MechanismGeometries

This package implements several methods of generating or loading geometries associated with a RigidBodyDynamics.jl Mechanism in Julia. It is currently used by MeshCatMechanisms.jl but can also be used independently.

Interface

This package exports one primary method:

visual_elements(mechanism::Mechanism, source::AbstractGeometrySource)

visual_elements returns a vector of VisualElement structs, each of which contains:

• frame: A CartesianFrame3D indicating where the geometry is attached in the mechanism
• geometry: One of the GeometryBasics.jl types
• color: an RGBA color from ColorTypes.jl
• transform: a Transformation from CoordinateTransformations.jl indicating the pose of the geometry w.r.t its attached frame.

Currently implemented sources

These demonstrations use the Boston Dynamics Atlas robot from AtlasRobot.jl.

using AtlasRobot
using MechanismGeometries
mechanism = AtlasRobot.mechanism()

Skeleton

Skeleton <: AbstractGeometrySource

The Skeleton type uses only the joints and bodies in the mechanism itself to construct a visual representation of the robot's links. The sticks connect joints in the mechanism and the ellipsoids represent the mass and moment of inertia of each body:

visual_elements(mechanism, Skeleton())

The moment of inertia ellipsoids can also be turned off, leaving just the joint connections:

visual_elements(mechanism, Skeleton(inertias=false))

URDF Visuals

URDFVisuals <: AbstractGeometrySource

The URDFVisuals type loads the visual elements from a given URDF file (passed as either a filename or a parsed XMLDocument from LightXML.jl). One particularly useful argument is package_path, which accepts a list of strings to use as potential directories to search when encountering mesh files using the ROS package:// syntax.

visual_elements(mechanism,
                URDFVisuals(AtlasRobot.urdfpath(),
                            package_path=[AtlasRobot.packagepath()]))

URDF Extensions

The following extensions to the URDF spec are parsed by MechanismGeometries.jl:

• <plane normal="0 0 1"/>: Represents an infinite plane perpendicular to the normal given as an x y z unit vector. Returns a MechanismGeometries.HyperPlane