[talk-au] Hi all ...

Sam Couter sam at couter.id.au
Sat Jun 20 12:09:50 BST 2009


Ross Scanlon <info at 4x4falcon.com> wrote:
> As I said if you have a really good reason to change a source=survey then
> do so but don't change it just because it's your trace and you think yours
> is the only correct one.  Leave it alone if your not sure.

If I can only see one trace (mine) because you didn't upload yours, all
available evidence points to my trace being the most accurate source of
information. If ten people did the same thing you can expect the way to
shift around ten times. If ten people instead upload their traces, the
way won't shift very far unless the first trace was very different to
the rest.

> Averaging the traces will not necessarily make the map more accurate.  If
> there are two that correspond closely and one that's 20m off then the
> resultant way will be incorrect.

I think you've shown yourself to be smart enough that you know this is a
strawman.

The term "average" usually means the mean, which would cause the result
you describe. I don't think you fooled anyone into believing that would
happen, or even that you think that would happen. When using GPX traces
it makes most sense to use the mode or something approximating it, or an
intuitive weighted average. Any of these methods would discard the
outlier and result in more accurate maps on average (there's that word
again, meaning something different again).

You don't have to upload GPX tracks, or geotagged photos, or your
running commentary audio notes, or anything for that matter. But if you
don't then you're being less useful than you would otherwise be. You're
not being paid, so you're under no obiligation. You asked "Why should
I?" and a lot of good reasons have been given.
-- 
Sam Couter         |  mailto:sam at couter.id.au
OpenPGP fingerprint:  A46B 9BB5 3148 7BEA 1F05  5BD5 8530 03AE DE89 C75C




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