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Geometry helpers

Five functions over polygons and rectangles. Coordinates are millimetres; areas come back in m².

import { envelopeGaps, pointInPolygon, polyBounds, polygonAreaM2, rectToPoly } from "@kensnzk/koyu";

Not one judgement lives here. Neither "does the building run off the site?" nor "is there a hole in the envelope?" is answered here — those are site.escape and envelope.gap in validate. What is here is only the numbers and shapes those judgements read.

polygonAreaM2​

function polygonAreaM2(points: Pt[]): number

The shoelace area of a polygon, in m². Winding does not matter — it is the absolute value of the signed area, so clockwise and counter-clockwise give the same number.

pointInPolygon​

function pointInPolygon(p: Pt, poly: Pt[], eps?: number): boolean

Whether a point is inside a polygon. On the boundary counts as inside. eps is how wide a band counts as "on an edge"; the default is 1 mm.

polyBounds​

function polyBounds(poly: Pt[]): Rect

The bounding rectangle of a vertex list.

rectToPoly​

function rectToPoly(r: Rect): Pt[]

A rectangle as a vertex list, counter-clockwise, in the order (x1,y1) → (x2,y1) → (x2,y2) → (x1,y2).

That winding is a promise. The derivation that reads a compass direction from an edge's direction — an edge running +x faces south, +y east, −x north, −y west — depends on it.

import { pointInPolygon, polyBounds, polygonAreaM2, rectToPoly } from "@kensnzk/koyu";

const poly = [{ x: 0, y: 0 }, { x: 10000, y: 0 }, { x: 10000, y: 10000 }, { x: 0, y: 10000 }];
console.log(polygonAreaM2(poly), pointInPolygon({ x: 5000, y: 5000 }, poly),
  pointInPolygon({ x: 12000, y: 0 }, poly), pointInPolygon({ x: 0, y: 5000 }, poly), polyBounds(poly));
console.log(polygonAreaM2([...poly].reverse()));
console.log(rectToPoly({ x1: 0, y1: 0, x2: 3600, y2: 4000 }));
100 true false true { x1: 0, x2: 10000, y1: 0, y2: 10000 }
100
[
  { x: 0, y: 0 },
  { x: 3600, y: 0 },
  { x: 3600, y: 4000 },
  { x: 0, y: 4000 }
]

The third pointInPolygon sits exactly on an edge and comes back true. Reversing the winding leaves the area unchanged.

envelopeGaps​

function envelopeGaps(model: Model, s: Space): Segment[]

Returns the stretches of a space's perimeter that face nothing at all — edges opposite neither another space nor a declared boundary to the exterior. Holes in the envelope.

Default boundaries are never derived against a space with no region, so forgetting a boundary to the exterior is silently the absence of a wall. This derivation exists to put that into words.

Stretches shorter than SPAN_EPS (1 mm) are dropped. A space with no region, or with no settled level, gives an empty array.

import { envelopeGaps, parse } from "@kensnzk/koyu";

const g = parse(`grid X 0 3600 7200
grid Y 0 4000
level L1 0 h:2400 slab:150
space /L1/a room X1..X2 Y1..Y2
space /L1/b room X2..X3 Y1..Y2
space /out exterior
boundary /L1/a /out edge:W`);

for (const s of ["/L1/a", "/L1/b"]) {
  console.log(s, envelopeGaps(g, g.spaces.get(s)!).map((x) => `${x.edgeOfA} ${x.x1},${x.y1}→${x.x2},${x.y2}`));
}
/L1/a [ 'S 0,0→3600,0', 'N 0,4000→3600,4000' ]
/L1/b [ 'S 3600,0→7200,0', 'E 7200,0→7200,4000', 'N 3600,4000→7200,4000' ]

The W side of /L1/a is covered by boundary /L1/a /out edge:W, and its E side faces /L1/b, so what remains — S and N — comes back as holes.

What you get is a Segment: endpoints, whether it is horizontal, and which side of the a-space it belongs to. It carries no length, so measure from the endpoints if you need one.

Geometric tolerances​

The numbers that decide how different two things must be to be different things live in one place: see TOLERANCES. Both the default width for "on an edge" (POINT_EPS = 1 mm) and the minimum length of an envelope gap (SPAN_EPS = 1 mm) are there.

See also​