[Gpsbabel-misc] extreme simplification

[Vidar G. <vid...@37...>]

I was playing with the idea of using the simplify filter to
place one waypoint on a map for each tracklog, to create
an inventory of a large amount of tracklogs, which can be
used to speed up filtering of files using the polygon or
radius filters.


Trying this, the following are achieved:

  -x simplify,count=1   Last location
  -x simplify,count=2   First and last location
  -x simplify,count=3   First, middle and last location

What is the middle point?
Is it where half the distance was travelled,
or the halftime position?

  -x simplify,count=4   Adds halfway to middle location?
  -x simplify,count=5   Adds middle of first quarter?
  -x simplify,count=6   Adds middle of second half?

Is this correctly observed?


Let's say that the GPS unit typically starts logging before
a good 3d fix have been achieved (mine does, and this will
affect the results from the above filtering), so I'd like to
be able to offset the start of each tracklog by a certain
sample count, or a given time interval. This is similar to
the "-x track,start=" filter, only the time is relative, e.g.:

  -x track,start=+30s


Back to my above tracklog inventory: I'd like to
create a GPX file with one waypoint for each tracklog,
where the name of each waypoint is the file name of the
original tracklog (where the position should ideally be
a geometric average, but the endpoint is also useful).

This should be feasible using GPSBabel and a bit of shell
scripting (or Perl/Python), I think.