Reserved key for streamline seed point?

[Lestropie]

With MRtrix3 there's been a few requests over the years to have, for streamlines propagated bidirectionally from the seed point, knowledge of which vertex in the output streamline corresponds to the seed location. See e.g. tckmap -output_seeds option (which was at the time the easiest hack to satisfy demands).

In the context of this format, it's a DPS of either a uintX index or a 3.floatXX, depending on whether the seed point itself or an index in the output streamline is provided (theoretically it's possible that in some implementation the precise seed location won't actually be included in the output streamline; in MRtrix3 we guarantee that it's included, but I'm thinking of the most general case).

Primarily the question is whether or not such information should have some form of reserved keyword so that all implementations know where to write it in order to be trivially accessible / interpretable at read time.

[frheault]

I agree we could have a list of reserved keywords, but it should also come with a small description and specification.
Seeds are definitively on my list too. It would be interesting to see what comes up.

If people have suggestions (and descriptions of use-case) please add it here
https://docs.google.com/document/d/1EVc8n8v6KBgdM31ezHeewYgZLrmun0qKqNRlueQM2aE/edit?usp=sharing