On 18/02/2020 14:54, Nick Maclaren wrote:
Not very good. Yesterday, according to a GPS logging app, I ascended
just shy of 3,000 feet. The actual figure would be more like 700 or 800
feet. The difference is because there's a lots of noise, of substantial
magnitude, in the altitude reading.
What I've read if you want an accurate altitude to use the latitude and
longitude to interrogate a detailed terrain database. But it requires a
lot of detail to handle steep slopes. If you're on the edge of a cliff,
even that doesn't help, since there's the horizontal error to take into
As I said earlier, with the screen on, my tablet battery is exhausted
after about 3.5 hours. But provided the screen isn't permanently on a
powerbank can recharge it faster than it's being used.
The Garmin Glo seems to be slightly more accurate (less noisy) that the
Etrex 20, consistent with a reported accuracy of 1-3m, rather than 3-5m
(and much more accurate that the tablet's native GPS). Track distances
come out slightly shorter than, which is consistent with that. (There
may be a countervailing factor of more points, so corners aren't cut on
the measurement.) It looks as if in both cases the figures overstate the
accuracy - if you repeat a route there can be systematic differences
betwween the track greater than the reported accuracy. Perhaps this is
due to accounting for echoes, which will differ because of satellite
The Garmin Glo seems to be more effective indoors, which may make it
more useable in a train - the Etrex 20 is more often than not dead on a
train, as is the tablet's native GPS.
The big advantage over the Etrex 20 is that I can capture grid
references directly into my field notes - there's an app which will
paste the GR to the Android clipboard, which I can then paste into my
notes. Handy for biological and geological recording, and other
applications looking for high precision position records.
> Nick Maclaren.