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The plan — classified 2D entities

A plan is not a horizontal section. Slicing a solid does not give you a plan. Four things never come out of it, however accurately you cut.

  • The swing of a door — a symbol of movement; there is no matter there
  • The look-up into a void above — what is above the cut, dropped onto the storey below
  • The break line itself — the position of the fact that something was cut
  • The descending run — what is visible below the cut

Tell consumers to "slice the solid" and each of them will invent those four. The projection of an upper void really did fall out this way: the bundled examples are full of them, and a viewer's plans showed none.

So Form holds the plan as a classified set of 2D entities.

form.plans   // one per level
// { level: "L1", cut: 1200, cutZ: 1200, entities: [ … ] }

Area-hosted components sit beside that classified set in form.components. They have physical footprints but no vertical extent, so the model does not claim whether the cut plane cuts them. Their plan SVG remains presentation and is joined to the footprint only by the drawing layer. See Area-hosted components.

Entities​

interface PlanEntity {
  class: "cut" | "below" | "above" | "swing" | "anchor";
  of: "space" | "boundary" | "opening" | "column" | "run";
  ref: string;                 // identity of the subject
  role?: "outline" | "tread" | "break" | "arrow";
  polygon?: Pt[];
  lines?: Seg2[];
  arc?: { cx, cy, r, from, to, ccw };
  anchor?: { x, y, up? };
}
ClassMeaning
cutwhat the cut plane cut
belowwhat is visible below the cut
abovethe projection of what is above the cut
swingthe trace of movement (a door)
anchora seat for a symbol

role says what kind of line a vertical-circulation entity is in drafting terms — the side lines of a run (outline), nosings or step marks (tread), the break line (break), the direction-of-travel arrow (arrow).

L1 of examples/two-rooms.muro holds 25 entities.

cut/space 2   cut/boundary 11   above/boundary 4   below/boundary 2
cut/opening 4   swing/opening 2

You can read the wall intervals splitting across three classes. Intervals spanning the cut (z = 1200) are cut; head walls are above; sill walls are below.

The cut height is an input to Form, not part of it​

derive(model)              // cut = 1200 (CUT_HEIGHT)
derive(model, { cut: 900 })

FormPlan.cut is the height above FL and cutZ the height in world coordinates. Changing the cut height changes the classification — that is a different slice of the same shape, not a different shape.

Walls and openings​

If a boundary has matter, each of the intervals it was split into by openings becomes one entity. Its z range is compared with the cut plane: spanning it gives cut, a top below it gives below, otherwise above. A boundary with no matter (type:open) carries only its centre segment.

An interval carries both the footprint and the centre line. The footprint is the body with its junctions settled, so at a corner it is not the centre line thickened and the axis cannot be recovered from it. Drawing the interval as thick or as a single line (a rail or fence that does not enclose) is a judgement about appearance; repairing a corner is not one, and there is nothing left on the drawing side to repair.

An opening carries the band of the leaf itself, and a door is followed by a swing entity. Sliding and automatic doors have no arc — only the segment from hinge to leaf tip.

The black band in a plan is the "cut interval" of Form itself. There is nowhere an operation that paints over it in the paper colour.

Ascending and descending runs​

One plan shows two runs — the one ascending from this level and the one descending to it. That is why a stair appears differently on every storey, and it is the fact that a plan is a section cut at that level.

The ascending run has, per part, a visible interval decided by comparing its z range with the cut plane. If the cut is at or above the top of the part it is wholly visible; at or below the bottom, wholly hidden; spanning, it breaks where it crosses. The test is purely geometric and never keys on the index of the part — parallel units are cut at the same height, and only this way does the second unit get a window.

The descending run appears in what its twin ascending run left uncovered. To be a twin, the four coordinates of the rectangle must match within SPAN_EPS, and direction, form, device and part count must all agree. Matching on position alone produces mirror images. With no twin, the descending run is wholly visible.

Ascending runs land in cut, descending runs in below.

Nosings are laid out from the part's t0 at the going interval, and anything outside the visible interval is dropped. Escalator step marks are laid out from the start of the visible interval at a constant STEP_MARK (400mm) pitch.

Arrows are drawn per unit for an escalator, and for a stair or ramp one per departing flight (on the ascending face) or arriving flight (on the descending face). The direction is decided by the way people travel and nothing else. An escalator points the same way on both faces; a stair or ramp reverses on the descending face — the machine's direction is fixed, a person's changes with the face. A visible interval that does not exceed ARROW_SPAN_MIN (900mm) gets no arrow — an interval of exactly 900mm gets none either (derivation constants).

That is the classified geometry, not the final stair symbol. planMarks reverses the descending-face arrow of a stair so the paper arrow always points towards increasing elevation. The original direction-of-travel entity remains unchanged for consumers that need it.

anchor returns only the seat for the annotation. The riser count and the slope live on the vertical run; turning them into words is the drawing side's job.

The break line is a single segment crossing the full width of the run at the position where it spans the cut plane. Its appearance is a consumer decision; the SVG drawing scales the 10 by 40 break glyph to the run width and rotates it 30 degrees.

The projection of an upper void​

For the two spaces joined by a void boundary, the derived shape of the upper space drops onto the lower plan as above. Dropping the allocation instead would show a void cut by a drawn line in its uncut form.

Site boundaries appear on the lowest storey​

Form.site carries the given site polygon regardless of level.

koyu plan treats the lowest storey's plan as a site plan too, and draws the site boundary there — and only there — as a dash-double-dot line (grid lines are dash-dot, so the two are told apart by style). That is a judgement about the composition of the sheet, not shape. Neither which level it lands on nor the line style is inside what freezes.

Neighbouring pages​