Number of nodes.
Centre of the crown envelope; leaf normals point away from it.
Parent node index, or -1 for the root. Parents always come before their children.
xyz per node, metres; the base of the trunk is at the origin.
Branch radius at each node (pipe model).
Steps from each node to its nearest branch tip (0 = a tip).
Number of branch tips above each node.
A grown branching structure: nodes connected to their parents, with pipe-model radii.