Sketch exchange macro and import

A coordinate or length as the text the macro passes, in meters.

m = round₁₂(round₉(v) × mm per unit ÷ 1000)

The value is fixed to 9 decimals of a drawing unit, multiplied by millimeters per unit and divided by 1000, fixed again to 12 decimals of a meter, and then written by num. The comment gives the reason for the first rounding: solver noise below 1e-9 is dropped.

const M = (v) => num(Number((Number(v.toFixed(9)) * k / 1000).toFixed(12)));   // drawing units → metres (the API's unit); solver noise below 1e-9 dropped
const ents = [...doc.model.values()];

A number as text in the macro.

v.toPrecision(15)

15 significant digits; 17 are needed to give back every 64-bit number exactly. Very large or small values are written in exponent form with 15 digits.

const num = (v) => { const s = Number(v.toPrecision(15)).toString(); return /e/i.test(s) ? v.toExponential(14).replace('e', 'E') : s; };

The size of the drawing's unit in millimeters.

inch 25.4; foot 304.8; yard 914.4; mil 0.0254; microinch 0.0000254

The values are the defined sizes. A unit that is not in the table is treated as millimeters and a note says so.

const UNIT_MM = { '': 1, millimeters: 1, centimeters: 10, meters: 1000, inches: 25.4, feet: 304.8, yards: 914.4, mils: 0.0254, microinches: 0.0000254 };

The start and end points of an arc, which the macro needs beside its center.

start = c + r(cos a₀, sin a₀); end = c + r(cos a₁, sin a₁)

The ends are computed from the stored center, radius and angles in 64-bit, then each coordinate is rounded by M. The center and the two ends are rounded separately, so the written ends can sit off the written circle by the rounding step.

case 'arc': {
  const s = [e.cx + e.r * Math.cos(e.a0), e.cy + e.r * Math.sin(e.a0)], t = [e.cx + e.r * Math.cos(e.a1), e.cy + e.r * Math.sin(e.a1)];
  const i = seg('swSkMgr.CreateArc(' + [M(e.cx), M(e.cy), 0, M(s[0]), M(s[1]), 0, M(t[0]), M(t[1]), 0, 1].join(', ') + ')', 'arc ' + e.id);

The center of the arc between two polyline vertices with a bulge.

θ = 4·atan(b); r = |chord ÷ (2·sin(θ ÷ 2))|; center = middle ± r·cos(θ ÷ 2) across the chord

The chord direction is divided by the chord length without a check, so two equal vertices with a bulge give a non-finite center. For a nearly flat bulge sin(θ ÷ 2) is small and the radius is large.

function bulgeCentre(p, q, b) {
  const th = 4 * Math.atan(b), c = Math.hypot(q.x - p.x, q.y - p.y), r = Math.abs(c / (2 * Math.sin(th / 2)));
  const h = r * Math.cos(th / 2) * (b > 0 ? 1 : -1), ux = (q.x - p.x) / c, uy = (q.y - p.y) / c;
  return { x: (p.x + q.x) / 2 - uy * h, y: (p.y + q.y) / 2 + ux * h };
}

The value given to each dimension in the macro.

angle: degrees × π ÷ 180; length: M(value)

Angles are multiplied by π and divided by 180 in that order and written with 15 significant digits. Lengths go through the same 9- and 12-decimal rounding as coordinates.

const value = c.type === 'angle' ? num(c.value * Math.PI / 180) : M(c.value);
dims.push('swModel.ClearSelection2 True');

Builds an arc from the center, start and end points of an imported sketch.

r = |start − center|; a₀ = atan2(start − center); a₁ = atan2(end − center), each in [0, 2π)

The radius is the start point's distance from the center; the end point gives only an angle, so an end that is not at that distance is moved onto the circle.

const c = P.get(s.c), st = P.get(s.s), en = P.get(s.e);
ents.push({ type: 'arc', layer: s.construction ? 'CONSTRUCTION' : '0', cx: c.x, cy: c.y, r: Math.hypot(st.x - c.x, st.y - c.y), a0: ang(st.y - c.y, st.x - c.x), a1: ang(en.y - c.y, en.x - c.x) });

The value each imported dimension gets, and the parameter that drives it.

parameter = round(value × 1e9) ÷ 1e9

The constraint first takes the file's value, in millimeters or degrees. The parameter that then drives it is written as text from the value rounded to 9 decimals.

if (Number.isFinite(p.value) && p.value > 0) c.value = p.value;   // millimetres; angles in degrees
params.vars.push({ name: c.name, expr: formatNumber(Math.round(c.value * 1e9) / 1e9) });