So we can better distinguish initial position from small islands on
the map.

This is useful for hacking.

The downside is that we store all duration values.

Test `args.min_duration` outside the loop on `expanded_traj`. Clearer.

Invert order of dummy arguments orientation and layer of method
`get_reader`. Take the same order than in the path. `orientation` was at
the end because, at first, in commit d858fb72, it was an optional
argument.

On second thought, I find the default value confusing. We are
reverting commit b328ab6f.

Otherwise we can have a line across the globe between two points with
longitudes close to -180° and 180°.

Simpler because that is what the plot command needs.

Because we are going to define a function.

For reproducibility.

Because we are going to add an optional argument.