Nick (Scots) said:Estimating GPS points to 10 figs is poor accuracy.
As Simon said, in the case of trig points they aren't estimates. Neither
are actual GPS readings taken at summits (they may not be absolutely
correct, but they're not estimates). Likewise grid refs taken from mapping
software (Anquet etc.) are not estimates, they are what the software reports
(again probably not that accurate, but not estimates - 50k GRs can sometimes
be way off, but 25k GRs are usually pretty close).
But the key point is that 10 figure grid refs is what GPS receivers use, so
that's what the GRs should be listed as, even if the last figure is a 0 or a
5. Some people have problems entering a 6 figure GR into a GPS, and that
would be hopelessly inaccurate anyway. An 8 figure GR would be best IMO,
but a GPS requires 10, so you have to pad it out no matter what the 5th
digits are.
Besides, how many people actually follow the GOTO arrow to the actual grid
ref? Even in thick fog you can see a summit within 10m. Once you get that
close you tend to stop looking at the GPS anyway, so the 5th digits tend to
be irrelevant in practice.
Speaking of actual accuracy, I have a local "test" trig that I often pass,
so I always stop to take a reading. It's almost always within 3m of the OS
stated grid ref.
Likewise, grid refs that I've marked myself tend to have similar accuracy,
on the same day at least. Whenever I get back to my car the ending GR tends
to be within 2-3m of my starting GR (I always mark the start and end grid
refs), although the error would probably be greater on other days. When I
have multiple waypoints for a particular summit, I tend to average them for
better accuracy. It still isn't 1m accuracy, but it's better than 10m
accuracy.
Who knows, if Egnos ever gets up and running, we should get even better
accuracy.
Paul
