Currently I`m trying to implement pathfinding to my game,
and currently NavMesh looks like good candidate.

Becouse I don`t wont to create new meshformat for navmesh
I try to use existing ones. (no custom import/export plugins)

So the big question:
Is half-edge mesh data structure + ".ply" file format good for this purpose?

/Tyrian

IMX, for operations on navmeshes you typically need basic connectivity information such as the edges and triangles neighboring each triangle, and the triangles neighboring each edge. The half-edge structure should give you that, so I don't see why it wouldn't be suitable. (I can't think of any reasons off the top of my head at least.)