Assistant answers: what is above an element

How the precision is kept

The boxes are taken from the 3D viewer's batches, whose positions are a Float32Array (ifc-model.js finishBatch), so every box coordinate and the gap computed from it come from 32-bit values. The comparison uses a fixed 0.02 m tolerance and the gap is rounded to 0.01 m. The answer itself says it is a survey from bounding boxes.

Open item. Take the boxes from the IFC engine's 64-bit mesh positions instead of the viewer's 32-bit batches.

1 calculation 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.

const reach = a.within_m ?? 3, tol = 0.02, top = tb.max[1];
const hit = [];
for (const [k, b] of app.bounds(ix.keys.filter((x) => x !== key))) {
  if (b.min[1] < top - tol || b.min[1] > top + reach) continue;
  if (b.max[0] < tb.min[0] || b.min[0] > tb.max[0] || b.max[2] < tb.min[2] || b.min[2] > tb.max[2]) continue;
  if (a.class && String(ix.value('cls', k - ix.keyBase)).toLowerCase() !== a.class.toLowerCase()) continue;
  hit.push({ key: k, gap: Math.max(0, b.min[1] - top) });
}
hit.sort((x, y) => x.gap - y.gap);
const pg = page(hit, a), shown = show(a, hit.map((h) => h.key));
const byClass = {};
for (const h of hit) { const cl = String(ix.value('cls', h.key - ix.keyBase) ?? '?'); byClass[cl] = (byClass[cl] || 0) + 1; }
return {
  model: app.name(), of: describe(ix, key), lookedAbove_m: reach, how: 'elements whose 3D bounding box starts within ' + reach + ' m above the top of the element and overlaps its footprint',
  total: hit.length, returned: pg.returned, next: pg.next, selected: shown, byClass, notes: ['A survey from bounding boxes: an element may be in the box without touching the footprint. Use a clash check for a decision.'],
  elements: pg.rows.map((h) => ({ ...describe(ix, h.key), gap_m: r2(h.gap) })),

In detail

Method

Axis-aligned bounding boxes in viewer space (meters, Y up): an element is listed when its lowest point is between top − 0.02 m and top + reach and its box overlaps the footprint box in X and Z.

Number types

Box corners are minima and maxima of Float32Array positions, moved by the model's placement matrix in 64-bit; the gap is a 64-bit difference of those.

Tolerances

0.02 m below the top (absolute); the reach above it is 3 m unless given.

Limits

A bounding box can overlap the footprint where the element itself does not; the tool's own note says to use a clash check for a decision.

Approach: 32-bit step, flagged

One step stores or exchanges 32-bit values that reach a number a person reads. It is listed here with its open item, and the step is either moved to 64-bit or the app will warn where the number is read.

Every policy that takes this approach