Glossary

Terms specific to Natsura, and the botanical terms used in the docs. Standard Houdini and game engine terms aren't covered here.

Natsura terms

Assembly: a prefabricated branch, leaf cluster or similar part, rigged and made of instanced pieces, placed on a tree by the Assembly Decoration. See Assembly Workflow.

Assembly library: a set of assemblies prepared by an Assembly Resource, or made from a simulated branch by Rig to Assembly, for an Assembly Decoration to place.

Decoration: a meshing process you assign to a Grow, which meshes the part of the tree that Grow makes. Decorations run inside the Simulate, after the skeleton has grown. See Decorations.

Effector: a direction on the growing skeleton, such as gravity, that a Grow or an Assembly Decoration reads through a mode to steer growth or pose parts. See Effectors.

Generation: one step of the simulation. The generation attribute is the step a point was created on, and age is how many generations it has existed.

Graft: the join between a scanned trunk and the procedural growth that extends it. See Create Graft Mesh.

Internode: the length of stem one growth step makes, and the unit a Natsura tree is built from. Each internode carries attributes that maps, switches and decorations read; they are listed on the Wrangle page.

Map: a node that computes a value for each point from an attribute, so a parameter can change across the tree. Chains of maps can be combined. See Mapping.

Module: a node built from the core verbs that describes a whole growth behaviour. Grow is the first module: a repeat, a switch and a split with an interface for artists. See Simulation.

Profile: an open end of a scanned trunk that procedural growth extends from. See Scan Profiles.

Recipe: the graph of growth nodes, maps, effectors and decorations that describes a plant. It goes into a Simulate, which grows it.

Simulate: the node that runs the recipe and outputs the tree, skinned and rigged. Every Natsura graph ends in one. See Simulate.

Skeleton: the curves the simulation grows, before any meshing. Set Output to Skeleton on the display toolbar to see it.

Spawn point: a place on the skeleton where the Assembly Decoration puts a part: a tip, an intersection, an internode or a root.

Trait: an attribute that lives both on the parts in a library and on the skeleton, such as age or size. The Assembly Decoration matches them to decide which part goes where. See Trait System.

u: a gradient along each branch from 0 at its base, reaching 1 at the tip once the branch is fully grown (u_normalized reaches 1 at the tip of a branch still growing). It is the attribute maps read most often.

Verbs: the core operations the growth grammar is made of: grow, split, switch and repeat. The artist-facing growth nodes are built on them. See Internal Nodes.

Wrangle: a growth node that runs your own VEX on the growing tips. See Wrangle.

Effector modes

A Grow reads each effector in its stack through one of these modes: Attract, Repel, Flatten (at a plane to the direction), Orbit (around it, in a spiral), Align (up) and Level (up). Align (up) and Level (up) turn the up vector of the growth toward the direction or level with it, which changes the spiral and so how shoots are arranged around the stem. The Assembly Decoration lists the same modes except Orbit. See Effectors.

Botanical terms

Apical dominance: how strongly the leading shoot holds back the side shoots below it. Strong apical dominance gives a single straight leader, as in many conifers; weak apical dominance gives a spreading, much-branched crown, as in many broadleaves.

Bifurcation: a fork, where one axis divides into two of about equal strength. On a Grow, Enable Forks makes the chain fork as it grows.

Bole: the main trunk of a tree, from the ground to the first large branches.

Crown: the branches and foliage above the trunk. Its silhouette and density are what most shaping work aims at.

Monopodial and sympodial: a monopodial stem keeps growing from the same tip, so the tree keeps one leader; in a sympodial one the tip stops and a side shoot takes over, so the stem is a chain of forks. The Assembly Decoration's preview offers both kinds of tree.

Phyllotaxy: the arrangement of shoots or leaves around a stem. Common patterns are alternate-spiral (one per node, each turned by a fixed angle, often about 137.5°), opposite (two per node, each pair turned 90° from the last) and whorled (three or more per node). On a Grow, Spiral Angle° (Start > Phyllotaxy) swings each shoot around its parent stem, Multiplicity sets how many start at a node, Whorl Angle° spaces them around the stem, and ΔRoll °/step (137.5° by default) turns each step.

Senescence: the decline phase of a tree's life, including a shrinking crown and dead wood kept on the tree.

Thigmomorphogenesis: the change in a plant's form under mechanical stress such as wind or contact, which gives the shorter, stockier and often one-sided trees of exposed sites.

Tropism: growth toward or away from something: light (phototropism), gravity (gravitropism) or contact (thigmotropism). In Natsura, effectors produce tropisms. With an environment wired into the Simulate's Geometry input, a Grow can add Photo Direction (toward or away from light) and Thigmo Direction (the direction to the nearest surface) as effectors.

Whorl: three or more shoots starting from one node, spaced around the stem. On a Grow, set Multiplicity to 3 or more.

For how these fit together, start with the Overview.