Two coplanar surfaces flicker and get worse with distance

• The road overlay over the ground model flickers as noise-like stripes, worst when the camera is pulled back to 5 km.
• Hiding either of the two meshes removes the flicker instantly.
• Box3 bounds show a 0.4 mm gap: upper min.y 0.0004 against lower max.y 0.0000.

1. Hide the upper mesh to confirm coplanarity rather than normals or lighting.
2. Print both meshes' world bounding boxes and compute the minimum separation.
3. Check the camera near/far ratio; anything beyond 1:100000 is visibly unstable.
4. Pull the camera from 5 m to 5 km to confirm stripe width tracks distance.

Add polygonOffset: true with polygonOffsetFactor -1 and polygonOffsetUnits -1 to the upper MeshStandardMaterial, or lift it 1-2 cm (road.position.y = ground.position.y + 0.02); for very deep scenes enable logarithmicDepthBuffer with near 0.1 and far 20000.

var b1 = new THREE.Box3().setFromObject(ground);
var b2 = new THREE.Box3().setFromObject(road);
console.log('上层最小 y', b2.min.y, '下层最大 y', b1.max.y);
// 上层最小 y 0.0004  下层最大 y 0.0000  间距 0.4 毫米

var roadMat = new THREE.MeshStandardMaterial({
  map: roadTexture,
  polygonOffset: true,
  polygonOffsetFactor: -1,
  polygonOffsetUnits: -1
});

• Raising camera far to 1e7 to stop clipping compresses depth precision further and makes the stripes coarser.
• Lowering far to a few hundred metres to sharpen depth clips the city model, which is not a fix.