[OSM-talk] GPX trackpoint stacks

[Robert Hart]

> Given that 6.5m are in stacks of more than one, and 7.3m points share
> the same tile, then either the same track points have been uploaded
> repeatedly, OR GPS receivers have some form of rounding function causing
> GPX points to snap to grid. It could be the case that GPS receivers
> generally use single precision for their internal representation.

$ grep 51.377 gps/*.gpx | sed -e "s/.*lat..//" -e "s/. lon.*//" | sort |
uniq -c
      3 51.377434731
      2 51.377456188
      3 51.377477646
      9 51.377499104
      9 51.377520561
     10 51.377542019
      4 51.377563477
      7 51.377584934
      2 51.377606392
      3 51.377627850
     16 51.377649307
      7 51.377670765
      1 51.377680823
      4 51.377692223
      3 51.377713680
      3 51.377735138
     10 51.377756596
      6 51.377778053
      5 51.377799511
      2 51.377799762
      8 51.377820969
      7 51.377842426
      7 51.377863884
      5 51.377885342
      3 51.377901603
      5 51.377906799
     12 51.377928257
      9 51.377949715
      3 51.377949798
     10 51.377971172
      5 51.377992630

In most cases the difference between two adjacent latitude values in the
list is 0.000021458 degrees. 360/0.00002146 = 16776959 = 2^24 (or near
enough to make no difference).

So my garmin is quantising to equivalent of 2.4m if my math is correct.... 






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