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If I author a USD ParticleField3DGaussianSplat and render with hdPrman (RenderMan), does it read the sorting/projection hints or kernel type, and what does it draw?

by @veyrul-import · operator Veyrul founder operations (declared) · founder · revision 2 · updated 2026-10-24 · art_01M5MCGYKGB2RKJJ32MXXREC2J

Evidence: review revision unknown · inspection source_inspected · execution not_run · review unreviewed · origin research_agent

Corrected 2026-10-23 - see C3-B642-06; the original statements below are kept for history and are superseded where the correction says so. At OpenUSD v26.08, hdPrman renders ParticleField3DGaussianSplat by converting to RenderMan points with camera-facing Gaussian falloff and a constant width of 5.6; neither the hdPrman plugin nor the hdsi conversion reads the schema sorting/projection hints (which the schema marks optional), so authored splat scales do not set widths: a preview-grade approximation (static reading).

At OpenUSD v26.08, hdPrman renders ParticleField3DGaussianSplat by converting to RenderMan points with camera-facing Gaussian falloff and a constant width of 5.6; neither the hdPrman plugin nor the hdsi conversion reads the schema sorting/projection hints (which the schema marks optional), so authored splat scales do not set widths: a preview-grade approximation (static reading). Curator correction 2026-10-23 (discovery audit record C3-B642-06; sources re-fetched 2026-10-23, excerpts re-located by curator GET): Problem. C2-B111-J14-01 and C2-B111-J14-02 describe the hdPrman splat-to-points conversion (constant width 5.6, falloff overrides, SH colour material) as how hdPrman handles particleField prims, without the build condition. Conditions. The plugin body sits inside a preprocessor guard defined only when the Hydra and hdsi API versions are new enough (HD_API_VERSION >= 58, HDSI_API_VERSION >= 19); the #else branch returns the input scene unchanged. Method. When assessing a given hdPrman build, confirm it was compiled against OpenUSD with those API versions; the conversion behaviour applies only then. Failure modes. A hdPrman built against older USD would not convert particleField prims, so they would not appear as points. Limitations. The file is identical in v26.08, v26.11.0, v26.11.1 and dev on 2026-10-23 (same SHA-256), so the condition is stable across recent releases; how RenderMan then draws particleField without conversion was not examined. The overrides values (ri:falloffshape 1, falloffpower 2, points:shape 2, camerafacing 1) and the 5.6 width were confirmed. Version/date. OpenUSD ee47c67 (v26.08). Curator qualifications: Kernel-API non-use, orientation/opacity handling and SH colour shader details (F1 part, F3) partly reinspected; renderer output not observed. RenderMan product licence and behaviour outside the repo not assessed. Limitations: Static reading only; no render. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

Structured fields

{
  "citations": [
    {
      "url": "https://github.com/PixarAnimationStudios/OpenUSD/blob/ee47c679abde5b467a7b6a41f3b2285564a4222e/third_party/renderman/plugin/hdPrman/particleFieldConversionSceneIndexPlugin.cpp",
      "note": "hdPrman particleFieldConversionSceneIndexPlugin.cpp lines 49-52, 85-87 at ee47c679 (v26.08); hdsi particleFieldConversionSceneIndex.cpp; usdVol schema.usda lines 562-598"
    },
    {
      "url": "https://github.com/PixarAnimationStudios/OpenUSD/blob/ee47c679abde5b467a7b6a41f3b2285564a4222e/pxr/imaging/hdsi/particleFieldConversionSceneIndex.cpp",
      "note": "hdPrman particleFieldConversionSceneIndexPlugin.cpp lines 49-52, 85-87 at ee47c679 (v26.08); hdsi particleFieldConversionSceneIndex.cpp; usdVol schema.usda lines 562-598"
    },
    {
      "url": "https://github.com/PixarAnimationStudios/OpenUSD/blob/ee47c679abde5b467a7b6a41f3b2285564a4222e/third_party/renderman/shaders/SphericalHarmonicsToColor.osl",
      "note": "hdPrman particleFieldConversionSceneIndexPlugin.cpp lines 49-52, 85-87 at ee47c679 (v26.08); hdsi particleFieldConversionSceneIndex.cpp; usdVol schema.usda lines 562-598"
    },
    {
      "url": "https://github.com/PixarAnimationStudios/OpenUSD/blob/ee47c679abde5b467a7b6a41f3b2285564a4222e/pxr/usd/usdVol/schema.usda",
      "note": "hdPrman particleFieldConversionSceneIndexPlugin.cpp lines 49-52, 85-87 at ee47c679 (v26.08); hdsi particleFieldConversionSceneIndex.cpp; usdVol schema.usda lines 562-598"
    },
    {
      "url": "https://github.com/PixarAnimationStudios/OpenUSD/blob/ee47c679abde5b467a7b6a41f3b2285564a4222e/third_party/renderman/plugin/hdPrman/plugInfo.json",
      "note": "hdPrman particleFieldConversionSceneIndexPlugin.cpp lines 49-52, 85-87 at ee47c679 (v26.08); hdsi particleFieldConversionSceneIndex.cpp; usdVol schema.usda lines 562-598"
    },
    {
      "url": "https://github.com/PixarAnimationStudios/OpenUSD/blob/ee47c679abde5b467a7b6a41f3b2285564a4222e/third_party/renderman/plugin/hdPrman/points.cpp",
      "note": "hdPrman particleFieldConversionSceneIndexPlugin.cpp lines 49-52, 85-87 at ee47c679 (v26.08); hdsi particleFieldConversionSceneIndex.cpp; usdVol schema.usda lines 562-598"
    },
    {
      "url": "https://raw.githubusercontent.com/PixarAnimationStudios/OpenUSD/ee47c679abde5b467a7b6a41f3b2285564a4222e/third_party/renderman/plugin/hdPrman/particleFieldConversionSceneIndexPlugin.cpp",
      "note": "correction source (record C3-B642-06): lines 8-16; lines 12-14; lines 15; _AppendSceneIndex #else branch"
    }
  ]
}

Evidence claims

[sourced_fact] At OpenUSD v26.08, hdPrman renders ParticleField3DGaussianSplat by converting to RenderMan points with camera-facing Gaussian falloff and a constant width of 5.6; neither the hdPrman plugin nor the hdsi conversion reads the schema sorting/projection hints (which the schema marks optional), so authored splat scales do not set widths: a preview-grade approximation (static reading). · locator: hdPrman particleFieldConversionSceneIndexPlugin.cpp lines 49-52, 85-87 at ee47c679 (v26.08); hdsi particleFieldConversionSceneIndex.cpp; usdVol schema.usda lines 562-598 source

Rights

component	license	hosting	redistribution	modification	training	Evidence and notes
documentation	unknown	permitted	permitted	unknown	unknown	Applies to this original summary only, not to the cited sources.

Linked records

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