Lecture 7

Papers cited on XFrog

(at least the ones in English…)

A modeling method and user interface for creating plants in Graphics interface 1997 and Computer Graphics Forum 1998 (Journal)
Interactive modeling of plants. IEEE computer graphics and applications 1999

summary of chapter

The goal is to combine the intuitive nature of procedural methods with the modeling power of rule-based methods.

plant = combination of components.

components generate leaves, stems or other primitives using procedural methods.

Some components multiply other components (like rules in a rewriting systems) and other components are for "global modeling" (what's that?)

[Luther] I think the global modeling is things like the exceptions (noted on page 93), and the tropisms, pruning, and FFDs (see 9.5)

There's a UI for making this all happen.

One connects component prototypes into a directed graph which specifies how the plant should be drawn. This graph is called a p-graph.

Edges are production dependencies, after the parent node has it's geometry generated, it invodes the gemoetry production for its children until the tree is generated.

An i-graph contains the geometry instances created by walking the p-graph. The i-graph has a different structure because of the multiplication components.

[Luther] If I understand right, p-graph to i-graph is "rule-based" or rather, if I read correctly, rule-like parameterized procedures; i-graph to geometry is (purely?) procedural.

The examples shown later demonstrate that Lintermann and Deussen succeeded in creating a powerful modeling tool. The strength of their approach is that they allow recursion and replication from which systems like L-systems draw their power but they have embedded recursion and replication in a system which admits more intuitive editing through a clear set of parameters. The parameters are set in each node. The user can unroll recursion in the graph to expose parameters at different levels of the branching structure. By exposing these parameters, Lintermann and Deussen have simplified the process of controlling the final shape. Also, encapsulating parameters in objects simplifies the use of parameters compared to the definition and use of parameters as guards and a kind of side-effect in L-systems.

Algorithmic multiplication (6.1)

A node can spawn multiple children so that the p-graph and the i-graph are not equal. This generates several siblings in one generation of the i-graph.

Or a node can recursively generate copies of itself. This generates several generations in the i-graph.

Component types (6.2)

camera: sets the parameters which will be used to view the model.

[Luther] Why is this part of their model at all? Nothing in the geometry effects or is effected by this node, as far as I can tell.

base: all other components are derrived from the base. It can be any geometric primitive. has a parameter for phototropism.

surface of revolution: like a base, but for a curve swept to make a surface. Has a different dialogue, so made it's own component.

leaf

horn
tree
hydra
wreath
phiball
FFD
Hyperpatch
World

[Luther] How do the horn and tree components differ?

Combinations of components (6.3)

child
branch
leaf

Examples (6.4)

see book and papers.

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