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Open USD Standard

Universal Scene Description (USD) is an open-source framework developed by Pixar Animation Studios for the interchange of 3D computer graphics data. It facilitates collaboration, non-destructive editing, and supports multiple views and opinions about graphics data, making it a versatile choice for complex scene management. Wikipedia

For detailed information, you can refer to the official USD documentation: Introduction to USD

Core Properties​

Stage Configuration​

{
  "@context": {
    "@vocab": "https://schema.org/",
    "usd": "https://openusd.org/24.08/spec.html"
  },
  "@type": "Place",
  "name": "Virtual Environment",
  
  "usd:stage": {
    "upAxis": "Y",
    "metersPerUnit": 1.0,
    "timeCodesPerSecond": 24
  }
}

Layer Structure​

{
  "usd:layers": [
    {
      "name": "base",
      "path": "/Environment/Base",
      "defaultPrim": "World"
    },
    {
      "name": "architecture",
      "path": "/Environment/Architecture",
      "reference": "base"
    },
    {
      "name": "furniture",
      "path": "/Environment/Furniture",
      "reference": "architecture"
    }
  ]
}

Variant Sets​

{
  "usd:variants": {
    "lighting": {
      "name": "lighting",
      "variants": ["day", "night", "evening"],
      "default": "day"
    },
    "season": {
      "name": "season",
      "variants": ["summer", "winter", "autumn", "spring"],
      "default": "summer"
    }
  }
}

Complete Example​

{
  "@context": {
    "@vocab": "https://schema.org/",
    "usd": "https://openusd.org/24.08/spec.html"
  },
  "@type": "Place",
  "name": "Virtual Plaza",
  "description": "Interactive public plaza with dynamic lighting and seasonal variations",
  
  "usd:stage": {
    "upAxis": "Y",
    "metersPerUnit": 1.0,
    "timeCodesPerSecond": 24,
    "startTimeCode": 0,
    "endTimeCode": 240
  },
  
  "usd:layers": [
    {
      "name": "base",
      "path": "/Plaza/Base",
      "defaultPrim": "Plaza",
      "kind": "component"
    },
    {
      "name": "terrain",
      "path": "/Plaza/Terrain",
      "reference": "base",
      "kind": "component"
    },
    {
      "name": "architecture",
      "path": "/Plaza/Architecture",
      "reference": "terrain",
      "kind": "assembly"
    },
    {
      "name": "vegetation",
      "path": "/Plaza/Vegetation",
      "reference": "architecture",
      "kind": "component"
    },
    {
      "name": "furniture",
      "path": "/Plaza/Furniture",
      "reference": "architecture",
      "kind": "component"
    },
    {
      "name": "lighting",
      "path": "/Plaza/Lighting",
      "reference": "architecture",
      "kind": "component"
    }
  ],
  
  "usd:variants": {
    "lighting": {
      "name": "lighting",
      "variants": ["day", "night", "evening"],
      "default": "day",
      "properties": {
        "intensity": "float",
        "color": "color3f",
        "direction": "vector3f"
      }
    },
    "season": {
      "name": "season",
      "variants": ["summer", "winter", "autumn", "spring"],
      "default": "summer",
      "affectedLayers": ["vegetation", "lighting"]
    },
    "events": {
      "name": "events",
      "variants": ["normal", "celebration", "concert"],
      "default": "normal",
      "affectedLayers": ["lighting", "furniture"]
    }
  },
  
  "usd:composition": {
    "defaultPrim": "Plaza",
    "primChildren": [
      {
        "name": "Ground",
        "type": "Xform",
        "variants": ["season"]
      },
      {
        "name": "Buildings",
        "type": "Xform",
        "variants": ["lighting"]
      },
      {
        "name": "Trees",
        "type": "Xform",
        "variants": ["season"]
      },
      {
        "name": "Installations",
        "type": "Xform",
        "variants": ["events"]
      }
    ]
  },
  
  "usd:references": [
    {
      "name": "StandardFurniture",
      "path": "/Plaza/Furniture/Standard",
      "assetPath": "furniture/standard.usd"
    },
    {
      "name": "EventFurniture",
      "path": "/Plaza/Furniture/Event",
      "assetPath": "furniture/event.usd"
    }
  ],
  
  "usd:properties": {
    "visibility": "inherited",
    "purpose": "default",
    "kind": "assembly"
  }
}

Property Guidelines​

Stage Properties​

  • Use proper up axis ("Y" or "Z")
  • Define correct scale (metersPerUnit)
  • Specify time codes if animated
  • Include frame rate information

Layer Properties​

  • Use descriptive layer names
  • Define clear layer hierarchy
  • Specify reference relationships
  • Include layer purposes

Variant Properties​

  • Use meaningful variant names
  • Define default variants
  • Specify affected properties
  • Document variant relationships

Composition Rules​

Layer Organization​

  1. Base layers first
  2. Referenced layers follow
  3. Specializations last
  4. Clear dependency chain

Variant Management​

  1. Group related variants
  2. Define fallback options
  3. Document dependencies
  4. Specify affect scope

Best Practices​

  1. Layer Structure

    • Organize layers logically
    • Use clear naming conventions
    • Document layer purposes
    • Maintain clear hierarchy

  2. Variant Sets

    • Group related variations
    • Provide default options
    • Consider performance
    • Document combinations

  3. Reference Management

    • Use clear asset paths
    • Document dependencies
    • Consider load order
    • Manage asset versions

  4. Property Inheritance

    • Define inheritance clearly
    • Document overrides
    • Consider performance
    • Maintain consistency

Common Issues​

  1. Layer Conflicts

    {
      "usd:layers": [
        {
          "name": "override",
          "reference": "missing_layer"  // Invalid reference
        }
      ]
    }

  2. Invalid Variants

    {
      "usd:variants": {
        "lighting": {
          "variants": [],  // Empty variants array
          "default": "missing"  // Non-existent default
        }
      }
    }

Next Steps​