ghsim

Bullet simulation for Rhino Grasshopper.

Installation

1. Install python 3.6 or higher on your system. The newest version of python can be obtained from https://www.python.org/downloads/.

2. Install dependencies for the simulation server.
   pip install numpy scipy

3. Install the PyBullet simulator. This can be achieved by opening the terminal and typing
   pip install pybullet
   However, this will install the upstream version of PyBullet which currently limits the number of meshes of a single physical object to 16. If this is not sufficient for you, you can install our fork instead, which increases the limit to 32:

   1. Download the sources from https://github.com/TimSchneider42/bullet3/archive/d3c152d77f30ffc837be36710563d6dede01fb56.zip
   2. Unpack the sources.
   3. Run pip install /path/to/unpacked/sources

4. Install the ghsim Grasshopper plugin.

   1. Open Grasshopper and click on File > Special Folders > Components Folder
   2. Copy the ghsim folder (the directory containing ghsim.py, not the entire repository) into the directory that just opened. In the components folder of Grasshopper should afterwards be a directory ghsim containing only a single file ghsim.py.
   3. Again in Grasshopper, click File > Special Folders > User Objects
   4. Copy the content (!) of the user_components directory into the directory that just opened.

   You should now see a category ghsim as soon as you restart Rhino/Grasshopper.

Usage

Before the simulation can begin, the simulation server needs to be started. This can be achieved by opening a terminal, navigating to the source root of this repository and typing

python simulation_server.py

For a list of options, type

python simulation_server.py -h

As soon as the server outputs Listening on port 8000..., it is ready to process simulation requests.

ghsim comes with 6 types of Grasshopper components, that are briefly explained here:

• PhysicalObjectType: Creates a type of physical object that can appear multiple times at different locations in the scene. Each type consists of a one or more convex geometric shapes that remain in static formation during simulation, and dynamic properties, like the mass or friction coefficients.
• PhysicalObject: Creates an instance of a physical object type. Each physical object consists of the respective object type and a transformation specifying its location.
• ExternalSimulator: Specifies hostname and port of the simulation server.
• Simulation: Executes the simulation given a list of physical objects and some simulation parameters. For further information on the simulation parameters, please refer to the documentation of this component. Outputs a simulation result object for each time step of the simulation.
• SimulationStateAt: Extracts the transformation of each physical object at a specific time from the simulator output.
• UnpackPhysicalObject: Unpacks a physical object into its convex geometries and its transformation.

For usage examples, please refer to boxes.gh and wasp.gh.

Simulation Advice

Ensure that any objects in the scene are not too close together at the beginning of the simulation. Otherwise they might start to overlap which makes the simulation unstable. Instead, always leave 1-2mm distance between objects and rather let them settle during the simulation.