Polygon crossing the antimeridian renders as a band across the whole globe

• The polygon becomes a thin band spanning the full map width and cutting through Africa.
• turf.area returns about 4.9e14 square metres against a real area of roughly 1.1e12, two orders of magnitude off.
• The feature bbox is close to 360 degrees wide.

1. Scan consecutive vertices of the ring and log any pair whose longitude difference exceeds 180; the page shows [179.5, -16.8] followed by [-179.5, -16.9], a jump of 359.
2. Check the feature bbox width; a value near 360 degrees confirms an antimeridian crossing.
3. Compare turf.area with the known area; a result two orders of magnitude too large confirms it.
4. Check whether the source came from a Shapefile, which also cannot represent crossing rings.
5. Split the ring at the antimeridian, then re-measure and compare.

Unwrap the ring by shifting each vertex by plus or minus 360 until the step from the previous vertex stays within 180, then emit two polygons: one translated +360 for the western half and one translated -360 for the eastern half. The sum of turf.area over both halves should come back near 1.1e12 square metres.

const ring = f.geometry.coordinates[0];
for (let i = 1; i < ring.length; i++) {
  const d = Math.abs(ring[i][0] - ring[i - 1][0]);
  if (d > 180) console.log('跨线点对', ring[i - 1], ring[i], d);
}
// [179.5, -16.8] [ -179.5, -16.9]  d = 359

function unwrapRing(ring) {
  let prev = ring[0][0];
  return ring.map(([x, y], i) => {
    let nx = x;
    if (i > 0) {
      while (nx - prev > 180) nx -= 360;
      while (nx - prev < -180) nx += 360;
    }
    prev = nx;
    return [nx, y];
  });
}
const u = unwrapRing(ring);
const left = u.map(([x, y]) => [x < 0 ? x + 360 : x, y]);
const right = u.map(([x, y]) => [x > 180 ? x - 360 : x, y]);

const polys = [left, right].map(r => ({
  type: 'Feature',
  properties: f.properties,
  geometry: { type: 'Polygon', coordinates: [r] }
}));

• Shifting every negative longitude by +360, which keeps the ring continuous but moves it outside the basemap tile range.
• Trying to solve it with a renderer option: Leaflet and Mapbox GL both treat geometry as planar, so the split has to happen in the data.