code: private void buildExternalLink(MeshData tile, Poly node, MeshData neighbourTile) {
  		if (neighbourTile.header.bmin[0] > tile.header.bmin[0]) {
  			node.neis[PolyUtils.findEdge(node, tile, neighbourTile.header.bmin[0], 0)] = NavMesh.DT_EXT_LINK;
  		} else if (neighbourTile.header.bmin[0] < tile.header.bmin[0]) {
  			node.neis[PolyUtils.findEdge(node, tile, tile.header.bmin[0], 0)] = NavMesh.DT_EXT_LINK | 4;
  		} else if (neighbourTile.header.bmin[2] > tile.header.bmin[2]) {
  			node.neis[PolyUtils.findEdge(node, tile, neighbourTile.header.bmin[2], 2)] = NavMesh.DT_EXT_LINK | 2;
  		} else {
  			node.neis[PolyUtils.findEdge(node, tile, tile.header.bmin[2], 2)] = NavMesh.DT_EXT_LINK | 6;
  		}
  	}
docs: In case of external link to other tiles we must find the direction