Resources Numerical accuracy Calculation policy
Writes a drawing sheet's lines, circles, fills and text into a DWG model or a DXF R12 file at 1 unit = 1 mm on paper.
Sheet coordinates are 64-bit paper millimeters. Every coordinate, radius and text height is rounded to six decimals (0.000001 mm) before it is written, in both formats. A filled circle becomes a 48-sided polygon under a true circle. Text height is the font size times 0.718, a two-figure approximation of the font's capital height.
6 calculations in 1 source file. The code is read from the released app when this page loads. It is the calculation people run, not a copy kept for this page.
Tests bin/test-detailcraft.mjs
The rounding applied to every number written to the file.
round(v × 10⁶) ÷ 10⁶
Math.round on the value times one million, then a division. The result is the nearest 64-bit number to a six-decimal value.
const r6 = (v) => Math.round(v * 1e6) / 1e6;Where a line of text sits and how tall it is in the DWG model.
height = size × 0.718
Position and height are rounded to six decimals. 0.718 is written in the file as the capital height of Helvetica or Arial per unit of size. The rotation is passed on as stored.
const at = { x: r6(it.x), y: r6(it.y), z: 0 };
ents.push({ ...base('DC-TEXT'), type: 'TEXT', insert: at, align: ha ? at : undefined, hAlign: ha, vAlign: 0, height: r6(it.h * CAP), rotation: it.rot || 0, widthFactor: 1, oblique: 0, style: 'DetailCraft', value: String(it.s) });The points of each line, polyline and solid fill in the DWG model.
Each coordinate is rounded to six decimals before it is stored. Polyline bulges are all zero: curves arrive already as straight pieces.
const pts = it.pts.map(([x, y]) => ({ x: r6(x), y: r6(y) }));The polygon used as the boundary of a filled circle.
(c_x + r·cos(2π·i ÷ 48), c_y + r·sin(2π·i ÷ 48))
A 48-sided polygon inside the circle, with each vertex rounded to six decimals. The circle itself is also written as a true circle with its exact center and radius.
function circlePts(it, n = 48) {
const out = [];
for (let i = 0; i < n; i++) { const a = 2 * Math.PI * i / n; out.push({ x: r6(it.c[0] + it.r * Math.cos(a)), y: r6(it.c[1] + it.r * Math.sin(a)) }); }
return out;
}How each coordinate is printed in the DXF file.
The value is rounded to six decimals and printed by String, so trailing zeros are dropped; a whole number is printed with one decimal place.
const fnum = (v) => { const n = r6(v); return Number.isInteger(n) ? n.toFixed(1) : String(n); };The line weight written for a layer, in hundredths of a millimeter.
round(w × 100)
The pen width in millimeters is rounded to a whole number of hundredths, which is how the format stores line weights.
/** The pen of an item → { name, w, dash, lt } (lineweight in 1/100 mm). */
export function penOf(it) {
const w = it.w ?? 0.25, dash = it.dash && it.dash.length ? it.dash : null;
if (!dash) { const k = KNOWN.find((p) => !p.dash && w >= p.min); return { name: k.name, w: Math.round(w * 100), dash: null, lt: 'CONTINUOUS' }; }
const k = KNOWN.find((p) => sameDash(p.dash, dash));
if (k) return { name: k.name, w: Math.round(w * 100), dash, lt: k.lt };
const key = 'DC_DASH_' + dash.map((v) => String(r6(v)).replace('.', 'p')).join('_');
return { name: key.replace(/_/g, '-'), w: Math.round(w * 100), dash, lt: key };
}The arithmetic is 64-bit, but the method or the data sets the accuracy: a solver tolerance, a mesh, a step size, a datum shift, a table. The limit is stated where the result is shown.