Annotate Modelica Animation

Annotate Modelica 3D Animation

Adds __Wolfram(Animation(...)) annotations to a MultiBody model so Simulation Center opens a configured 3D animation: named cameras, follow cameras, trace paths, playback behavior and vector scaling — all stored in the model file.

Only models using Modelica.Mechanics.MultiBody components with a visual representation get an Animation view. Simulate first (simulate-modelica): you need the trajectory extents to place cameras and size the scene, and a model that fails to simulate has no animation to configure.

Unlike the control-panel, graphics and plots annotators, this skill has no generator engine — you author the annotation text and splice it in by hand, then validate. That puts the merge-into-annotation(...) step (below) on you; get it right and confirm with validate-modelica.

This is a vendor-specific annotation (Modelica spec §18.1): other tools ignore it and preserve it on save, and it does not affect flattening — it only tells System Modeler how to build the 3D animation. It sits directly inside the class annotation(...), as a sibling of experiment and Documentation (never nested inside Documentation).

The annotation

annotation(__Wolfram(Animation(
  cameras = {
    Camera(name = "Follow", distance = 8, rotation = {0.5, 0.5, 0.5, 0.5},
           follow = bodyShape.shape1, followMode = "NODE_CENTER_AND_AZIM"),
    Camera(name = "Top", center = {32, -19, 0}, distance = 90, rotation = {0, 0, 0, 1})},
  windows = {
    Window(name = "Default", camera = "Follow", preferred = true,
           autoPlay = true, repeat = true, timeScale = 0.5,
           trace = {bodyShape.shape1},
           vectorSettings = {VectorSettings(quantity = "Force", scale = 0.1)})})));

Splicing it into the model

The Animation(...) goes inside the single class-level annotation(...), as a sibling of experiment/Documentation — not in its own second annotation.

• No class annotation yet — add one before the terminating end <Class>;:

    annotation(__Wolfram(Animation(...)));
  end MyModel;
  

• An annotation(...) already exists (e.g. experiment) — add __Wolfram as another argument inside it, don't create a second block:

    annotation(
      experiment(StopTime = 10),
      __Wolfram(Animation(...)));
  

• A __Wolfram(...) already exists (e.g. from FMI or a control panel) — add Animation(...) as another argument inside that same __Wolfram(...), rather than a second __Wolfram:

    annotation(__Wolfram(
      FMI(version = "2.0", kind = "ME"),
      Animation(...)));
  

Two annotation(...) blocks on one class, or two __Wolfram(...) inside one annotation, is invalid — merge instead. If the class already carries an Animation(...), edit that one rather than adding a second.

Camera fields

• name, center = {x,y,z}, distance, rotation = {q1,q2,q3,q4} (quaternion). center is ignored when follow is set (a follow camera derives its center from the tracked object), so omit it on follow cameras.
• follow = <cref> attaches the camera to a shape. The cref must be the low-level visualizer instance inside the component (its Visualizers.Advanced.Shape/Arrow/Surface), not the component itself — follow = bodyShape is ignored and the camera stays unattached. That leaf name depends on the component: vis for Visualizers.FixedShape, shape for FixedShape2/Parts.Fixed, shape1 (and shape2 for the CM sphere) for Parts.BodyShape, cylinder/sphere for Parts.Body, sphere for PointMass, arrow for WorldForce/SignalArrow, and a nested path like frameTranslation.shape for BodyBox/BodyCylinder. The reliable way to get the exact cref is to pick the shape in Simulation Center (right-click → Camera Follow Mode, or Trace) and keep the cref it stores.
• followMode: "NODE_CENTER" (Object Center), "NODE_CENTER_AND_AZIM" (Object Center and Azimuth), "NODE_CENTER_ROTATION" (Object Center and Rotation). For fast-spinning bodies avoid NODE_CENTER_ROTATION — the camera spins with the body; NODE_CENTER_AND_AZIM gives a natural chase view.

Window fields

• camera = "<name>", preferred = true (open automatically after the first simulation), autoPlay = true, repeat = true, timeScale = <r>.
• trace = {<cref>, ...} draws trace paths, using the same low-level visualizer crefs as follow above (e.g. bodyShape.shape1, not bodyShape).
• groundGrid = false hides the ground grid. Omit the field to keep the grid: a stored false re-applies every time the window opens, so remove it from the annotation rather than toggling in the viewer.
• vectorSettings = {VectorSettings(quantity = "Force", scale = <m/N>, diameter = <r>)} and defaultVectorDiameter = <r> scale MSL 4.x vector visualizers (e.g. WorldForce arrows).

Quaternion starting points (z-up world)

If the ground renders vertical, the camera's up-axis is wrong — start from one of these and adjust, or set the camera in Simulation Center once ("Add Camera to Model") and keep the numbers it writes.

Workflow

1. Simulate; read the motion extents from the results.

2. Add a ground plane so motion reads against a fixed reference — size it from the simulated extents plus margin, top surface just below the motion floor:

   Modelica.Mechanics.MultiBody.Visualizers.FixedShape ground(
     shapeType = "box", lengthDirection = {1, 0, 0}, widthDirection = {0, 1, 0},
     length = 90, width = 60, height = 0.02, r_shape = {-10, -19, -0.03},
     color = {60, 150, 60});
   connect(world.frame_b, ground.frame_a);
   

3. Add cameras (a follow camera for playback plus fixed top/side views for shareable stills — the window's trace applies to every camera).

4. Add one Window with playback flags and traces; validate the model (validate-modelica) and let the user confirm the view in Simulation Center.

After a user stores anything from Simulation Center's animation dialogs, diff the annotation: a GUI store rewrites the whole Window(...) from the current viewer state, overwriting autoPlay, repeat, timeScale, groundGrid and trace with whatever the viewer happens to show at that moment (e.g. autoPlay becomes whether playback is running, trace becomes the currently traced shapes). So re-apply hand-authored values after a store — do GUI stores first, hand-edits last.

CAD shapes

Attach CAD geometry to FixedShape / BodyShape with shapeType = "modelica://<Library>/Resources/<file>.stl" (ship the file in the library's Resources/ folder). For file shapes, length/width/height act as scale factors (set all three to one scale value), and lengthDirection / widthDirection remap the CAD file's axes into the MultiBody frame.

In Wolfram Language, CreateSystemModel[Import["part.stl"]] (pass the imported mesh, not the path) generates a ready part: a Body with the full inertia tensor computed from the geometry plus a matching FixedShape, with consistent axes and the frame at the center of mass.