lamm-mit/lsystem-executor

L-System Executor

Execute parametric L-system grammars and render the results as images or meshes.

Overview

Takes a grammar definition (axiom + rewrite rules) and produces:

• Step-by-step derivation showing the string at each iteration
• 2D turtle-graphics rendering as SVG and PNG
• Optional 3D extrusion to STL (if --stl flag is passed)

Useful for investigations that produce symbolic growth grammars (urban evolution, microstructure growth, biological branching) and need a concrete visual artifact.

Usage

From a JSON grammar file:

python3 {baseDir}/scripts/lsystem_render.py --grammar grammar.json --steps 4 --output output_dir/

Inline grammar:

python3 {baseDir}/scripts/lsystem_render.py \
  --axiom "A" \
  --rules '{"A": "A[+B]A[-B]A", "B": "BB"}' \
  --angle 25 \
  --steps 4 \
  --output output_dir/

With STL export:

python3 {baseDir}/scripts/lsystem_render.py \
  --grammar grammar.json \
  --steps 3 \
  --stl \
  --output output_dir/

Grammar JSON Format

{
  "axiom": "A",
  "rules": {
    "A": "A[+B]A[-B]A",
    "B": "BB"
  },
  "angle": 25.0,
  "step_length": 10.0,
  "length_scale": 1.0,
  "title": "Urban-Material Growth Grammar"
}

Symbols

| Symbol | Meaning | |--------|---------| | F | Move forward, drawing a line | | A-Z (uppercase) | Move forward, drawing a line (also rewritable) | | f | Move forward without drawing | | + | Turn left by angle | | - | Turn right by angle | | [ | Push position and heading onto stack | | ] | Pop position and heading from stack | | ! | Decrease line width | | > | Multiply step length by length_scale |

Outputs

The script produces in the output directory:

• derivation.txt — string at each step
• render.svg — vector graphics of the final structure
• render.png — rasterized version (300 DPI)
• render_steps.png — grid showing each derivation step side by side
• grammar.json — the grammar used (for reproducibility)
• render.stl — 3D mesh (only if --stl flag is used)