it could be done in pd using datastructures - but for that you should ask
to the people who know how to work with them.

I don't know if eg. Processing might have some modules for that. I know
that you can do that with some csound compositional assistance programs
(blue? cecilia? look in csounds.com). they export for text, because csound
works with text - but then the information has to be "converted" to pd
format (which shouldn't be hard to do).

I would advise to stay in pd, unless the gui part is really important. in
that case maybe processing, but I'm making up as I go now. better ask some
of the pros here, who also know all about data structures.

Well, something like this:

Create and move freely the points that form the "broken line" (even
though it looks smooth) with the mouse by clicking in a nice GUI with many
visual and data handling options and functions (zoom, colors, cut-copy-paste,
undo are just a few that come to my mind rapidly).

Also with the mouse, set the smoothness factor of each point (that would affect the concavity of the adjacent lines).

By double clicking in a point, an exact value of coordinates could be entered by text.

In addition, it could have a text-based-point-creation control panel,
where could be set the coordinates where the point will be created.

Finally, a "export to text file" function with selectable resolution.
(May be a "send to PD + "arrayname"" would be ok too)

This is what comes to my mind. May be it's too much. Should I try to
build this in PD or I should use another language? In that case, which one?