Adds 3DTILES_implicit_tiling extension #414
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@sanjeetsuhag congrats on this! Please bump to me when it is ready for me to review. 😄 CC @lilleyse |
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| Every level of the tree can be thought of as a fixed grid of equally sized tiles, where the level occupies the same space as the previous level but with double the amount of tiles along each axis that gets split (2 in case of [quadtree](https://en.wikipedia.org/wiki/Quadtree) and 3 in case of [octree](https://en.wikipedia.org/wiki/Octree)). |
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equally sized tiles - in Cartesian coordinates yes, but not necessarily in lat/long. I think people will get the point but can it be phrased differently?
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| #### External Tileset at Implicit Location | ||
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| An external tileset may exist outside the file structure of its parent tileset, with the root of the external tileset being present in the `tile.json` at the implicit location of the tile with subdivision state `10`. |
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I still think the list of external tilesets uris could go in the implicit tiling extension JSON to avoid the indirection and the need to store physical tile.json files. It would look similar to how string properties are stored in 3DTILES_tile_metadata but the array length would be the number of tiles with the 10 code. I'm not too worried about the file size; as long as it's a binary file the client is free to use HTTP range requests to get the external tileset uris it needs.
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| # 3DTILES_implicit_tiling Extension | |||
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Like CesiumGS/glTF#1, all sample tilesets that we send from here on out should have an extras.draftVersion that follows semver and distinguishes it from future revisions.
"extensions": {
"3DTILES_implicit_tiling": {
"extras": {
"draftVersion": "0.0.0"
},
...
}
}
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Just to clarify, no need to edit the examples in the spec, just make sure to include in sample tilesets we send out.
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| # 3DTILES_implicit_tiling Extension | |||
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Are there plans to add contentBoundingVolume for this draft?
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No, that'll be added to the next version, primarily because it seems like we'll be changing the way bounding volumes get divided.
| When a tile divides externally, the content and metadata for the root tile are obtained from the external tileset. | ||
| ##### External Tileset at Implicit Location | ||
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| An external tileset may exist within the file structure of its parent tileset, with the root of the external tileset being present at the implicit location of the tile with subdivision state `01`. |
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This hints at it, but it needs to be clearer that tiles in implicit external tilesets exist within the global context of the parent tileset.
Though what happens if the external tileset is a different tiling scheme or bounding volume type? It doesn't make as much sense.
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| # 3DTILES_implicit_tiling Extension | |||
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Meta question, how does implicit tiling handle the case where a building is situated between two tiles? Does it get cut in half? Can looser bounding volumes be stored in tile metadata so that it extends itself to contain the building. See the Canary Wharf example in https://github.com/CesiumGS/3d-tiles/tree/master/specification#quadtrees.
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Implicit tiling has strict bounding volume subdivision, the building would get cut in half.
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Ok, that's how I read it right now too. I think we should consider this case some more for the next draft so I'm going to mark it back to unresolved.
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| | |Type|Description|Required| | ||
| |---|----|-----------|--------| | ||
| |**boundingVolume**|`object`|A bounding volume that encloses the tileset.|☑️ Yes| |
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transform should also be included in this list
…alGraphicsInc/3d-tiles into 3DTILES_implicit_tiling
…/3d-tiles into 3DTILES_implicit_tiling
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Sandcastle for bounding volume diagrams: |
…TILES_implicit_tiling
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Superseded by #444 |
This extension enables 3D Tiles to better support implicit tiling schemes. Specification is available here.