Another mid-air (UK)

In article son_of_flubber writes:
On Thursday, August 7, 2014 11:46:30 AM UTC-4, Ramy wrote:
Even with 8m accuracy, It is more than sufficient for accurate collision=
avoidance, unless someone considers half a wingspan not accurate enough fo=
r collision warning with another glider or obstacle.=20

Prompted to comment here by my Geek Fascination Syndrome (GFS)...

I'd guess that the error on each position fix is not significant. Flarm is =
computing trajectories from multiple position fixes, so a maximum +/- 8M er=
ror for each fix will be smoothed out by the statistical distribution of a =
large number of position fix errors. Some of the errors are + and some are =
-. Average 100 GPS position fixes and you will get a pretty accurate positi=
on.

Not so much as you might expect. The error varies more slowly over
time. If those 100 fixes were taken one every hour or two, then they
would average out much better than fixes taken once per second.

The fact that the error moves more slowly helps the trajectory calculation
as successive samples will have a similar error.

Alan