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Step 2 — Block Geometry Generation

Script prefix: X20
Session inputs: session["params"], session["refmesh"] (if TNA was run)
Session outputs: session["block_meshes"], session["block_frames"]

Purpose

The geometry step discretises the vault surface into a grid of voussoir block meshes. It takes the equilibrium surface from the TNA step (or an analytically defined geometry for simpler cases) and produces a list of compas.geometry.Mesh objects — one per block — along with their reference frames.

These meshes are the physical geometry of the voussoirs: their faces are the contact surfaces that will be detected and analysed in the DEM step.

Template classes

The geometry generation is handled by template classes that parameterise the block layout and cutting strategy. Each template takes a RefMesh (or equivalent analytic geometry) and a set of block count / thickness / stagger parameters and returns the discretised block grid.

Template Used in Description
FlatBarrelTemplate Examples 200–500 Rectangular grid of voussoirs fitted to a barrel vault RefMesh; block faces are flat (planar cuts)
ArchTemplate Example 100 Parametric semicircular arch voussoirs; no RefMesh needed

Additional template variants are available for different vault profiles (see Templates API).

Code walkthrough — FlatBarrelTemplate

from carbcomn.datastructures import RefMesh
from carbcomn.templates.barrel import FlatBarrelTemplate

refmesh: RefMesh = session["refmesh"]

template = FlatBarrelTemplate.from_spacing(
    refmesh=refmesh,
    voussoirs_count_span=20,    # number of blocks along the span direction
    voussoirs_count_length=7,   # number of blocks along the vault length
    thickness=0.3,              # voussoir thickness [m]
    stagger_type="running",     # "none" | "running"
    stagger_amount=0.2,         # fractional column offset (0–1)
)

block_meshes = template.blocks         # list[list[Mesh]] — [col][row]
block_frames = template.block_frames   # list[list[Frame]]

The output is a two-dimensional list indexed by [column][row]:

  • block_meshes[i][j] — the mesh of the block in column i, row j
  • block_frames[i][j] — the reference frame of that block (origin at centroid, axes aligned with the block's local coordinate system)

Stagger patterns

The stagger_type parameter controls how adjacent vault columns are offset relative to each other:

stagger_type Description Used in
"none" No offset — all block joints are aligned across columns Example 200
"running" Each column is offset by stagger_amount × block length Examples 300–500

Running bond stagger (analogous to brick bonding) improves the structural interlocking between adjacent vault columns and is the intended configuration for the CARBCOMN floor system.

Floor height extraction

After generating the block grid, the template computes the overall floor height from the geometry:

z_max = template.flat_top_z      # highest point of the block extrados
z_min = template.bot_min_z       # lowest point of the block intrados

session["params"]["floor"]["z_max"] = z_max
session["params"]["floor"]["z_min"] = z_min
session["params"]["floor"]["final_height"] = z_max - z_min

These values are written back into params so they are available to downstream scripts (e.g. for frame sizing in the structural grid step).

Export to session

session["block_meshes"] = block_meshes
session["block_frames"] = block_frames
session.sync()

See also: Step 3 — RefBlock & Element Typing, Templates API, Example 200