Edit therion th2 files directly from tunnel

[goatchurchprime]

It would be desirable to enable the tunnel editor to integrate directly with therion sketch files to give people who use that system a choice of editors.

Tunnel can output SVG, which can be converted to th2 using this satisfyingly simple script. http://www.cavediving.de/svg2th2.py

What I need is:

1. some brief documentation of the th2 file format

2. a real-world example of a set of th2 files (the entire project), pointing out some th2 files in question (including background underlays).

A very good outcome would be if I could just load th2 files into a sketch object as though it were a sketch-xml file (mapping over all the types consistently), and then be able to edit and save back to th2 format readable by therion without any loss of data.

If this gets anywhere we could look into invoking the therion executables from java, like I do with survex.