Universal Scene Description

Importación de archivos USD

USD files typically represent the scene as a hierarchy of primitives, or prims. Individual prims contain data to describe scene entities, such as geometry, lights, cameras and transform hierarchies. Blender’s USD importer converts USD prims to a hierarchy of Blender objects. Like the USD exporter, the importer does not yet handle certain USD composition concepts, such as layers and references.

The following USD data types can be imported as Blender objects:

• Cámaras

• Curvas

• Luces

• Materiales

• Mallas

• Nubes de puntos

• Formas primitivas

• Volúmenes

For more information on how the various data types are handled, see the following descriptions of the Import Options.

Nota

When importing a USDZ archive, it is important to carefully consider the Import Textures option to determine whether and how to copy texture files from the zip archive.

Xform and Scope Primitives

USD provides an Xform prim type, containing transform data, which can be used to represent transform hierarchies and to organize the scene. Such Xform prims are imported as Blender empty objects.

USD also supports Scope primitives, which are entities that do not contain transform data, but which serve to group other element of the scene. Blender doesn’t have an exact counterpart to the concept of a scope, so such primitives are imported as Blender empties located at the origin. This is an imperfect representation, because empty objects have a transform and Scopes do not, but this approach nonetheless helps preserve the structure of the scene hierarchy.

PointInstancer Primitives

USD provides a UsdGeomPointInstancer prim type, containing instances that are scattered on a primitive’s points.

These are imported into Blender as Point Clouds using a Modificador Nodos de geometría and the Nodo Instanciar en puntos.

Animaciones

The importer supports two types of animation:

• Animating transforms: If a USD primitive has time-varying transform data, a Transform Cache constraint will be added to the imported Blender object.

• Animating geometry: Animated mesh, curve, and point cloud geometry is supported by adding a Mesh Sequence Cache modifier to the imported data. Geometry attribute (USD Primvar) animation is supported for all data types which have corresponding Blender equivalents. This includes colors, UVs, velocities, and other generic attribute data. Note that USD file sequences (i.e. a unique file per frame) are not supported.

Materiales

If a USD mesh or geometry subset has a bound material, the importer will assign to the Blender object a material with the same name as the USD material. If a Blender material with the same name already exists in the scene, the existing material may be used, depending on the Material Name Collision option. Otherwise, a new material will be created.

If the USD material has a USD Preview Surface shader source, the Presentación en vistas color, metallic, and roughness are set to the corresponding USD Preview Surface input values.

There is also an Import USD Preview option to convert USD Preview Surface shaders to Blender Principled BSDF shader nodes. This option can be lossy, as it does not yet handle converting all shader settings and types, but it can generate approximate visualizations of the materials.

Orientación del sistema de coordenadas

En caso de que el archivo USD importado utilice el eje Y hacia arriba, se aplicará una rotación automática a los objetos de primer nivel para convertirlos a la orientación usada por Blender (con el eje Z hacia arriba).

Opciones de importación

The following options are available when importing from USD:

General

Máscara de ruta

Import only the subset of the USD scene rooted at the given primitive.

Incluir (o Incluyendo)

Sólo primitivas visibles

Do not import invisible USD primitives. Only applies to primitives with a non-animated visibility attribute. Primitives with animated visibility will always be imported.

Sólo primitivas definidas

When disabled this allows importing USD primitives which are not defined, such as those with an override specifier.

Definir rango de fotogramas

Update the scene’s start and end frame to match those of the USD stage.

Crear colección

Add all imported objects to a new collection.

Rutas relativas

Select the file relative to the blend-file.

Apply Unit Conversion Scale

Scale the scene objects by the USD Stage metersPerUnit value. This scaling is applied in addition to the value specified in the Scale option.

Escala

Value by which to scale the imported objects in relation to the world’s origin.

Escala de intensidad de luces

Permitirá escalar la intensidad de las luces importadas.

Propiedades personalizadas

Comportamiento al importar atributos de USD como Propiedades personalizadas.

Ninguno:

No importar atributos personalizados de USD.

Usuario:

Imports USD attributes in the userProperties namespace as custom properties. The namespace will be stripped from the property names.

Todos los personalizados:

Imports all USD custom attributes as custom properties. Namespaces will be retained in the property names.

Tipos de objeto

Cámaras

Import UsdGeomCamera primitives as Camera Objects (perspective and orthographic).

Curvas

Import UsdGeomBasisCurves primitives as Curves and UsdGeomNurbsCurves as Blender meshes.

Luces

Import lights as Light Objects. Does not currently include cylinder or geometry lights.

World Dome Light

Converts the first discovered UsdLuxDomeLight dome light to a world background shader.

Materiales

Import UsdPreviewSurface materials.

Mallas

Importará primitivas UsdGeomMesh como objetos de tipo Malla.

Volúmenes

Importará recursos OpenVDB UsdVolVolume como objetos de tipo Volumen.

Nubes de puntos

Importará primitivas UsdGeomPoints como Nubes de puntos.

Formas USD

Import USD primitive shapes as Blender meshes. UsdGeomCapsule, UsdGeomCylinder, UsdGeomCone, UsdGeomCube, and UsdGeomSphere are supported.

Display Purpose

Procesar

Incluirá las primitivas marcadas con el propósito Procesamiento (render).

Reemplazo

Incluirá las primitivas marcadas con el propósito Reemplazo (proxy).

Guía

Include primitives with purpose guide.

Propósito del material

Attempt to import materials with the given purpose. If no material with this purpose is bound to the primitive, then the fallback behavior, if any, is noted below.

Todo propósito:

Intentará importar materiales marcados como para todo propósito (allPurpose).

Previsualización:

Intentará importar materiales marcados como para previsualización (preview). Alternativamente importará materiales marcados como para todo propósito (allPurpose).

Completo:

Intentará importar materiales marcados como completos (full). Alternativamente importará materiales marcados como para todo propósito (allPurpose) o previsualización (preview), en ese orden de precedencia.

Geometría

Coordenadas UV

Leerá las coordenadas UV de la malla.

Atributos de color

Convert the USD mesh displayColor values to Blender’s Color Attributes.

Atributos de mallas

Read USD Primvars as mesh attributes.

Subdivisión

Create Subdivision Surface modifiers based on the USD SubdivisionScheme attribute.

Validar mallas

Check the imported mesh for corrupt data and fix it if necessary. When disabled, erroneous data may cause crashes displaying or editing the meshes. This option will make the importing slower but is recommended, as data errors are not always obvious.

Merge parent Xform

Allow USD primitives to merge with their Xform parent if they are the only child in the hierarchy.

Sistemas de control

Formas clave

Imports USD blend shapes as Blender’s Formas clave.

Esqueletos

Imports USD skeletons as Blender’s Esqueletos.

Materiales

Importar todos los materiales

Also import materials that are not used by any geometry. Note, when this option is false, materials referenced by geometry will still be imported.

Importar previsualización USD

Convert USD Preview Surface shaders to Principled BSDF shader networks.

Definir fundido de material

If the Import USD Preview option is enabled, the material blend method will automatically be set based on the opacity and opacityThreshold shader inputs, allowing for visualization of transparent objects.

Colisión de nombres de materiales

Behavior when the name of an imported material conflicts with an existing material.

Hacer único:

Import each USD material as a unique Blender material.

Referenciar existente:

If a material with the same name already exists, reference that instead of importing.

Texturas

When importing a USDZ package, the following options specify whether and how texture asset dependencies of the USD should be copied from the zip archive so they can be loaded into Blender.

Importar texturas

Behavior when importing textures from a USDZ archive.

Ninguno:

Don’t import textures. Note that, with this option, material textures may fail to be resolved in Blender.

Empacadas:

Importará las texturas como datos empacados en el archivo de Blender.

Copiar:

Copy files to the directory specified in the Textures Directory option.

Directorio de texturas

Path to the directory where imported textures will be copied, when the Import Textures mode is Copy.

Note that the default textures directory is the relative path //textures, which requires the Blender file to have been saved before importing, so the relative path can be resolved.

Colisión de nombres de archivo

Behavior when the name of an imported texture file conflicts with an existing file.

Usar existente:

En caso de que ya existiera un archivo con el mismo nombre, éste será usado en vez de copiarlo.

Sobrescribir:

Sobrescribirá los archivos existentes.

Partículas e instanciado

Instancias de la escena

Importará las instancias de la gráfica de la escena USD como instancias de colecciones, en caso contrario serán importadas como copias.

Exportación a archivos USD

Universal Scene Description (USD) files can contain complex layering, overriding, and references to other files. Blender’s USD Exporter takes a much simpler approach. When exporting, all visible, supported objects in the scene are exported, optionally limited by their selection state. Blender does not (yet) support exporting invisible objects, USD layers, variants, etc.

Los siguientes tipos de objetos podrán ser exportados a USD:

• Mallas (de diferentes tipos, ver debajo).

• Cámaras (por el momento sólo cámaras en perspectiva, no las ortogonales).

• Curvas

• Luces

• Pelo (exportado como curvas y limitado a las hebras primarias).

• Nubes de puntos

• Volúmenes

• Esqueletos

When exporting an animation, the final, evaluated mesh is written to USD. This means that the following meshes can be exported:

• Static meshes.

• Deforming meshes; here the topology of the mesh does not change, but the locations of the vertices change over time. Examples are animated characters or bouncing (but not cracking) objects.

• Arbitrarily animated meshes; here the topology does change. An example is the result of a fluid simulation, where splashes of fluid can break off the main body.

• Metaballs are exported as animated meshes.

Nota

To export the Blender scene as a USDZ archive, set the file extension of the output file to .usdz. The exported USDZ package will be a zip archive containing the USD and its texture file dependencies.

Shot from Spring exported to USD and opened in USDView.

Opciones de exportación

The following options are available when exporting to USD:

General

Primitiva de primer nivel

If set, add a transform primitive with the given path to the stage as the parent of all exported data.

Incluir (o Incluyendo)

Sólo lo seleccionado

When checked, only selected objects are exported. Instanced objects, for example collections that are instanced in the scene, are considered “selected” when their instancer is selected.

Sólo objetos visibles

Only exports objects that are not hidden. Invisible parents of exported objects are exported as empty transforms.

Animación

When checked, the entire scene frame range is exported. When unchecked, only the current scene frame is exported.

Datos de Blender

Propiedades personalizadas

Exports Custom Properties as USD attributes. The Namespace property is used to determine the namespace that the attributes are written to.

Espacio de nombres

If set, add the given namespace as a prefix to exported custom property names. This only applies to property names that do not already have a prefix (e.g., it would apply to name bar but not foo:bar) and does not apply to Blender object and data names which are always exported in the userProperties:blender namespace.

By default, userProperties namespace is used.

Nombres de Blender

Author USD custom attributes containing the original Blender object and object data names.

Permitir Unicode

Preserves UTF-8 encoded characters when writing USD prim and property names (requires software utilizing USD 24.03 or greater when opening the resulting files).

Archivos referenciados

Rutas relativas

Use relative paths to reference external files (i.e. textures, volumes) in the exported USD file, otherwise use absolute paths.

Convertir orientación

Convertirá los ejes de orientación a una convención distinta, para que coincida con la de otras aplicaciones. Blender utiliza Y como avance, Z hacia arriba (puesto que la vista frontal mira en dirección al eje +Y). Por ejemplo, es común que las aplicaciones utilicen Y como el eje superior, en ese caso se deberá usar -Z como avance e Y como eje superior.

Eje de avance / superior

By mapping these to different axes you can convert rotations between applications default up and forward axes.

Unidades

Set the USD Stage metersPerUnit metadata to the chosen measurement.

Meters Per Unit

Value to use for metersPerUnit if Custom Units are selected.

Operadores de transformación

The type of transform operators to use to transform prims.

Posición, Rotación, Escala:

Export with translate, rotate, and scale Xform operators.

Posición, Orientación, Escala:

Export with translate, orient quaternion, and scale Xform operators.

Matriz:

Export matrix operator.

Usar opciones de

Determines whether to use Viewport or Render visibility of objects, modifier settings, and other properties providing similar options, during export.

Tipos de objeto

Mallas

Exportará objetos de tipo Malla

Luces

Exports Light Objects The UsdLuxShapingAPI is used to support spot lights.

World Dome Light

Convert the world material to a UsdLuxDomeLight. Currently works for simple materials, consisting of an environment texture connected to a background shader, with an optional vector multiply of the texture color.

Cámaras

Exportará objetos de tipo Cámara. Sólo se exportarán las cámaras de tipo perspectiva.

Curvas

Exportará objetos de tipo Curva

Nubes de puntos

Exports Point Cloud Objects

Volúmenes

Exportará objetos de tipo Volumen

Pelo

Exports parent hair strands are exported as a curve system. Hair strand colors are not exported.

Nota

The corresponding USD schema type used during Export is analagous to the type read during Import. See the Import section for details.

Geometría

Mapas UV

When checked, includes UV coordinates for exported meshes. The name of the UV map in USD is the same as the name in Blender.

Renombrar mapas UV

Exports UV maps using the USD default name (st) as opposed to Blender’s default name (UVMap).

Normales

When checked, includes normals for exported meshes. This includes custom loop normals.

Merge parent Xform

Merge USD primitives with their Xform parent if possible. USD does not allow nested UsdGeomGprims, intermediary Xform prims will be defined to keep the USD file valid when encountering object hierarchies.

Triangular

Triangulates the mesh before writing. For more detail on the specific option see the Triangulate modifier.

Sistemas de control

Formas clave

Export shape keys as USD blend shapes.

Las Formas clave absolutas no son soportadas.

Esqueletos

Export Armatures and meshes with Armature Modifiers as USD skeletons and skinned meshes.

Limitaciones:

• Los modificadores, más allá de los modificadores de Esqueleto, no serán aplicados.

• Los huesos flexibles no son soportados.

Sólo huesos deformantes

Only export deform bones and their parents.

Materiales

Exports material information of the object. By default the exporter approximates the BSDF Principista node tree by converting it to USD’s Preview Surface format.

When a mesh has multiple materials assigned, a geometry subset is created for each material. The first material (if any) is always applied to the mesh itself as well (regardless of the existence of geometry subsets), because the Hydra viewport does not support materials on subsets. See USD issue #542 for more information.

Nota

If USD Preview Surface Network and MaterialX Network are disabled, the material is set to the viewport materials of meshes.

Soporte para desplazamiento

Se soporta el desplazamiento con algunas salvedades:

• Only object space displacement is supported (no vector displacement).

• Midlevel and Scale controls can only be constants.

• MaterialX is currently not supported, see the feature commit for details.

Red de previsualización de superficies USD

Approximates a BSDF Principista node tree by converting it to USD’s Preview Surface format.

Nota

To support opacityThreshold, sometimes known as «Alpha Clip», the node tree must either use a Math node set to Round, if the desired threshold is 0.5, or by using a pair of Math nodes implementing 1 - (value < threshold). The result should be plugged into the Alpha socket on the Principled BSDF node.

Advertencia

Not all nodes are supported; currently only simple node trees containing Diffuse BSDF, Principled BSDF, Image Textures, UVMap, and Separate RGB nodes are supported.

Red MaterialX

Generates material shading graphs using the MaterialX standard. This standard is designed to support a high amount of interoperability among DCCs <Digital Content Creation>. In Blender, MaterialX supports most of the shader nodes and their functionality but has a few caveats (see below).

Precauciones con la implementación

When using the Principled BSDF, the resulting graph is very usable. However, when using some of the other BSDFs, some of the generated shading graphs are difficult for other DCC’s to understand.

Exportar texturas

Método para exportar texturas.

Mantener:

Usar la posición original de las texturas.

Preservar:

Preserve file paths of textures from already imported USD files. Export remaining textures to a “textures” folder next to the USD file.

Nueva ruta:

Export textures to a “textures” folder next to the USD file.

Sobrescribir texturas

Allow overwriting existing texture files when exporting textures.

Reducción muestreo de texturas USDZ

Choose a maximum size for all exported textures.

Mantener:

Mantendrá los tamaños actuales de todas las texturas.

256:

Las redimensionará a un máximo de 256 píxeles.

512:

Las redimensionará a un máximo de 512 píxeles.

1024:

Las redimensionará a un máximo de 1024 píxeles.

2048:

Las redimensionará a un máximo de 2048 píxeles.

4096:

Las redimensionará a un máximo de 4096 píxeles.

Personalizado:

Permitirá especificar un tamaño personalizado.

Tamaño reducción USDZ personalizado

El tamaño en píxeles de la reducción de muestreo Personalizado.

Experimental

Instanciado

As this is an experimental option. When unchecked, duplicated objects are exported as real objects, so a particle system with 100 particles that is displayed with 100 meshes will have 100 individual meshes in the exported file. When checked, duplicated objects are exported as a reference to the original object. If the original object is not part of the export, the first duplicate is exported as real object and used as reference.

Limitaciones del exportador

Mallas de un solo lado y de doble lado

USD seems to support neither per-material nor per-face-group double-sidedness, so Blender uses the flag from the first material to mark the entire mesh as single/double-sided. If there is no material it defaults to double-sided.

Materiales

When there are multiple materials, the mesh faces are stored as geometry subset and each material is assigned to the appropriate subset. If there is only one material this is skipped. Note that the geometry subsets are not time-sampled, so it may break when an animated mesh changes topology.

Pelo

Only the parent strands are exported, and only with a constant color. No UV coordinates, and no information about the normals.

Cámara

Only perspective cameras are exported.

Partículas

Particles are only written when they are alive, which means that they are always visible. There is currently no code that deals with marking them as invisible outside their lifespan.

Objects instanced by particle system are exported by suffixing the object name with the particle’s persistent ID, giving each particle transform a unique name.

Instanciado y referenciamiento

This is still an experimental feature that can be enabled when exporting to USD. When enabled, instanced object meshes are written to USD as references to the original mesh. The first copy of the mesh is written for real, and the following copies are referencing the first. Which mesh is considered “the first” is chosen more or less arbitrarily.

USDZ

Due to a current limitation in the USD library, UDIM textures cannot be include in the USDZ archive. This limitation will likely be addressed in a future version of USD. (See USD pull request #2133.)

USD Primvar data types

Blender supports a subset of the USD basic data types for import and export.

Only the types natively supported by Blender’s attribute system will be processed.

Blender type	USD type	Notas
Booleana	bool
Entero (8 bits)	uchar	The USD unsigned 8-bit value will be cast to a signed value for import. The signed value will be cast to unsigned for export.
Entero	int	A 32-bit signed integer value.
Decimal	decimal de punto flotante	A 32-bit, single-precision, floating point value.
Vector	float3	Vector 3D con valores de 32 bits decimales con punto flotante.
Vector 2D	float2/texCoord2f	2D vector with 32-bit floating-point values.
Color	color4f	RGBA color with 32-bit floating-point values. As a special case, when encountering a Primvar or attribute for USD’s displayColor, it will be read or written as color3f data with an Alpha component of 1.0.
Color (byte)	color4f	USD does not provide a byte color equivalent. The byte values will be converted to float and exported as a color4f.
Cuaternio	quatf	Floating point Quaternion rotation.

Precauciones con la implementación

Blender does not support USD Primvars using 64-bit integer values (int64), those using unsigned types (uint), or those using 64-bit double-precison or 16-bit half-precision floating-point values. For example, this would include such types as matrix4d (4x4 matrix of doubles) and quath (half-precision quaternion).

Nota

The USD float4 data type has no direct Blender equivalent and will not be treated as a Blender Color or Quaternion.