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:

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

Best regards,


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igotu2gpx Edit question
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Solved by:
Michael Hofmann
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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
( 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
(, 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!).<email address hidden>&forum_name=gpsbabel-misc

Henrik (neu242) said : #5

Thanks Michael Hofmann, that solved my question.