LCC — Lixel CyberColor (XGRIDS) data organization

Sources: https://github.com/xgrids/LCCWhitepaper · https://developer.xgrids.com/#/document?titleId=en-1720509291851 License: XGRIDS White Paper License (attribution required: "Data Organization Format originated from XGRIDS"; derivatives must be published under terms no less open; no AI-model training that competes with XGRIDS). Quote/cite, don't relicense.

LCC is XGRIDS's chunked, LOD-native container for 3D Gaussian Splatting from Multi-SLAM capture (L1/L2/K1/PortCam/Drone). Smaller than PLY, progressive streaming, integrations for Three.js, Unity, Unreal, Cesium. Target for a future lcc-to-3dtiles converter.

File set

Terms: Node = a chunk at one LOD level · Index = uint32 packing x(low16)/y(high16) of a partition cell · Unit = group of Nodes sharing one Index · Level = one LOD level. fileType: Portable = RGB only (no Shcoef.bin) · Quality = RGB + 3rd-order SH.

meta.lcc (key fields)

version, source (lcc/ply/splat/none), dataType (L1/L2/K1/…), totalSplats, totalLevel, cellLengthX/Y (Node size, m), indexDataSize (bytes/Unit index), offset/shift/scale/epsg (global), splats[] (per-LOD counts, LOD0→), boundingBox (min/max, no env), encoding (COMPRESS), fileType, attributes[] (per-property min/max for dequant: position, normal, color, shcoef, opacity, scale, + env* variants). Observed sample Guan_Temple: version 3.0, 11.4M splats, 4 levels, indexDataSize 68 (= index uint32 4 + 4 levels × {PointsCount u32, Offset u64, Size u32 = 16} = 68).

Index.bin (per Unit, little-endian, indexDataSize bytes)

index u32 · then per LOD level: PointsCount u32, LODOffset u64 (into Data.bin), LODSize u32. Total Units = fileSize / indexDataSize. Unit AABB starts at boundingBox.min, cell size (cellLengthX,cellLengthY).

Data.bin per-splat (32 B basic; +64 B SH when Quality — SH offset/size = 2× the Data offset/size)

• position xyz: 3× float32, used directly.
• scale xyz: 6 bytes → extract xyz as Int (per axis), lerp via attributes.scale min/max.
• rotation uint32: 10/10/10/2 packed "smallest-three". Decode (HLSL from spec): pq = ((enc&1023)/1023, (enc>>10&1023)/1023, (enc>>20&1023)/1023, (enc>>30&3)/3); idx=round(pq.w*3); q.xyz = pq.xyz*√2 − 1/√2; q.w = sqrt(1−dot(q.xyz)); reorder by QLut[idx] ({3,0,1,2, 0,3,1,2, 0,1,3,2, 0,1,2,3}).
• color uint32 RGBA → /255 → [0,1].
• opacity: lerp via attributes.opacity min/max.

Shcoef.bin (Quality only, 64 B/splat = 15 coeffs)

Packed-11 per coeff: DecodePacked11(enc) = ((enc&2047)/2047, (enc>>11&1023)/1023, (enc>>21&2047)/2047), then lerp via attributes.shcoef min/max. 15 coeffs (sh1..sh15) → SH degree 3.

Environment.bin — same decode as above but using the env* attribute min/max ranges.

Collision.lci — header (headerLen) + mesh data (verts + tri indices) + BVH (preorder,

32 B/node; internal: bbox f32×6, right u32@24, splitAxis u16@28, flag u16@30; leaf: bbox, faceOffset u32@24, faceCount u16@28, flag 0xFFFF@30). Optional for rendering — skippable.

Mapping to 3D Tiles (planned lcc-to-3dtiles)

Units×Levels form a quadtree-ish LOD grid → 3D Tiles HLOD: each Unit's per-LOD Node = a tile, coarsest level as ancestor (REPLACE) down to LOD0, decoded splats re-encoded to SPZ-v2 GLB (reuse spzGlb.js). Position direct; rotation via the 10-10-10-2 decode above (→ xyzw); scale lerp+exp?; color/255; opacity lerp; SH (Quality) → KHR SH_DEGREE_* attributes. Coordinate frame per Fig.2 (right-handed) → emit boxes Z-up (RX+90°) like the RAD/SOG paths. Environment as an always-coarse ADD child. NB: this LCC sample is version 3.0 (whitepaper documents 5.0) — field layouts match but confirm against the actual bytes before trusting any single field.