[OSM-talk] relating trace points to gpx files

[Etienne]

One thing about this is that there will always be some "bad" trackpoints in
OSM.  If you look at any city centre you'll see that the tracks can be very
scattered.  It's quite common for a GPS to be "off" because it has picked up
a reflected signal from a tall building.

Over time, with many passes along the same street there will eventually be a
strong _average_ scatter of the  trackpoints that will be be a good
approximation to the actual line of a road, but many of the points will be
quite a distance from the line and sometimes a very long distance.  Take a
look at central London if you want to see streets with many thousands of
trackpoints.

As for whether you should cleanup/edit your tracklogs before uploading them
- I've not seen any serious discussion here on that subject, but since the
tracklogs are supposed to represent the raw data from which the refined maps
are created I wonder if its actually a good thing to manually edit them
before uploading?

Etienne

On 7/14/06, Andrew Loughhead <andrew at incanberra.com.au> wrote:
>
> On Fri, 2006-07-14 at 09:59 +0200, Erik Johansson wrote:
> > On 7/14/06, Andrew Loughhead <andrew at incanberra.com.au> wrote:
> > > On Wed, 2006-07-12 at 10:57 +0200, Erik Johansson wrote:
> > > <--snip-->
> > > > A far as I know (from reading the code)  when you delete a GPX file,
> > > > the points will be marked invisible. So they will disappear from the
> > > > rendered images.
> > [...]
> > > I have been able to delete all my files and start loading them
> > > individually, checking each result in JOSM.
> >
> > Oh no... This thing about deleting GPX traces. I don't like it, we
> > should never make people delete the files. I think it's blasphemy to
> > remove data from the traces db.
>
> I have finally found my problem file. As is traditional, it was the last
> file I looked at. I have deleted the 20 odd garbage track points, and
> all data has been re-sent to OSM.  So far the applet display still shows
> the bad points.
>
> I could have found the bad data without deleting files from OSM, if I
> had tried a little harder (or to be honest, actually turned my brain
> on). But it was an effective, if tedious, way of finding where the bad
> points came from.
>
> Andrew.
>
>
>
>
>
> >
> > I also use josm and I do it like this:
> > 1. load GPX file
> > 2. download GPS traces for that area
> > 3. upload GPX file to OSM
> > 4. edit
> >
> >
> > > One question for the list: in JOSM it seems that if raw gps mode is
> used
> > > for an OSM download, that all points in view are treated as being a
> > > single track, based on sequential time stamp?  The result being that
> > > relatively random straight segments appear just because there happen
> to
> > > be some track points in view?  The manual doesn't really say.
> >
> > The traces downloaded from the server are just dots on a map nothing
> > more. As far as I can remmeber they have no metadata.
> >
> > You should always create OSM data layers from a GPX file you yourself
> > have created. Never from traces that is downloaded from the server.
> > And I'm not quite sure why it's not strictly verboten. Imi?
> >
>
>
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