Machinery TwinCoordinates & units
World space, model space, and the units used across the app.
Two spaces per object
Every object has two independent poses, edited in different sections of the Objects panel:
| What it moves | When to use it | |
|---|---|---|
| World pose | The object itself (and its kinematics) in the scene | Placing the machine part where it belongs |
| Model pose | The 3D model relative to the object's origin | Aligning imported CAD to the object's mathematical origin |
The distinction matters most for mechanisms: a crank's kinematic solution rotates about the object's origin. If the imported CAD isn't modelled about that same point, you correct it with the model pose, offsetting and rotating the geometry until it sits correctly on its joint, while the world pose stays the clean, meaningful location of the mechanism.
Both poses use the project's selected up-axis convention. In a Z-up project, the Z field and the blue Z gizmo handle point upward for world pose and model pose alike. Imported glTF geometry remains Y-up internally; that asset detail is converted at the renderer boundary and does not leak into project coordinates.
Mechanism objects (cranks, linkages, arms) repeat this per link: each link has its own model with its own model-space offset.
Rotations
Rotations are entered in degrees, as XYZ Euler angles. Mechanism inputs (crank angles, revolute joint values) are degrees as well.
Lengths
Lengths (link lengths, path segments, DH parameters d and a) are in scene units. Keep one convention project-wide, so if your CAD is in millimetres, treat one scene unit as one millimetre and import models with the scale selector that matches. Mixing conventions between the CAD scale and the kinematic dimensions is the most common cause of "the model flies away" surprises.
Hierarchies
A child object's pose is relative to its parent. Attaching an object to a mechanism's link puts it in that link's frame, so it inherits all the link's motion. See Hierarchy & attachments.
Robot arm frames
Serial manipulators add one more frame subtlety: DH parameters define joint frames following the DH convention (Z along the joint axis), which usually differs from the world's "up". The Serial manipulator page covers base orientation and the global-vs-local workspace frame toggle.