Filter faulty waypoints?

Asked by Henrik on 2010-03-28

I've got the i-gotU Travel Logger [1] (aka Mr Lee Cat Track [2]), which
I attach to my cat. The device is great for its size, but it seems to
be logging quite a few wrong waypoints. Unless my cat is able to
teleport and fly, of course.

Here's an example track:
http://www.everytrail.com/view_trip.php?trip_id=237305

Would you be able to suggest how to filter out the faulty waypoints?

Best regards,
Henrik

[1] http://www.a-trip.com/download#IGOTU
[2] http://www.mr-lee-catcam.de/ct_how_en.htm

Question information

Language:
English Edit question
Status:
Solved
For:
igotu2gpx Edit question
Assignee:
No assignee Edit question
Solved by:
Michael Hofmann
Solved:
2010-03-30
Last query:
2010-03-30
Last reply:
2010-03-30
Michael Hofmann (mh21) said : #1

Could you take a look at the output of "igotu2gpx dump --details" and
see whether the number of satellites or the ehpe value give you some
indication whether the trackpoint is a valid one?

Henrik (neu242) said : #2

Thanks a lot! I can see now that the number of satellites varies between 3 and 7, and EHPE varies mostly between 1.4 and 7m (but sometimes as high as 500m). Would it be possible to add a thresholding filter for these values?

Best Michael Hofmann (mh21) said : #3

You can use gpsbabel
(http://www.gpsbabel.org/htmldoc-1.3.6/filter_discard.html) to filter
depending on the number of satellites (which we export to GPX) and
HDOP (which we do not export).

There is a bug report about EHPE as HDOP export
(https://bugs.launchpad.net/igotu2gpx/+bug/484667), and this will be
in the next version. Until then, could you test whether filtering by
the number of satellites helps? For filtering out all points that have
less than 4 satellites: "gpsbabel -i gpx -f in.gpx -x discard,sat=4 -o
gpx -F out.gpx"

Henrik (neu242) said : #4

Thanks again. I actually went further yesterday and implemented a gpsbabel filter that removes waypoints with way-off altitudes. It's in trunk already, thanks to the very friendly and responsive gpsbabel maintainer (thanks, Robert!).

http://sourceforge.net/mailarchive/forum.php?<email address hidden>&forum_name=gpsbabel-misc
http://gpsbabel.cvs.sourceforge.net/viewvc/gpsbabel/gpsbabel/discard.c?r1=1.8&r2=1.9

Henrik (neu242) said : #5

Thanks Michael Hofmann, that solved my question.