Candidate source formats — roadmap (not yet supported)

A crawl of the GIS / CAD-AEC / VFX / cultural-heritage communities for tiled / streamable formats we don't yet ingest. Ranked by value × feasibility for a live → 3D Tiles adapter. (Already supported: COPC, Potree 1.x/2.0, EPT, I3S/SLPK, streamed-SOG, LCC, RAD, 3D Tiles packages, Bentley 3MX, Bing Maps 3D.)

Tier 1 — open enough + cleanly tiled + remotely consumable:

Tier 2 — feasible, caveated:

• Cesium quantized-mesh .terrain + Terrarium / Mapbox Terrain-RGB raster-DEM tiles → TIN via martini/delatin (JS) — the whole 2.5D terrain track (see below).
• OpenUSD / USDZ — strong VFX/heritage source (not spatially tiled); TinyUSDZ gives a Node/WASM reader. Walk the stage → emit tileset; not a streaming passthrough. (Nanite = no open format → dead end.)
• Skyline o3DML v2 — only the new variant (3D Tiles internals in a SQLite container); skip classic 3DML/MPT.

Tier 3 — integrate, don't build: Bentley iModel/iTwin (use the Mesh Export API → already 3D Tiles) · Cesium ion & Google Photorealistic 3D Tiles (already 3D Tiles — consume/target; Google ToS forbids re-serving/caching).

Tier 4 — blocked / low ROI: Autodesk ReCap .rcp/.rcs — confirmed no open reader OR writer (PDAL/CloudCompare/PCL/Open3D none; FME writer-only); can't ingest remote .rcp; and Autodesk can't consume 3D Tiles natively (Cesium is Bentley's now → native import is in MicroStation/iTwin; Autodesk only has a Revit→3D Tiles exporter). Realistic bridge is a future → E57/LAS export (formats ReCap ingests), not an .rcp writer. · Bentley 3SM (closed, no spec). · Splatter (splatter.app) — hosted Gaussian-splat viewer, not a file format: content is addressed by an opaque ID against a private backend, so there's nothing a converter could parse. Tracked as a rendering-technique reference, not a source format — see splatter-app.md for the full status writeup and observed API surface.

Implemented adapters (plans: streaming-adapter-plans.md):

• ✅ Bentley 3MX — GET /stream/tileset.json?format=threemx&url=<Scene.3mx | root.3mxb>. Parses 3MXBO node trees, serves lazy external-tileset fragments per .3mxb, decodes OpenCTM (MG1/LZMA) geometry via vendored js-openctm → glTF + JPEG baseColor. Verified live against the colorwlof/Unity-3mxb fixture (textured GLB tiles render; decoded bbox matches node bbMin/bbMax). Georef via SRS+SRSOrigin when present.
• ✅ Bing Maps 3D — GET /bing/tileset.json?root=<quadkey>&g=<genid>&maxLevel=<L>[&decompress=1]. tf=3dv4 GLB (Draco + KTX2, ECEF in node matrix) served as-is; quadtree of quadkeys as lazy fragments, availability by HTTP probe, geographic region bounding volumes. Verified live (Berlin, keyless g=15340). The lazy fragments are their own route, GET /bing/fragment/<face>-<level>-<x>-<y>.json?g=<genid> — a partial explicit tileset continuing the tree from that boundary node; tileset.json's deep tiles reference these by absolute URL, fetched only as the camera refines in. Example: /bing/fragment/0-3-3-2.json?g=15530.
• Nexus .nxs/.nxz — moderate, postponed: header parse + Corto decode exist in JS but are WebGL/Worker-coupled (port needed), Corto not on npm, DAG→tree mapping is the thorny bit.

2.5D terrain (separate track, future)

Deliberately out of scope so far, but worth showing: DEM raster tiles → TIN → 3D Tiles/quantized-mesh.

• Cesium quantized-mesh (spec) — TIN, quadtree-in-TMS + layer.json; an output target as well as input.
• Terrarium ((R*256+G+B/256)-32768, token-free on AWS) and Mapbox Terrain-RGB/DEM (token-gated) — raster-DEM XYZ tiles.
• Bridge libs (Node-native): martini (RTIN), delatin (Delaunay), pydelatin/pymartini (incl. decode_ele for Terrarium/Terrain-RGB) → feed quantized-mesh-encoder or a glTF terrain tileset.

Verify-before-relying caveats from the crawl: itowns' current 3MX support is unconfirmed against master; Google 3D Tiles byte-range behavior is observed, not published; OSGB GE/bounding-volume metadata must be synthesized (the format only implies it via PagedLOD ranges).