PyElastica to Rhino

The package is in alpha-phase dev-stage.

PyElastica extension and Rhino plugin for Cosserat Rod (+ Rigid Body) visualization.

Requirements

The Grasshopper plugin does not have any additional requirement, but we recommend using anemone together. This plugin provide loop function that can be used to generate animated video.

Grasshopper Plugin

• PyElastica exports npz file which can directly be imported using NpzImport module.
  • For now, NpzImport(Legacy) is used. More generalized version is still under development.
• Provides CosseratRod and CosseratRodPeriodic that constructs rods directly.
  • Shape of position: (num_rod, timesteps, 3, num_nodes)
  • Shape of radius: (num_rod, timesteps, 3, num_elements)
  • If periodic is set to true, the trapazoidal averaging step is skipped for the radius.
• All modules include C (switch) input. The purpose is to serialize the execution.
• All modules include D (debug) output which returns the debugging text to inform progression or runtime error.

Legacy Import Mode

The grasshopper module import npz file. In the legacy import module, we expect the npz file to have the key <group>_position_history and <group>_radius_history for each group.

• <group>_position_history should have the shape <number of rod, timesteps, 3 (dimension), number of nodes>.
• <group>_radius_history should have the shape <number of rod, timesteps, number of elements>.

The number of nodes is expected to be one more than the number of elements. If the periodic is set to True, the number of nodes can be equal to the number of elements.

For sphere, the number of elements and the number of nodes are both 1. In such case, a sphere module must be used in grasshopper.

PyElastica Extension

We provide a data collector extension to PyElastica to easily collect the batch of data.

pip install elastica-rhino

Example Usage

import elastica
import elastica_rhino as er

... <simulation setup>

data_collector = er.RhinoExportCollector(
    save_path="data",
    step_skip=int((1/fps)/dt)  # Collect data every 'step_skip' iteration 
)
for arm in arm_list:
    simulation.collect_diagnostics(arm).using(
        er.ExportGeometry,
        data_collector,
        group="arm"
)
for muscle in muscle_list:
    simulation.collect_diagnostics(muscle).using(
        er.ExportGeometry,
        data_collector,
        group="muscle"
)

... <simulation setup>

simulation.finalize()

... <simulation run>

data_collector.save()

In Rhino, objects in the same group will be collected by layers. We recommend setting the parameter group for the same material or color of the rods.

Included Callbacks

• ExportGeometry
• ExportStrain (work in progress)
• ExportInternalStress (work in progress)
• ExportExternalStress (work in progress)