSM Munich/Germany) openstreetmap at ostertag.name
Thu Sep 7 12:19:49 BST 2006


On Thursday 07 September 2006 12:08, Richard Fairhurst wrote:
> Etienne <80n80n at gmail.com> wrote:
> > It should be noted that recording 1,000,000 tracklogs does not
> > *automatically* guarantee one of these things.  Some user called SteveC
> > has apparently uploaded over 6,000,000 trackpoints but hasn't got a
> > mega-star. It's rumoured that he bought most of his trackpoints from a
> > courier company ;-)
>
> I don't really have a problem with the megastar idea - it's just a bit of
> fun.
>
> But as per the other day's conversation, it does discriminate against
> those of us who use old eTrexs with auto track compression. :(

I wouldn't use this feature even if i had it. Since this makes later 
computations very flaky and difficult. So if you have enough memory available 
in your gps it would be great to have all track points stored. This way 
you'll be able to see much more things in the track logs than you currently 
see.
Just giving one example:
I store my tracks locally in plain NMEA! A little more data, but a lot more 
information i later can count on.

Example Sattelites in View:
Take the satellites in view. Lets assume x is got a lock and o is no 
reception. If you see the following pattern on your satellites in view while 
driving:

        N
     o  |  x
      o |  x
 W -----+------ E
      o | x  x
     o  |   x
        S

and then after some driving you suddenly see the following:

        N
     o  |  o
      o |  o
 W -----+------ E
      o | o  o
     o  |   o
        S

You can make some suggestions on the buildings near you. Since the buildings 
block the GPS-signals you have a bad reception with buildings and a good 
reception without buildings. This can be taken as a suggestion for filling 
the abutters=xx tags.

Example Speed:
If you have the speed driving along a road you can get a pretty good guess 
which highway= tag this part of the street would be appropriate to tag.
Some of you might think; that is no problem, we have the timestamps and the 
position, so we can calculate the speed later too. But the timestamps in your 
gpx log have a precision of 1 second. So the speed might vary by almost 
factor 2 (between 1 sec and 1.9sec) which for example at 90Km/h could also be 
180Km/h which is not really precise. If you get the speed directly from the 
GPS device its evaluated by measuring the Doppler shift of your signal which 
is pretty precise (less than 1Km/s error).


These are only some examples why I always would store the maximum data I can 
get and handle from my GPS devices.
So I would ask everyone to log with 1 point/second and if possible also things 
like dop,alt,speed,sats-in-view, ...

-

Joerg






More information about the talk mailing list