Cesium 3D Tiles core concepts

This chapter explains the coordinate and streaming ideas that every Cesium scene depends on. Field-level component details live in later chapters.

Coordinate systems

CesiumGeoreferenceComponent owns the root map from LLH/ECEF into the level. Default placement is CartographicOrigin: the chosen lon/lat/height becomes engine (0,0,0), with +X East, +Y North, +Z Up. TrueOrigin puts ECEF zero at the engine origin (rarely useful for Earth-scale work).

Scale 1.0 means one Earth meter equals one engine meter. Lower the scale to shrink the planet for demos that must fit a small playable volume.

Query transforms at runtime via CesiumGeoreferenceRequestBus (LongitudeLatitudeHeightTo*, *ToLongitudeLatitudeHeight, SetOriginLongitudeLatitudeHeight). See Georeference and tilesets.

Screen-space error (SSE) and LOD

Tilesets refine when a tile’s projected geometric error exceeds the maximum screen-space error budget (pixels). Defaults:

Lower SSE → sharper / heavier. Raise SSE for low-end or distant overview flights.

Additional LOD knobs (full tables in Georeference and tilesets):

• DPI scaling — optionally stretch pixel budgets by OS DPI so high-DPI displays keep perceived detail.
• Frustum / fog culling — skip off-screen or fog-hidden tiles; disable carefully when using LOD cross-fades.
• Occlusion culling — experimental GPU depth queries; off by default.
• Adaptive SSE — under load the controller can temporarily coarsen then fall back toward ×1.0 when idle.

Multiple cameras contribute frustums: editor viewports, game cameras, render-to-texture, XR eyes, plus per-tileset additional camera entities. Per-tileset source toggles filter which of those feed LOD selection — see Anchors and navigation.

Origin shift and LargeWorld

At global scale, storing world positions as single-precision floats near ECEF magnitudes destroys local precision. Dawn’s double-precision rendering keeps authoritative positions in double precision and recenters a float render origin near the viewer.

CesiumOriginShiftComponent (usually on the camera) drives that recenter:

Distance threshold and cell size ≤ 0 inherit LargeWorld settings. Without LargeWorld + Origin Shift, distant content jitters and tiles may fail to refine correctly.

Camera moves across the globe
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Origin Shift (threshold / cell)
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LargeWorld RenderOriginService
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GPU sees float positions relative to nearby origin

Data path in one picture

Source (ion / URL / file)
 → cesium-native selection (SSE, culling, cameras)
 → glTF decode + Atom upload (+ optional PhysX)
 → georeference + origin shift
 → overlays draped into material slots
 → credits / metadata / script buses

What Cesium owns vs what it does not

Optional Bridge components can notify Terrain, World Streaming, or NavMesh rebuilds when tiles stream — they do not replace those Gems. Default bridge mode is Coexist (diagnostics only). See Environment, metadata, and bridges.

Next steps

• Georeference and tilesets — configure origins and tilesets.
• Anchors and navigation — place entities and fly the globe.
• Configuration and debugging — registry defaults and diagnostics.