OpenUSD 3D Gaussian Splatting Plugins

OpenUSD file-format plugins that import 3D Gaussian Splatting assets as standard USD stages: open a trained .ply, a Niantic .spz, or a PlayCanvas .sog capture directly in usdview or any USD pipeline as OpenUSD 26.05's ParticleField3DGaussianSplat schema.

A Gaussian PLY imported by this plugin and displayed in usdview by a Hydra renderer that supports the OpenUSD particle-field Gaussian schema.

usdview screenshots

These previews show the three supported input formats displayed through the OpenUSD hdParticleField example delegate:

PLY	SOG	SPZ

What it does

• Read-only import of Graphdeco-style Gaussian PLY (ASCII and binary little-endian, SH degrees 0-3) into /Asset/Splat with positions, scales, orientations, opacities, and spherical-harmonic radiance.
• Read-only import of Niantic SPZ (container versions 1-3, SH degrees 0-3), dequantized and converted into the same /Asset/Splat stage.
• Read-only import of PlayCanvas SOG v2 (SH degrees 0-3) in both layouts — the bundled .sog ZIP archive and an unbundled meta.json with its companion lossless-WebP property planes — decoded from codebooks and image planes into the same stage. All three formats author the identical hierarchy, schema, and metadata through one shared writer.
• Header-only metadata reads (~5 ms at any size), PLY import arguments (shDegree, opacityThreshold, scaleMultiplier), and stable GSPLY-**** / GSPZ-**** / GSSOG-**** diagnostics with machine-readable catalogs.
• Import only — rendering is owned by the sibling project hydra-merlin.

What it reads

gaussian-ply — Graphdeco-style .ply:

Exporter	Status
Graphdeco reference (INRIA)	✅ verified (Mip-NeRF 360 garden, 5.8M Gaussians)
Brush	✅ verified (committed CC0 corpus)
Jawset Postshot	✅ verified (up to 1.9M Gaussians)
SuperSplat uncompressed export	☑ layout-compatible, fixture-covered
SuperSplat compressed .ply, .splat, .ksplat	❌ rejected explicitly (details)

gaussian-spz — Niantic .spz:

Container	Status
SPZ versions 1-3 (gzip)	✅ decoded, fixture-covered, and verified against a committed CC0 real-asset corpus
SPZ version 4 (ZSTD)	❌ rejected with a specific unsupported-version diagnostic

gaussian-sog — PlayCanvas .sog / meta.json:

Container	Status
SOG v2, bundled .sog (ZIP)	✅ decoded, fixture-covered, and verified against a committed CC0 real-asset corpus
SOG v2, unbundled meta.json + .webp planes	✅ decoded through the asset resolver, fixture-covered
SOG v1 (per-channel mins/maxs, no version)	❌ rejected with a specific unsupported-version diagnostic
Streamed SOG (lod-meta.json, LOD chunks)	❌ not read; a later SOG milestone
Lossy WebP property planes	❌ rejected rather than decoded approximately

Full tables: dialect compatibility · capability matrix · performance baselines.

Install a binary release

For the shortest package-consumer path, choose the v0.5.1 product archive that matches the host platform, the cy2026 OpenUSD runtime, and Python 3.13:

usd-3dgs-plugins-0.5.1-cy2026-windows-x86_64-py313-usd-plugin-product.tar.zst
usd-3dgs-plugins-0.5.1-cy2026-macos-arm64-py313-usd-plugin-product.tar.zst
usd-3dgs-plugins-0.5.1-cy2026-linux-x86_64-py313-usd-plugin-product.tar.zst

Extract the target archive, then point PXR_PLUGINPATH_NAME at the extracted plugin/resources/gaussian-ply, gaussian-spz, and gaussian-sog directories. Use ; between paths on Windows and : on macOS/Linux; keep the extracted lib directory on the platform library path. Open one file from each format with usdcat to check plugin discovery:

$package = "C:\path\to\extracted"
$env:PXR_PLUGINPATH_NAME = "$package\plugin\resources\gaussian-ply;$package\plugin\resources\gaussian-spz;$package\plugin\resources\gaussian-sog"
$env:Path = "$package\lib;$env:Path"
usdcat --flatten --out scene-ply.usda scene.ply
usdcat --flatten --out scene-spz.usda scene.spz
usdcat --flatten --out scene-sog.usda scene.sog

The exact extraction layout can vary between the aggregate product and a standalone member package; use the corresponding member root for each resource directory. The detailed activation steps, checksum guidance, and the unbundled SOG example are in INSTALL.md. Stock usdview can open the stage and inspect /Asset/Splat, but visible splats still require a Gaussian-capable Hydra delegate.

Quick start

Requirements: OpenUSD >=26.05,<27.0 and a C++17 compiler. Build and test with plain CMake against an OpenUSD installation in that range:

cmake --preset default -DCMAKE_PREFIX_PATH=/path/to/openusd
cmake --build --preset default
ctest --test-dir build/default --output-on-failure

The repo is dual-mode: with OpenStrata ost 0.22.10 the same tree gets the full verification ladder, packaging, and viewer tooling — see BUILDING.md:

ost runtime pull cy2026 --profile usd
ost plugin build plugins/gaussian-ply
ost plugin test plugins/gaussian-ply --up-to 5

Open a capture in usdview:

ost plugin view plugins\gaussian-ply "C:\path\to\scene.ply"

Seeing the splats needs a Gaussian-capable Hydra renderer. These plugins import; they do not render. Stock usdview opens the stage and shows the /Asset/Splat hierarchy and its attributes, but draws nothing, because no default Hydra delegate understands ParticleField3DGaussianSplat. For a visual preview today, use the OpenUSD hdParticleField example delegate — that is what the animation above shows. Production rendering is the job of the sibling project hydra-merlin.

Or convert it to a compact binary USD file:

ost plugin run plugins\gaussian-ply -- usdcat --flatten --skipSourceFileComment --usdFormat usdc --out scene.usd scene.ply

Installing a packaged release into an existing OpenUSD environment is covered in INSTALL.md.

Status

v0.5.1 — release polish and hostile-input hardening — is released. (release record).

v0.4.0 turned the decoder-to-USD seam PLY and SPZ share into a normative, enforced contract: shared semantic validation and overflow-checked size math, a stage-free decoder test kit, an import-statistics seam, and a documented header/API boundary. It also corrected authored orientation to RUB / Y-up (ADR 0001) to match the upAxis every stage already declared; that is a pre-1.0 change to v0.1.0-v0.3.0 output, so re-import to update.

v0.5.0 is the first format added on top of that contract: gaussian-sog reads SOG v2 in both layouts, targets the shared model with no format-specific USD authoring, and joins the cross-format equivalence triples. Releases are tag-driven and digest-reproducible (release records).

Architecture

.ply       -> PlyReader (tinyPLY adapter)     -> GaussianPlyDecoder --+
.spz       -> SpzReader (miniz DEFLATE/gzip)  -> GaussianSpzDecoder --+
.sog    \                                                            |
         -> SogReader (miniz ZIP + libwebp    -> GaussianSogDecoder --+
meta.json/     lossless property planes)                             |
                                                                     v
                        GaussianCloudData (gaussianCore; no USD types)
                        -> GaussianLayerWriter (libs/gaussian-usd)
                        -> UsdVolParticleField3DGaussianSplat

The workspace separates format-independent Gaussian modelling (libs/gaussian-core) and shared USD authoring (libs/gaussian-usd) from format-specific import (plugins/gaussian-ply, plugins/gaussian-spz, plugins/gaussian-sog), each independently buildable and testable. It is built, tested, packaged, and released with OpenStrata's ost CLI (measured usage: dogfooding reports) and remains dual-mode with plain CMake. The sibling project usd-vrm-plugins shares this layout and process. Policy: DESIGN_POLICY.md.

Contributing and documentation

The minimal development path is in CONTRIBUTING.md; the documentation index is docs/README.md. The normative mapping contracts are PLY_MAPPING.md, SPZ_MAPPING.md, and SOG_MAPPING.md.

License

Project code is Apache-2.0. SPZ and SOG are implemented from their publishers' open specifications and MIT-licensed reference toolchains rather than vendored; only container mechanics use libraries. Third-party retained notices and fixed source revisions (tinyPLY, miniz, libwebp) are documented in THIRD_PARTY_NOTICES.md.