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    1. Home
    2. 3D File Formats
    3. USD

    What's on this Page

      • What is a USD file?
      • USD File Format
        • USD Data Types
      • USD Example
      • References

    What is a USD file?

    A file with .usd extension is a Universal Scene Description file format that encodes data for the purpose of data interchanging and augmenting between digital content creation applications. Developed by Pixar, USD provides the ability to interchange elemental assets (such as models) or animation. USD enables assembly and organization of any number of 3D scene elements such as virtual sets, scenes, and shots to transmit them from application to application. Some of the applciations that can be open USD files include Pixar Animation Studios USD and NVIDIA Omniverse.

    USD File Format

    USD files can have binary format (also known as Crate files) or ASCII-backed files. Both these file formats are interchangeable where the references can be linked to .usd assets without changing the sources. USD consists of a set of C++ libraries with Python bindings for scripting.

    USD Data Types

    The fundamental data types supported by the USD file format are listed in the following table.

    Value type tokenC++ typeDescription
    boolbool
    ucharuint8_t8 bit unsigned integer
    intint32_t32 bit signed integer
    uintuint32_t32 bit unsigned integer
    int64int64_t64 bit signed integer
    uint64uint64_t64 bit unsigned integer
    halfGfHalf16 bit floating point
    floatfloat32 bit floating point
    doubledouble64 bit floating point
    timecodeSdfTimeCodedouble representing a resolvable time
    stringstd::stringstl string
    tokenTfTokeninterned string with fast comparison and hashing
    assetSdfAssetPathrepresents a resolvable path to another asset
    matrix2dGfMatrix2d2x2 matrix of doubles
    matrix3dGfMatrix3d3x3 matrix of doubles
    matrix4dGfMatrix4d4x4 matrix of doubles
    quatdGfQuatddouble-precision quaternion
    quatfGfQuatfsingle-precision quaternion
    quathGfQuathhalf-precision quaternion
    double2GfVec2dvector of 2 doubles
    float2GfVec2fvector of 2 floats
    half2GfVec2hvector of 2 half’s
    int2GfVec2ivector of 2 ints
    double3GfVec3dvector of 3 doubles
    float3GfVec3fvector of 3 floats
    half3GfVec3hvector of 3 half’s
    int3GfVec3ivector of 3 ints
    double4GfVec4dvector of 4 doubles
    float4GfVec4fvector of 4 floats
    half4GfVec4hvector of 4 half’s
    int4GfVec4ivector of 4 ints

    USD Example

    An example of a USD file in plain ASCII file format is as following.

    #usda 1.0
    
    class "_class_Planet"
    {
        bool has_life = False
    }
    
    def Xform "SolarSystem"
    {
        def "Earth" (
            references = @./planet.usda@</Planet>
        )
        {
            bool has_life = True
            string color = "blue"
        }
    
        def "Mars" (
            references = @./planet.usda@</Planet>
        )
        {
            string color = "red"
        }
    
        def "Saturn" (
            references = @./planet.usda@</Planet>
            variants = {
                string rings = "with_rings"
            }
        )
        {
            string color = "beige"
        }
    }
    
    #usda 1.0
    
    class "_class_Planet"
    {
    }
    
    def Sphere "Planet" (
        inherits = </_class_Planet>
        kind = "model"
        variantSets = "rings"
        variants = {
            string rings = "none"
        }
    )
    {
        variantSet "rings" = {
            "none" {
                bool has_rings = False
            }
            "with_rings" {
                bool has_rings = True
            }
        }
    
    }
    

    References

    • Introduction to USD
    • USD API Reference