Baidu tile numbering is offset from the XYZ grid

• The XYZ formula returns `x = 215971, y = 99264` while the network panel shows `x = 209317, y = 96843`
• Each stitched row is offset, and the error grows toward the east
• Tiles exist only from level 3 upward; levels 1 and 2 are schematic only

1. Record a real tile URL for a known place at z18 from the Baidu map
2. Compute the same point with the XYZ formula and diff the numbers
3. Divide the diff by 2^z to tell an origin shift from a scale difference
4. Check whether BD-09 lng/lat was mixed with BD09MC plane coordinates
5. Compare a resolution-based computation against the observed numbering

Do not apply XYZ math to Baidu tiles: use the Baidu JS API `getTileUrl` or a maintained Leaflet Baidu plugin. If you must compute, divide BD09MC metres by the level resolution and then add Baidu's own origin offset.

const z = 18;
const lng = 116.410172, lat = 39.916634;
const n = Math.pow(2, z);
const xXyz = Math.floor((lng + 180) / 360 * n);          // 215971
const yXyz = Math.floor((1 - Math.log(Math.tan(lat * Math.PI / 180) +
             1 / Math.cos(lat * Math.PI / 180)) / Math.PI) / 2 * n);  // 99264
const xBaidu = 209317, yBaidu = 96843;

const RES = [0, 0, 0,
  262144, 131072, 65536, 32768, 16384, 8192, 4096,
  2048, 1024, 512, 256, 128, 64, 32, 16, 8];

function baiduTile(mx, my, z) {
  const res = RES[z];
  const x = Math.floor(mx / res);
  const y = Math.floor(my / res);
  return [x, y];
}
baiduTile(12962180, 4859510, 18);
// 与百度实际编号 209317 / 96843 仍差一个平移量，不能直接用

• Dividing BD09MC coordinates by the resolution and assuming the quotient is final, while the platform origin offset remains
• Converting BD-09 lng/lat with the XYZ formula, which mixes geographic and projected units