Tile Header Hierarchy - An initial, "minimal" set of data listing the hierarchy of available tiles, with minimal information to allow an application to determine which tiles need to be loaded based on a certain viewing position in 3d space.
Tile Header - A minimal header describing a tiles bounding volume and a screen space error tolerance (allowing the tile to be culled if it is distant), as well as the URL to load the tile's actual content from.
Tile Cache - Since the number of tiles in big tilesets often exceed what can be loaded into available memory, it is important to have a system that releases no-longer visible tiles from memory.
Tileset Traversal - Dynamically loading and rendering 3D tiles based on current viewing position, possibly triggering loads of new tiles and unloading of older, no-longer visible tiles.

Data Format

Check Tiles3DLoader, CesiumIonLoader | | and I3SLoader.

Helper Classes

Tileset Traversal Support

To start loading tiles once a top-level tileset file is loaded, the application can instantiate the Tileset3D class and start calling tileset3D.update(viewport).

Since 3D tiled data sets tend to be very big, the key idea is to only load the tiles actually needed to show a view from the current camera position.

The Tileset3D allows callbacks (onTileLoad, onTileUnload) to be registered that notify the app when the set of tiles available for rendering has changed. This is important because tile loads complete asynchronously, after the tileset3D.update(...) call has returned.

Additional Information

Coordinate Systems

To help applications process the position data in the tiles, 3D Tiles category loaders are expected to provide matrices are provided to enable tiles to be used in both fixed frame or cartographic (long/lat-relative, east-north-up / ENU) coordinate systems:

cartesian WGS84 fixed frame coordinates
cartographic tile geometry positions to ENU meter offsets from cartographicOrigin.

Position units in both cases are in meters.

For cartographic coordinates, tiles come with a prechosen cartographic origin and precalculated model matrix. This cartographic origin is "arbitrary" (chosen based on the tiles bounding volume center). A different origin can be chosen and a transform can be calculated, e.g. using the math.gl Ellipsoid class.