Extending ops-post

Adding a new element type

Adding an element to ELEMENT_REGISTRY in ops_elements.py is the only change needed. The registry drives TCL parsing, mesh building, and result processing automatically.

Step 1: If the element fits an existing topology

Just add it to ELEMENT_REGISTRY:

"MyNewShellQ4": _Q4,

This gives it Q4 shape functions, 2x2 Gauss points, 4-node surface parsing, and Q4 extrapolation.

Step 2: If it needs a new topology

Define the GP coordinates, shape functions, and extrapolation matrix, then create a new ElemInfo:

GP_TRI_6 = np.array([...])  # natural coordinates

def shape_t6(xi, eta):
    """6-node triangle shape functions."""
    ...
    return N  # (6,) array

_T6 = ElemInfo(
    family=ElemFamily.SHELL_TRI,
    num_nodes=6, num_gp=3,
    gp_coords=GP_TRI_3,
    shape_fn=shape_t6,
    extrap_fn=None,
    face_nodes=[0, 1, 2, 3, 4, 5],
)

ELEMENT_REGISTRY["MyTriElement"] = _T6

What happens automatically

Once the element is in the registry:

System	Behavior
TCL parser	Uses ElemFamily to pick the right parser (surface, beam, truss, zero-length) and reads the correct number of nodes
Postdata generator	Computes local axes from -local, geomTransf, or -orient flags
Mesh builder	Builds surface faces, extrusion, fiber edges, and GP cloud using the registry's shape functions and GP coordinates
Result processor	Uses the registry's extrapolation matrix for GP-to-node mapping

Adding beam inline property extraction

If a new beam type has inline section properties in a different argument layout, add it to _BEAM_INLINE_PROPS in tcl_parser.py:

_BEAM_INLINE_PROPS = {
    "Timoshenko":        (7, 9, 10),   # A at token[7], Iy at [9], Iz at [10]
    "elasticBeamColumn": (5, 9, 10),
    "myNewBeam":         (6, 8, 9),    # new
}

Adding a new result type

Nodal results are auto-discovered from RESULTS/ON_NODES/ in the HDF5 file. Element results are auto-discovered from RESULTS/ON_ELEMENTS/.

To customize component labels for a new nodal result, add it to NODAL_COMPONENTS in result_processor.py:

NODAL_COMPONENTS = {
    "DISPLACEMENT": ["Ux", "Uy", "Uz", "|U|"],
    "REACTION_FORCE": ["Fx", "Fy", "Fz", "|F|"],
    "VELOCITY": ["Vx", "Vy", "Vz", "|V|"],  # new
}

Element result component names are read from the HDF5 META/COMPONENTS field automatically.

Adding a new derived quantity

To add a derived scalar (like von Mises), modify result_processor.py:

1. Add the name to the component list in get_available_results():

   if sg0.num_components >= 6:
       comps.append("Tresca")
   

2. Handle it in _extract_gp_fiber_component() and extract_element_result_for_gp_cloud(), using the component index to detect when the derived quantity is selected (index >= n_comp).

Adding a new visualization layer

1. Build the mesh in MeshBuilder (e.g. build_my_layer()).

2. In MainWindow.__init__, call the builder and store the base mesh.

3. In _full_rebuild, add it with add_mesh(...) and store in self._meshes["my_layer"] / self._actors["my_layer"].

4. In _fast_update, update its .points[:] from the base + displacement.

5. Add a visibility checkbox in the Results tab display options if needed.

Customizing the View tab

The View tab in gui.py contains camera presets and figure controls. Key points for extension:

• GP zero mode: controlled by a dropdown in the Figure section of the View tab. To add a new zero mode, update the dropdown items and the sphere radius calculation in result_processor.py.
• Scale range clamping: min/max spinboxes in the Figure section. To add more clamping options, extend the spinbox layout and the scalar array clamping logic in _apply_scale_range().
• All settings apply immediately: there is no Apply button. Connect new controls to their update methods directly (e.g. spinbox.valueChanged.connect(self._full_rebuild)).

Customizing interaction

The arcball interactor is in utils.py (ArcballInteractorStyle). It uses the Shoemake arcball algorithm:

• Mouse positions are projected onto a virtual unit sphere.
• A single rotation is computed from drag-start to current position.
• The rotation is applied to the saved initial camera state (no drift).

To change the rotation pivot from world origin to another point, modify _arcball_rotate() to rotate around a different center.

To add left-click pick/inspect, implement _on_left_press and use VTK's cell picker to identify the clicked element.