[OSM-talk] GPS track precision (was "GPS track upload working?")

[Ed Avis]

>From my experience with my Garmin unit (which, ironically enough, does not save
error values with the track logs, but does show an error circle on screen), the
GPS error does give a reasonable indication of when the current position is
likely to be inaccurate (for example when inside a building).  Filtering out
points with large error values would remove a lot of the junk from my track logs.

So I think it would be a good idea to include the hdop field in the database. 
Old track files have probably been traced by now, so it wouldn't be terribly
important to reparse them all just to add the field; just include it for new
uploads.

As others pointed out, it is just a tiny number that should be storable in one
byte per trackpoint.  (Perhaps if the column is nullable it might need more than
a byte, but you can do something clever like picking 255 as a special value.)

Perhaps not every device generates useful hdop values, but clearly some do (like
mine).  And not every device includes them in GPX output (mine doesn't), but
some do include them.  I just hope the intersection of the two sets is nonempty!

-- 
Ed Avis <eda at waniasset.com>