Baz wrote:
> I planned a route using Memory Map, the route was 8.3 miles
> At the end of the walk the trip odometer on the Geko read 8.1 miles
> MM showed the track to be 10.1 miles
> Am I doing something wrong? Or just expecting too much from my gear?
Almost certainly down to bad reception at some point during the walk.
Tracks are usually longer than routes since routes tend to have lots of
straight lines between relatively few points. The odometer and the track
should be a pretty close match if reception is good. If not, it may be due
to losing reception (where the odometer stops incrementing) or due to
spurious points in the track that add extra distance that you didn't
actually walk.
Dominic Sexton wrote:
> Firstly the odometer on the GPS will most likely under-read.
Perhaps, but not by much in my experience.
> These two will account for some of the discrepancy however the extra ~
> 25% you have seen here does seem to be larger than I would have
> expected....
Way larger. I've never encountered anything remotely like that, assuming
good reception of course. If the reception is bad then I don't take any
notice of the numbers.
Gordon Burns wrote:
> When I plot a route over the hills of Lakeland/Snowdonia I aim to get a
> route on Memory Map that is about 12 - 14 miles long. When I come back my
> tracklog usually reads about 16 - 17 miles.
Usually? If that's normal for you then you're either doing a lot of walking
in deep valleys or forests, or more likely, you're not placing your GPS
where it can get and keep a good view of the sky.
> I put this down to the inability
> to plot every little twist and turn on the map. That difference is not far
> short of 25%!
I put it down to bad reception. I'm sure that I never get results that bad
(assuming good reception) so I've just had a quick trawl through my diary
and picked out some sample data. I don't usually write the track length in
my diary (since the odometer is usually pretty reliable), but I found that I
did so in 2001 for a number of trips, so I've gathered the data for every
trip where I wrote both down.
8th Jan 2001 trip 4.3km, track 4.3km
12th Jan 2001 trip 9.1km, track 9.2km
3rd May 2001 trip 8.9km, track 8.9km
7th May 2001 trip 3.1km, track 3.3km
10th May 2001 trip 15.0km, track 15.0km (cycle)
12th May 2001 trip 12.0km, track 12.0km (cycle)
16th May 2001 trip 12.0km, track 12.0km (cycle)
20th May 2001 trip 9.7km, track 9.9km
24th June 2001 trip 15.4km, track 15.5km
25th June 2001 trip 13.2km, track 13.2km
9th Oct 2001 trip 4.3km, track 4.5km
17th Oct 2001 trip 7.2k, track 8.1k (Rhossili with Bill Grey)
24th Oct 2001 trip 7.9km, track 8.5km (Craig y Llyn with Bill Grey, Fran
etc.)
Out of 13 instances, the trip and track lengths match perfectly on 6 of
them. It's probably worth noting that three of those that match perfectly
were cycle rides, with the GPS positioned on the handlebars giving good
reception. Also the cycling was done in a good reception location, and the
relatively high speed and non-stop nature of the cycle rides may have
contributed to giving a more accurate result. These prove that the odometer
and track distances can match very accurately under good conditions.
On those that don't, the difference is only 0.1 or 0.2km, with the exception
of the last two, and even then, the difference is still less than a
kilometre, nowhere near 25%. I recall that the Rhossili walk involved a
deep valley, wooded in parts, so that was no doubt the cause of the bad
reception there, while the Craig y Llyn walk was done entirely in forestry
(but no deep valleys). In fact, there were only a couple of tiny breaks in
the last track, so it did surprisingly well there.
Paul