# Grasshopper 3D
*Expanding Your Parametric Design Toolkit*

## Parametric Design in Grasshopper

**What is parametric design?**

A method where you define relationships between design elements using rules (parameters). Change one input, and the entire design updates automatically.

### Grasshopper Examples

The images below show parametric patterns and structures created with Grasshopper:



These examples are from the **[Mode Lab Grasshopper Primer (PDF)](https://aae280.wordpress.com/wp-content/uploads/2014/10/mode-lab-grasshopper-primer-third-edition.pdf)** (Page 11) – a foundational guide for beginners.

### Example: Physics with Kangaroo
**What is Kangaroo?**
A plugin that adds real-time physics simulations to Grasshopper (e.g., gravity, tension, collisions).
*Why use it?* To create dynamic structures like tensile membranes or bending beams.
- **Tutorial**: [Kangaroo Tensile Structure Tutorial](https://www.youtube.com/watch?v=Sk-beAQb2Mc)

## Example: Loft

**How Grasshopper improves on Rhino’s "Record History"**

In Rhino, if you loft curves and later edit them, you must redo the loft. Grasshopper automates this:
1. Draw curves in Rhino
2. Loft them in Grasshopper
3. Edit curves → Grasshopper updates the loft automatically

## Opening Grasshopper
Type `Grasshopper` in Rhino’s command line to open the visual programming interface.

### Input: Parameters
**What are parameters?**
Components that reference geometry or data from Rhino (e.g., curves, points, numbers).
- **Types matter**: Grasshopper distinguishes between *points*, *curves*, *surfaces*, etc. Mismatched types cause errors!

## Data Flow
**How components communicate**
- **Wires**: Connect components to pass data (left = input, right = output).
- **Add/Delete Connections**: Click+drag to create wires; Cmd (or Ctrl) + drag to remove them.
- **Naming**: Right-click components → Type to label them (e.g., "Base of prism").

### Naming Components / parameters

Right click on the component

### Toggling names/icons

"View" menu

## Plugins

### Food4Rhino

A repository for Grasshopper plugins, scripts, and resources:

[Food4Rhino Website](https://www.food4rhino.com/)

### Installing Plugins

1. Download `.gha` files from Food4Rhino.
3. Place them in Grasshopper’s **Components Folder**:
`File → Special Folders → Components Folder`
[Installation Guide](https://www.food4rhino.com/en/faq#users-install-grasshopper-plugin)

There's also a `PackageManager` in Rhino, but it's a bit of a crapshoot.

### Bifocals

Great plugin for clarity.

## Key Components

### Panel
Displays raw data flowing through your script. Use it to debug or inspect values.

## Example: Divide Curves
1. Draw two curves in Rhino.
2. Use `Divide Curve` to split them into points.
3. Connect corresponding points with lines.

*Result*: A parametric “ribbon” structure.

### Baking

Right-click the final output → `Bake` to turn Grasshopper geometry into Rhino objects.

## Example: Polygon Array

**Step-by-Step**

**Polygon Component**: Define a polygon with sliders for radius (`R`), sides (`N`), etc.

### Inputs: sliders

R / N / E / O


### Boundary Surface

Creates a surface from edge curves

### Extrusion / cap

Just like our old Rhino friends

### Rectangular Array

Duplicate shapes in a grid.
- `Cell` input: Defines spacing between copies (requires a *Rectangle*).

## Organizing our Grasshopper Definitions

### Grouping & Preview

- **Group Components**: Select components → Right-click → `Group` (name groups for clarity).
- **Toggle Preview**: Use the eye icon (top-right) to hide/show geometry.

### Radial Menu

Center click the canvas for quick access to tools.

## Attractors

A concept commonly used in parametric design is that of *attractors*".

These are points or curves that influence geometry (e.g., scaling objects based on distance).

### Scaling with Distance

Use `Curve Closest Point` to measure distances to an attractor curve.

There are other "closest components": `pull point`, etc.

### Fine tuning with arithmetic

Division, multiplication...

Let's do a square root or a logarithm.

We can also use `Graph Mapper` to non-linearly map distances to scaling factors.

## Exercise

Copy and modify the definition so that it's the distance to a curve, not a point, what determines scaling.

## Exercise

Copy and modify the definition from the previous exercise so that the distance to the curve determines rotation rather than scaling.

Modify it also so that its input is a single curve going mostly up in the z axis.

Hint: look up the `sweep1` component.

To give you an idea, this is the sort of thing that we're after:


## Example: The press-fit kit

Examples in [Fab Lab Barcelona local docs](https://fablabbcn-projects.gitlab.io/learning/educational-docs/fabacademy/classes/03-Computer-controlledCutting/#grasshopper).

### Opening Linked Files
Grasshopper files (`.gh`) are separate from Rhino files (`.3dm`). To edit:
1. Open the Rhino file.
2. Open Grasshopper from Rhino.
3. Open the Grasshopper file → It will reference the Rhino geometry.

## Advanced Concepts
### Data Trees
- **Flattening**: Simplifies nested data (e.g., merging lists).
- **Grafting**: Preserves data structure (e.g., keeping branches separate).

## References
- **Grasshopper Basics**: [Grasshopper3D.com](https://www.grasshopper3d.com/)
- **Parametric Bench Tutorial**: [Parametric House](https://parametrichouse.com/parametric/parametric-bench-2/)
- **Plugin Hub**: [Food4Rhino](https://www.food4rhino.com/)
- **Grasshopper Kangaroo Tutorial** [Tensile Structure](https://www.youtube.com/watch?v=Sk-beAQb2Mc)
- **The Mode Lab's** [Grasshopper Primer](https://aae280.wordpress.com/wp-content/uploads/2014/10/mode-lab-grasshopper-primer-third-edition.pdf) (pdf)