Subtree
One decoded .subtree file. Carries the availability bitstreams the layer's traversal code consults when expanding implicit children.
Spec subtree file layout (header is 24 bytes little-endian):
bytes 0..3: magic
"subt"bytes 4..7: version (uint32, currently 1)
bytes 8..15: JSON chunk byte length (uint64)
bytes 16..23: binary chunk byte length (uint64)
bytes 24..: JSON chunk
bytes 24+jsonLen..: binary chunk
The JSON describes which bytes of the binary chunk hold which availability bitstream; see SubtreeReader.parse for the actual bit-extraction logic.
Properties
Bit i = 1 iff the i-th leaf of this subtree has a child subtree at the next level boundary. Used to know which {level}/{x}/{y}.subtree URIs to fetch recursively. Empty when no children exist.
Per-content-slot availability. Most implicit tilesets have a single content slot; some publish multiple (mesh + point cloud, etc.) where each slot has its own bit pattern. Empty list = no content available in this subtree.
Bit i = 1 iff the i-th tile in level-order traversal of this subtree exists. Always non-null; constant 1 when the subtree's metadata says all tiles exist.