Building model

extensions/building/ holds one canonical model of a building. The render view, the structural view, the thermal view and IFC exchange all read it. A Building holds storeys, spaces, elements, openings, materials and constructions over one cell complex.

Coordinates are meters, z up. The x axis points east and the y axis points north, unless Site.north turns true north.

Modules

Module	What it gives
ids	StoreyId, SpaceId, ElementId, OpeningId, FurnishingId, MaterialId and ConstructionId
kinds	ElementKind, OpeningKind, SpaceUse, SectionShape and FurnitureKind
material	BuildingMaterial, Look and the library: concrete, steel, timber, brick, gypsum_board, mineral_wool, glass and aluminum
construction	Construction, Layer, Glazing, FlowDirection and the ISO 6946 film resistances
model	Building, assemble, Site, Storey, Space, Element, Opening, Furnishing, Section, WallFrame, SpacePlan, StoreyPlan, ConstructionSet and quads_apart
fingerprint	fingerprint, a 64-bit hash of the model's content
views/render	add_building, which adds meshes to a scene
ifc	IFC exchange
generate	Floor plans and interiors and procedural towers

Assemble a model

Give the storey plans, the materials, the constructions and the construction for each kind of face. assemble builds the cell complex. It makes one space per plan polygon, one wall element per wall face and one slab or roof element per horizontal face.

var plans = List[StoreyPlan]()
var ground = List[SpacePlan]()
ground.append(SpacePlan("office", OFFICE, [Point2(0, 0), Point2(6, 0), Point2(6, 5), Point2(0, 5)]))
plans.append(StoreyPlan("ground", Length64(3.5, METER), ground^))
var building = assemble(
    "office", site, Length64(0, METER), plans, materials^, constructions^,
    ConstructionSet(exterior, partition, ground_slab, floor, roof),
    Length64(1e-6, METER),
)

Face	Element	Construction
Wall with the outside on one side	WALL	exterior_wall
Wall between two spaces	WALL	interior_wall
Floor of the first storey	SLAB	ground_slab
Floor between two spaces, or under an overhang	SLAB	floor
Face with the outside above it	ROOF	roof

Then add frame members and openings:

Method	Adds
add_column(storey, at, section, material)	A column from the storey's floor to the floor above. Its depth runs along x.
add_beam(storey, start, end, section, material)	A beam whose axis lies at the top of the storey
add_opening(kind, wall, offset, sill, width, height, glazing)	A door or a window in a wall, placed in the wall's frame
add_furnishing(kind, space, center, rotation, width, depth, height)	A piece of furniture: a box on the space's floor

All views check the model before they use it. Validation checks mutable ids, dimensions, required fields and topology maps, as well as opening and furnishing placement. A surface element must have one face, as assemble creates it.

add_opening refuses an opening that does not fit its wall, overlaps another opening, or is a door that does not start at the floor. A window needs a Glazing. Glazing on a door is not supported and is refused. add_furnishing refuses a piece that leaves its space or overlaps another piece in it.

Read the model

Method	Returns
floor_area(space), volume(space)	The area and volume of a space
gross_floor_area()	The sum of the floor areas
space_neighbors(space)	The spaces that share a face with a space
elements_of_space(space)	The walls, slabs and roofs that bound a space
element_of_face(face)	The element on a face of the complex
openings_of(wall)	The doors and windows in a wall
wall_frame(wall)	The wall's base start, its directions and its size
is_exterior(element)	Whether an element has the outside on one side
validate()	Nothing. It raises if a part does not agree with the others.

Materials and constructions

A BuildingMaterial holds a density, an elastic modulus, Poisson's ratio, a strength, a thermal conductivity, a specific heat, a thermal expansion and a Look. A structural solver, a thermal solver and a renderer each read the same material. The library values are typical values from ISO 10456 and the Eurocodes. They are not design values.

A Construction is a list of layers from the outside face to the inside face. u_value(materials, direction) gives the thermal transmittance by ISO 6946. It adds the layer resistances and the two surface films:

Direction	Inside film, m² K/W	Outside film, m² K/W
HORIZONTAL_FLOW, a wall	0.13	0.04
UPWARD_FLOW, a roof	0.10	0.04
DOWNWARD_FLOW, a floor	0.17	0.04

heat_capacity_per_area(materials) gives the heat that one square meter stores per kelvin.

A Glazing is a window unit by the simple glazing model: a U-value, a solar heat gain coefficient and a visible transmittance.

Frame sections

A Section is a rectangle, a doubly symmetric I or a circle. It gives the area, the two second moments of area and Saint-Venant's torsion constant. The torsion constant of a rectangle comes from a series that is within 0.2% of the exact value. The torsion constant of an I adds its plates, b t³ / 3 each.

Render the model

add_building(scene, assets, building, options) adds one node for the building and one mesh per storey and look under it. It returns the node and the counts of meshes and triangles.

Option	Effect
RenderOptions(FULL, -1)	Every element, with doors and windows cut through their walls
RenderOptions(MASSING, -1)	Exterior walls, roofs and exposed slabs only, with flush window panes
RenderOptions(FULL, k)	Storeys up to k only, without the roof of storey k, for a cutaway

Each vertex carries an elementId attribute. It is the element index for an element. It is the opening index plus the element count for a door or window. It is the furnishing index plus the element and opening counts for furniture. Full detail draws each piece of furniture as a few boxes in wood, fabric, ceramic or metal.

The building node's user data records model, fingerprint, detail, topStorey and dropped. A game can compare the fingerprint with the model's fingerprint to tell whether a baked mesh is current. The hash includes names, site, physical properties, looks, glazing, geometry and model maps. It excludes private acceleration caches and the weld tolerance used to assemble or import geometry. This version changes fingerprints made by the earlier incomplete hash.

The model is z up and the scene is y up. A model point (x, y, z) is the scene point (x, z, -y).

Limits

• A wall is drawn centered on its face, and extended by half its thickness at each end. Walls overlap at corners, and the inside layer can show in a thin seam at an outside corner.
• The render view draws a construction's outside and inside layers on the two faces of a wall. It does not draw the layers between them.
• A beam is drawn below its axis. A column is drawn as a box or a cylinder; an I-section is drawn as its bounding box.
• The model has no stairs, ramps, curtain-wall mullions or sloped roofs.
• Element names come from their kind and index. Renaming them changes the fingerprint.

See Why buildings have one canonical model.