# Field by field, how do the ratified KHR_gaussian_splatting extension and OpenUSD's ParticleField3DGaussianSplat schema define a splat's position, rotation, scale, opacity, spherical harmonics, kernel, projection, sorting, colour space and frame, and where do they differ?

- id: art_01M5NE1Z7PR7G9XVNEBYR7Q8G0
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T15, T19 · tags: none
- updated: 2026-10-23T22:28:12.143Z
- url: https://veyrul.com/articles/art_01M5NE1Z7PR7G9XVNEBYR7Q8G0

Both definitions store linear scale and linear 0..1 opacity (CA-B035), but defaults and fields differ: glTF KHR_gaussian_splatting requires a colorSpace string and defaults sortingMethod to cameraDistance, while the OpenUSD usdVol schema defaults sortingModeHint to zDepth and has no colour-space attribute, so a converter that copies defaults changes the declared sort metric and loses colour-space provenance. The glTF README carries an SPDX CC-BY-4.0 header and also a Khronos copyright statement limiting reproduction to the unmodified specification.

Both definitions store linear scale and linear 0..1 opacity (CA-B035), but defaults and fields differ: glTF KHR_gaussian_splatting requires a colorSpace string and defaults sortingMethod to cameraDistance, while the OpenUSD usdVol schema defaults sortingModeHint to zDepth and has no colour-space attribute, so a converter that copies defaults changes the declared sort metric and loses colour-space provenance. The glTF README carries an SPDX CC-BY-4.0 header and also a Khronos copyright statement limiting reproduction to the unmodified specification.

Curator qualifications: Licence-scope conflict preserved: CC-BY-4.0 SPDX header vs Khronos copyright statement (unmodified reproduction, IP policy); which applies to which use is not stated. Accessor component types, SH layouts and coordinate-frame statements (F1, F2, F4, F6, F7) not re-read line by line in this batch. Static reading of the same pinned bytes used in CA-B035; nothing converted.

Limitations: Static reading of the same pinned bytes used in CA-B035; nothing converted.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://github.com/KhronosGroup/glTF/blob/7cee0fcddd5730e90d488bfb5aa2e52171483dde/extensions/2.0/Khronos/KHR_gaussian_splatting/README.md",
      "note": "KHR_gaussian_splatting README at 7cee0fcd, lines 2-3, 52-54, 64-92, 549-560; usdVol schema.usda at 5b3c21a1, lines 614-626"
    },
    {
      "url": "https://github.com/KhronosGroup/glTF/blob/7cee0fcddd5730e90d488bfb5aa2e52171483dde/extensions/2.0/Khronos/KHR_gaussian_splatting/schema/mesh.primitive.KHR_gaussian_splatting.schema.json",
      "note": "KHR_gaussian_splatting README at 7cee0fcd, lines 2-3, 52-54, 64-92, 549-560; usdVol schema.usda at 5b3c21a1, lines 614-626"
    },
    {
      "url": "https://github.com/PixarAnimationStudios/OpenUSD/blob/5b3c21a1f20a77383fd6e7814ce6bde4e6c1895d/pxr/usd/usdVol/schema.usda",
      "note": "KHR_gaussian_splatting README at 7cee0fcd, lines 2-3, 52-54, 64-92, 549-560; usdVol schema.usda at 5b3c21a1, lines 614-626"
    },
    {
      "url": "https://github.com/PixarAnimationStudios/OpenUSD/blob/5b3c21a1f20a77383fd6e7814ce6bde4e6c1895d/docs/user_guides/schemas/usdVol/ParticleField3DGaussianSplat.md",
      "note": "KHR_gaussian_splatting README at 7cee0fcd, lines 2-3, 52-54, 64-92, 549-560; usdVol schema.usda at 5b3c21a1, lines 614-626"
    },
    {
      "url": "https://github.com/PixarAnimationStudios/OpenUSD/blob/5b3c21a1f20a77383fd6e7814ce6bde4e6c1895d/extras/imaging/examples/hdParticleField/py3dgsPlyToUsd.py",
      "note": "KHR_gaussian_splatting README at 7cee0fcd, lines 2-3, 52-54, 64-92, 549-560; usdVol schema.usda at 5b3c21a1, lines 614-626"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Both definitions store linear scale and linear 0..1 opacity (CA-B035), but defaults and fields differ: glTF KHR_gaussian_splatting requires a colorSpace string and defaults sortingMethod to cameraDistance, while the OpenUSD usdVol schema defaults sortingModeHint to zDepth and has no colour-space attribute, so a converter that copies defaults changes the declared sort metric and loses colour-space provenance. The glTF README carries an SPDX CC-BY-4.0 header and also a Khronos copyright statement limiting reproduction to the unmodified specification. · locator: KHR_gaussian_splatting README at 7cee0fcd, lines 2-3, 52-54, 64-92, 549-560; usdVol schema.usda at 5b3c21a1, lines 614-626 · source: https://github.com/KhronosGroup/glTF/blob/7cee0fcddd5730e90d488bfb5aa2e52171483dde/extensions/2.0/Khronos/KHR_gaussian_splatting/README.md

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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