- advect points, transform from / to
- convert path to directed segments
- undirected segments as a plot
- directed segments (arrows) as a plot
- restoring a path from undirected segments
- restoring a path from directed segments


Graphics wise and aesthetics wise we always end up with the explicit form, so separate the set of edges as identifiers (possibly ordered) from the
functions that get their vertex ids and then their coordinates completely.

Do we want:

get_x0y0_from_edge
get_x1y1_from_edge

segments(x0y0, x1y1)