Another mid-air (UK)

At 16:06 07 August 2014, son_of_flubber wrote:
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.

I'd expect that the sampling rate is high enough to make the
trajectory
cal=
culations quite accurate. If the sampling rate was not fast
enough they
co=
uld put a faster processor into the units. Plus as Ramy pointed
out,
FLARM=
must be alerting for 'possible near misses' because there will
be small
de=
viations in trajectory caused by turbulence and pilot control
inputs.

The 8M 'error' of GPS is unlikely to be the critical factor that
keeps
FLAR=
M from fulfilling its mission. I'd bet that the critical factor is the
hum=
an pilot, that being the most inherently error prone and
undependable part
=
of the system.


+-8m 95% of the time is best case, under ideal conditions and
installations. Do you fly only in ideal conditions and have an
ideal installation? f the answer is 'no' your error will be larger.
Also this is 2D error. As everyone 'knows' and goes on ad-
nauseam, GPS vertical error is significantly worse.

Have you 'any' evidence for the rest of your post or is it just
pure supposition? If you analyse the data rate and bandwidth
requirements of the data link you'll realise what you suggest is
impossible