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Matter — walls, openings, columns, slabs

A boundary segment is a centre line. Thickness and z land on it and it becomes a wall; openings split the wall; columns rise where a grid intersection meets a floor; floors, ceilings and roofs appear out of what the levels already declared. None of it has a "place it" operation.

Storey pitch — how far walls and columns rise​

The level a boundary stands on is that of "a if a has a region, otherwise b". The bottom of the wall is that level's FL.

Storey pitch is decided like this.

there is a level above : pitch = z of the level above − z of this level
there is none          : pitch = the tallest ceiling height on this storey + ROOF_T (200mm)

Aligning to the apex of the roof when nothing is above is required because the roof is pitched by the same formula. Without it the wall either punches through the roof or leaves a gap beneath it.

If no ceiling height can be determined, neither can the pitch, and no wall and no column stands on that level. SUF01 already says so as an error.

levelPitch(model, level) answers this on its own.

Wall thickness and z range​

ThicknessTop
Wall (type:wall)t: if written, otherwise WALL_T (100mm)FL + pitch
Non-enclosing boundary (air:1)t: if written, capped at RAIL_T_MAX (80mm); otherwise RAIL_T (60mm)FL + the boundary's h:, otherwise RAIL_H (1100mm)

Thickness is distributed half to each side of the centre line. The same holds for a diagonal segment: the quadrilateral is the centre line offset by ±t/2 along the unit normal (thicken).

An type:open boundary has a segment but no matter — FormBoundary.material is absent.

Placing a band — openings and segs​

An opening and a seg are both "an interval on a boundary segment", and both are placed by the same rule. The order matters.

  1. Take the boundary's segments (the boundary's own edge: is already applied). If the band carries edge:, narrow further
  2. No segment at all: it cannot be placed (OPN04 / SEG04)
  3. Two or more segments: a face must be chosen (OPN05 / SEG05)
  4. Band wider than the segment: it cannot be placed (OPN06 / SEG06). Equal is fine
  5. A grid reference (at:X2+450) cannot be used on a diagonal segment; a horizontal segment takes an X grid and a vertical one takes a Y grid (OPN07 / SEG07); running off the end fails (OPN08 / SEG08)
  6. A ratio (at:0.2, default 0.5) is clamped so the centre fits at both ends. No diagnostic is emitted

The centre is taken parametrically from the start of the segment to its end — one formula for axis-parallel and diagonal alike. So if the direction of the segment changed, the same at: would point somewhere else. Segments — derived and drawn alike — always run in ascending coordinate order, so the result depends on neither the a/b order nor the order the line's endpoints were written in.

The z range of an opening​

The head of an opening aligns with the lintel. A door rises from the floor to the head; anything else drops from the head by its own height.

door    : z0 = FL                                     ; z1 = FL + (h ?? OPENING_HEAD)
opening : z0 = FL + OPENING_HEAD − (h ?? OPENING_H)   ; z1 = FL + OPENING_HEAD

OPENING_HEAD is 2000mm, OPENING_H is 1200mm.

Sill height is never written. It falls out of aligning the head. sill is a carried attribute, so core does not read it. window w:2600 h:1100 on a level at FL 0 lands at z 900 to 2000.

{ kind: "window", w: 2600, z0: 900, z1: 2000, t: 150 }

The leaf thickness t equals the wall thickness.

A wall is a list of intervals split by openings​

Openings on a segment are ordered by distance from its start. Between openings a full-height interval remains; at an opening a sill wall (floor up to the bottom of the opening) and a head wall (top of the opening up to the head of the wall) remain. Intervals whose length or height is at or below SPAN_EPS are not produced.

The partition in examples/two-rooms.muro (t:120, door w:780 h:2000, pitch 2600) really splits like this.

panels:
  (3600,0)    → (3600,1860)   z 0 … 2600     full height
  (3600,1860) → (3600,2640)   z 2000 … 2600  head wall
  (3600,2640) → (3600,4500)   z 0 … 2600     full height

A door rises from the floor, so no sill wall appears. A window would produce both.

With this rule, "paint the black band of the wall in the paper colour so it reads as a hole" simply does not exist as an operation. In plan and in solid alike, the wall is a list of intervals that already has the hole in it.

Where a door opens, and its trace​

The side it opens into is swing:a/b, or, unwritten, "a if a has a region, otherwise b".

The direction is decided by the component pointing at the centre of the bounding box of the derived piece nearest the opening, on the side it opens into. It reads shape, not allocation — in a space cut by a drawn line, the centre of the nearest allocation can land on the wrong side of the line.

The hinge is decided like this.

SegmentHinge
horizontaleast end with hinge:E, west end otherwise
verticalnorth end with hinge:N, south end otherwise
diagonalpinned to the start point. hinge's N/E/S/W are words about axes and do not apply to a diagonal

The trace is a quarter circle centred on the hinge with radius equal to the opening width, sweeping from the leaf tip (the opening width from the hinge, into the swing side) to the far jamb (the opening width from the hinge, along the segment). The sweep direction is the sign of the cross product of those two points about the hinge.

swing: { into: "/L1/b", hinge: {...}, leaf: {...}, jamb: {...}, ccw: false }

An opening with style:sliding or style:auto has no trace — it retracts towards the hinge side. FormOpening.sliding is set.

Columns​

The position of a column is written nowhere. It emerges where a grid intersection meets a floor.

The population of floors is: on that level, neither exterior nor void, has a region, and is not a semi-outdoor space that holds up nothing but sky. The last clause excludes roof gardens and terraces — semi-outdoor with no floor above — because a column there has nothing to hold up.

If the declaration names grids, only those are considered; otherwise all of them. The scan runs X outer, Y inner. If the intersection lies inside one of the floors' pieces (points on an edge count as inside, within POINT_EPS), a column stands there.

Two columns never stand on the same intersection — the earlier declaration wins. That is why declaration order is meaning, and why canonical JSON does not reorder columns.

A column's z range runs from that level's FL to FL + pitch.

Floors, ceilings and roofs​

The scan goes level by level in ascending z, spaces in declaration order within a level, and floor → ceiling → roof within a space. Every outline is a derived piece.

SlabConditionz range
Floornot void, not exterior, and the level has slabFL − slab … FL
Ceilingnot ceiling:0, not void / exterior / semi-outdoor / vertical circulation, and a ceiling height is determinedFL + h − CEILING_T … FL + h
Roofnot exterior, not semi-outdoor. Only over the part with no space aboveapex − thickness … apex

The absence of a floor is not the absence of a roof — a void is roofed too. A void with nothing above it is either a shaft closed by a skylight or a courtyard open to the sky, and the latter is derived as semi-outdoor. So only exterior and semi-outdoor are excluded. Conversely, voids and semi-outdoor spaces count as coverers. Coverage is taken from every level above, not only the one directly above, and subtracted using derived shape. Subtracting allocations would count a slice of an obliquely cut upper storey as "covered" and leave no roof beneath it.

The apex and thickness switch on whether there is a level above.

a level above : apex = z of that level     ; thickness = its slab ?? ROOF_T
none          : apex = FL + h + ROOF_T     ; thickness = ROOF_T

When there is a level above, the ceiling height is never read. So a roof is generated even where no ceiling height is determined. With nothing above and no ceiling height, the shape comes out thin — but SUF01 already blocks that state as an error.

Tiles whose remaining area is at or below AREA_EPS do not become roof.

In a building where a tower sits on a podium, this rule produces the podium roof without anyone writing it.

Neighbouring pages​