...can be substantial
I guess it is all down to the databases that various software packages use but I get widely (wildly) different figures for the same .gpx file for a route I've planned in the Maritime Alps...
A scale for me from 1. 'ooo me legs' through 2. 'good day out' to 3. 'walk in the park'
It does not really help when planning longer routes....but I guess that's what you get for overplanning and a fascination with digital mapping..
I've been looking at gpx tracks/routes quite a bit lately. Height data is quite course - 50m squares for the free OS data which a lot of online mapping sites use - with the consequence that tracks often have vastly inflated ascent/descent figures due to jitter across the squares. Routes, as you plot when planning, tend to be more course than the data so it has less effect. But, umm, obviously the data sources can be very different too: survey methods, and when. The Merkins have just about everywhere plotted to 90m resolution: height-data, which I get the impression a lot of mapping uses.
Not that any of this helps you, to decide which is most accurate or otherwise, at all!
Well it is the same problem as encountered when They first tried to measure our coastline. If you used one scale you'd get one result an finer scale gives a different result again. If you could actually measure the coast (or route) down to the atomic scale you'd actually get it to be even greater distance. I think a 90m block should give a lower figure than a 50m block that someone above mentioned.
Personally I'd just ask for advice on what the area is like for walking from someone who has been there. What I mean some places the ascents are not too bad, comparable to say Dales or Lakes. Other places the ascents are brutal. If someone can say it is like the first or the second you just treat the route accordingly, namely reduce the distance if it has brutal terrain or increase the route if it is easier. You can always see for yourself and modify the routes taken once you have a feel for the place too. At the end of the day better to enjoy it than stick to some route worked out before you got there that you can't enjoy because too hard or easy. Better a level 2 worked out when there than rigidly sticking to a walk itinerary set out before you'd got there.
linky to elevation data explanations
an excellent explantion and things by the capt and others.
Beth - Ozi was a first port of call - cheers
Parky - most useful; thanks.
It's an irritating inconsistency isn't it?
I recently checked out a bike ride ahead of a charity event in a couple of months. I recorded one figure with my Suunto Altimax and another with my gps (etrex 30 with inbuilt barometer). I took the recorded track from the gps to my PC... Mapyx Quo gives me two different results depending whether or not I choose "Uses DMT Interpolation" (whatever that is), and Garmin Basecamp gives yet another (lower) figure. So after my recce actually undertaking the entire route I've got 5 different answers, varying from 1550m to 2000m (over 53 miles).
I think I'll just quote the highest one when I'm asking folk to sponsor me and the lowest one when I'm persuading other folk to join in the event
I'm not sure DTM (oops, I was still waking up) Interpolation can depend on the use or not of any gps-recorded data.
I say this because it's an option in the elevation profiling of any route or track in Quo, i.e. more than likely to be one you've just plotted directly on the PC rather than importing from gps. And even with an "internal" track like this you get two different answers with or without Interpolation. So it has to be something to do with the algorithm the software uses to process it's own digital data model.
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