Readme.md

Common Plug-in Commands

This read-me documents the common commands that are shared by the various USD plug-ins made by Autodesk and Pixar.

Common Plug-in Contents

The common parts of Maya USD plug-in provides base commands to import and export USD files from scripts. The name of the command as seen by the end-user will vary for each specific plug-in. In the following table, we give an example of what the final command name would be in Maya, in this instance for the mayaUsd plug-in.

Class Name	Example Real Cmd Name	Purpose
MayaUSDImportCommand	mayaUSDImport	Command to import from a USD file
MayaUSDExportCommand	mayaUSDExport	Command to export into a USD file
MayaUSDListShadingModesCommand	mayaUSDListShadingModes	Command to get available shading modes
EditTargetCommand	mayaUsdEditTarget	Command to set or get the edit target
LayerEditorCommand	mayaUsdLayerEditor	Manipulate layers
LayerEditorWindowCommand	mayaUsdLayerEditorWindow	Open or manipulate the layer window
SchemaCommand	mayaUsdSchema	Manipulate prim schemas

Each base command class is documented in the following sections.

MayaUSDImportCommand

Command Flags

Long flag	Short flag	Type	Default	Description
-apiSchema	-api	string (multi)	none	Imports the given API schemas' attributes as Maya custom attributes. This only recognizes API schemas that have been applied to prims on the stage. The attributes will properly round-trip if you re-export back to USD.
-chaser	-chr	string(multi)	none	Specify the import chasers to execute as part of the import. See "Import Chasers" below.
-chaserArgs	-cha	string[3] multi	none	Pass argument names and values to import chasers. Each argument to -chaserArgs should be a triple of the form: (<chaser name>, <argument name>, <argument value>). See "Import Chasers" below.
-excludePrimvar	-epv	string (multi)	none	Excludes the named primvar(s) from being imported as color sets or UV sets. The primvar name should be the full name without the primvars: namespace prefix.
-excludePrimvarNamespace	-epv	string (multi)	none	Excludes the named primvar namespace(s) from being imported as color sets or UV sets. The namespance should be the name without the primvars: namespace prefix. Ex: primvars:excludeNamespace:excludeMe:excludeMetoo can be excluded by specifying excludeNamespace or excludeNamespace:excludeMe
-excludeExportTypes	-eet	string (multi)	none	Excludes the selected types of prims from being exported. The options are: Meshes, Cameras and Lights.
-file	-f	string	none	Name of the USD being loaded
-frameRange	-fr	float float	none	The frame range of animations to import
-importInstances	-ii	bool	true	Import USD instanced geometries as Maya instanced shapes. Will flatten the scene otherwise.
-jobContext	-jc	string (multi)	none	Specifies an additional import context to handle. These usually contains extra schemas, primitives, and materials that are to be imported for a specific task, a target renderer for example.
-metadata	-md	string (multi)	hidden, instanceable, kind	Imports the given USD metadata fields as Maya custom attributes (e.g. USD_hidden, USD_kind, etc.) if they're authored on the USD prim. The metadata will properly round-trip if you re-export back to USD.
-parent	-p	string	none	Name of the Maya scope that will be the parent of the imported data.
-primPath	-pp	string	none (defaultPrim)	Name of the USD scope where traversing will being. The prim at the specified primPath (including the prim) will be imported. Specifying the pseudo-root (/) means you want to import everything in the file. If the passed prim path is empty, it will first try to import the defaultPrim for the rootLayer if it exists. Otherwise, it will behave as if the pseudo-root was passed in.
-preferredMaterial	-prm	string	lambert	Indicate a preference towards a Maya native surface material for importers that can resolve to multiple Maya materials. Allowed values are none (prefer plugin nodes like pxrUsdPreviewSurface and aiStandardSurface) or one of lambert, standardSurface, blinn, phong. In displayColor shading mode, a value of none will default to lambert.
-primVariant	-pv	string (multi)	none	Specifies variant choices to be imported on a prim. The variant specified will be the one to be imported, otherwise, the default variant will be imported. This flag is repeatable. Repeating the flag allows for extra prims and variant choices to be imported.
-readAnimData	-ani	bool	false	Read animation data from prims while importing the specified USD file. If the USD file being imported specifies startTimeCode and/or endTimeCode, Maya's MinTime and/or MaxTime will be expanded if necessary to include that frame range. Note: Only some types of animation are currently supported, for example: animated visibility, animated transforms, animated cameras, mesh and NURBS surface animation via blend shape deformers. Other types are not yet supported, for example: time-varying curve points, time-varying mesh points/normals, time-varying NURBS surface points
-remapUVSetsTo	-ruv	string2	none	Specify UV sets by name to rename on import. Each argument should be a pair of the form: (<from set name>, <to set name>).
-shadingMode	-shd	string[2] multi	useRegistry UsdPreviewSurface	Ordered list of shading mode importers to try when importing materials. The search stops as soon as one valid material is found. Allowed values for the first parameter are: none (stop search immediately, must be used to signal no material import), displayColor (if there are bound materials in the USD, create corresponding Lambertian shaders and bind them to the appropriate Maya geometry nodes), pxrRis (attempt to reconstruct a Maya shading network from (presumed) Renderman RIS shading networks in the USD), useRegistry (attempt to reconstruct a Maya shading network from (presumed) UsdShade shading networks in the USD) the second item in the parameter pair is a convertMaterialFrom flag which allows specifying which one of the registered USD material sources to explore. The full list of registered USD material sources can be found via the mayaUSDListShadingModesCommand command.
-useAsAnimationCache	-uac	bool	false	Imports geometry prims with time-sampled point data using a point-based deformer node that references the imported USD file. When this parameter is enabled, MayaUSDImportCommand will create a pxrUsdStageNode for the USD file that is being imported. Then for each geometry prim being imported that has time-sampled points, a pxrUsdPointBasedDeformerNode will be created that reads the points for that prim from USD and uses them to deform the imported Maya geometry. This provides better import and playback performance when importing time-sampled geometry from USD, and it should reduce the weight of the resulting Maya scene since it will bypass creating blend shape deformers with per-object, per-time sample geometry. Only point data from the geometry prim will be computed by the deformer from the referenced USD. Transform data from the geometry prim will still be imported into native Maya form on the Maya shape's transform node. Note: This means that a link is created between the resulting Maya scene and the USD file that was imported. With this parameter off (as is the default), the USD file that was imported can be freely changed or deleted post-import. With the parameter on, however, the Maya scene will have a dependency on that USD file, as well as other layers that it may reference. Currently, this functionality is only implemented for Mesh prims/Maya mesh nodes.
-verbose	-v	noarg	false	Make the command output more verbose.
-variant	-var	string[2]	none	Set variant key value pairs
-importUSDZTextures	-itx	bool	false	Imports textures from USDZ archives during import to disk. Can be used in conjuction with -importUSDZTexturesFilePath to specify an explicit directory to write imported textures to. If not specified, requires a Maya project to be set in the current context.
-importUSDZTexturesFilePath	-itf	string	none	Specifies an explicit directory to write imported textures to from a USDZ archive. Has no effect if -importUSDZTextures is not specified.
-importRelativeTextures	-rtx	string	none	Selects how textures filenames are generated: absolute, relative, automatic or none. When automatic, the filename is relative if the source filename of the texture being imported is relative. When none, the file path is left alone, for backward compatible behavior.
-upAxis	-upa	bool	true	Enable changing axis on import.
-unit	-unt	bool	true	Enable changing units on import.
-axisAndUnitMethod	-aum	string	rotateScale	Selects how the unit and axis are handled during import.

Return Value

MayaUSDImportCommand will return an array containing the fullDagPath of the highest prim(s) imported. This is generally the fullDagPath that corresponds to the imported primPath but could be multiple paths if primPath="/".

Repeatable flags

The -primVar flag can be used multiple times when used to import specific variants. In MEL, this simply means using the flag repeatedly for each prim that contains the chosen variants. In Python, the flag requires a string array to import. Importing multiple variant choices using python would for example use:

cmds.mayaUSDImport(
    file='/tmp/test.usda',
    primVariant= [
("/primPath/prim_1", "VariantGroup", "Variant_1"),
("/primPath/prim_2", "VariantGroup", "Variant_2")])

Import behaviours

Import Chasers

Import chasers are plugins that run after the initial import process and can implement post-processing on Maya nodes that executes right after the main import operation is complete. This can be used, for example, to implement pipeline-specific operations and/or early prototyping of features that might otherwise not make sense to be part of the mainline codebase.

Chasers are registered with a particular name and can be passed argument name/value pairs in an invocation of mayaUSDImport. There is no "plugin discovery" method here – the developer/user is responsible for making sure the chaser is registered via a call to the convenience macro USDMAYA_DEFINE_IMPORT_CHASER_FACTORY(name, ctx), where name is the name of the chaser being created. Unlike export chasers, import chasers also have the ability to define Undo and Redo methods in order to allow the mayaUSDImport command to remain compliant with the Maya undo stack. It's not necessary to compile your chaser plugin together with mayaUsdPlugin in order to work; you can create a completely separate maya DLL that contains the business logic of your chaser code, and just call the aforementioned USDMAYA_DEFINE_IMPORT_CHASER_FACTORY to register it, as long as the mayaUsdPlugin DLL is loaded first.

A sample import chaser, infoImportChaser.cpp, is provided to give an example of how to write an import chaser. All it does is read any custom layer data in the USD file on import, and create string attributes on the nodes created and populate them with said string attribute. Invoking it during import is as simple as calling:

cmds.mayaUSDImport(
    file='/tmp/test.usda',
    chaser=['info'])

As mentioned, when writing an import chaser, you also have the chance to implement undo/redo functionality for it in a way that will remain compatible with the Maya undo stack. While you do not have to strictly do this, it is recommended that you keep a record of edits you have made in your chaser and implement the necessary undo/redo functionality where possible or risk experiencing issues (i.e. the main import created a node while your import chaser deleted it from the scene, and then invoking an undo causes a crash since the main plugin's Undo code will no longer work correctly.) It is also highly recommended that you be very mindful of the edits you are making to the scene graph, and how multiple import chasers might work together in unexpected ways or have inter-dependencies.

PostImport function provides access to the SDF paths of USD objects and the DAG paths of imported Maya objects. Input parameter dagPaths and sdfPaths represent the corresponding DAG and SDF paths for the top primitives. To access the mapping between SDF and DAG paths of all primitives, you can use the GetSdfToDagMap() function, which returns a MSdfToDagMap object with SDF path as the key and DAG path as the value. Input parameter stage contains information of all primitives in the current stage. Use TraverseAll() to traverse the primitives.

Import chasers may also be written to parse an array of 3 string arguments for their own purposes, similar to the Alembic export chaser example.

MayaUSDExportCommand

Command Flags

Long flag	Short flag	Type	Default	Description
-apiSchema	-api	string (multi)	none	Exports the given API schema. Requires registering schema exporters for the API.
-append	-a	bool	false	Appends into an existing USD file
-chaser	-chr	string(multi)	none	Specify the export chasers to execute as part of the export. See "Export Chasers" below.
-chaserArgs	-cha	string3	none	Pass argument names and values to export chasers. Each argument to -chaserArgs should be a triple of the form: (<chaser name>, <argument name>, <argument value>). See "Export Chasers" below.
-convertMaterialsTo	-cmt	string(multi)	UsdPreviewSurface	Selects how to convert materials on export. The default value UsdPreviewSurface will export to a UsdPreviewSurface shading network. A plugin mechanism allows more conversions to be registered. Use the mayaUSDListShadingModesCommand command to explore the possible options.
-remapUVSetsTo	-ruv	string2	none	Specify UV sets by name to rename on export. Each argument should be a pair of the form: (<from set name>, <to set name>). This option takes priority over -preserveUVSetNames for any specified UV set.
-compatibility	-com	string	none	Specifies a compatibility profile when exporting the USD file. The compatibility profile may limit features in the exported USD file so that it is compatible with the limitations or requirements of third-party applications. Currently, there are only two profiles: none - Standard export with no compatibility options, appleArKit - Ensures that exported usdz packages are compatible with Apple's implementation (as of ARKit 2/iOS 12/macOS Mojave). Packages referencing multiple layers will be flattened into a single layer, and the first layer will have the extension .usdc. This compatibility profile only applies when exporting usdz packages; if you enable this profile and don't specify a file extension in the -file flag, the .usdz extension will be used instead.
-defaultCameras	-dc	noarg	false	Export the four Maya default cameras
-defaultMeshScheme	-dms	string	catmullClark	Sets the default subdivision scheme for exported Maya meshes, if the USD_ATTR_subdivisionScheme attribute is not present on the Mesh. Valid values are: none, catmullClark, loop, bilinear
-exportDisplayColor	-dsp	bool	false	Export display color
-jobContext	-jc	string (multi)	none	Specifies an additional export context to handle. These usually contains extra schemas, primitives, and materials that are to be exported for a specific task, a target renderer for example.
-defaultUSDFormat	-duf	string	usdc	The exported USD file format, can be usdc for binary format or usda for ASCII format.
-exportBlendShapes	-ebs	bool	false	Enable or disable export of blend shapes
-exportCollectionBasedBindings	-cbb	bool	false	Enable or disable export of collection-based material assigments. If this option is enabled, export of material collections (-mcs) is also enabled, which causes collections representing sets of geometry with the same material binding to be exported. Materials are bound to the created collections on the prim at materialCollectionsPath (specfied via the -mcp option). Direct (or per-gprim) bindings are not authored when collection-based bindings are enabled.
-exportColorSets	-cls	bool	true	Enable or disable the export of color sets
-exportMaterials	-mat	bool	true	Enable or disable the export of materials
-exportAssignedMaterials	-ama	bool	true	Export materials only if they are assigned to a mesh
-legacyMaterialScope	-lms	bool	false	Export materials under a scope determined using the same algorithm as MayaUSD circa 0.28
-exportInstances	-ein	bool	true	Enable or disable the export of instances
-referenceObjectMode	-rom	string	none	Determines how to export reference objects for meshes. The reference object's points are exported as a primvar on the mesh object; the primvar name is determined by querying UsdUtilsGetPrefName(), which defaults to pref. Valid values are: none - No reference objects are exported, attributeOnly - Only meshes set with a valid "referenceObject" attached will be exported, defaultToMesh - Meshes with no "referenceObject" attached will export their own points
-exportRefsAsInstanceable	-eri	bool	false	Will cause all references created by USD reference assembly nodes or explicitly tagged reference nodes to be set to be instanceable (UsdPrim::SetInstanceable(true)).
-exportRoots	-ert	string	none	Multi-flag that allows export of any DAG subtree without including parents
-exportSkels	-skl	string	none	Determines how to export skeletons. Valid values are: none - No skeleton are exported, auto - All skeletons will be exported, SkelRoots may be created, explicit - only those under SkelRoots
-exportSkin	-skn	string	none	Determines how to export skinClusters via the UsdSkel schema. On any mesh where skin bindings are exported, the geometry data is the pre-deformation data. On any mesh where skin bindings are not exported, the geometry data is the final (post-deformation) data. Valid values are: none - No skinClusters are exported, auto - All skinClusters will be exported for non-root prims. The exporter errors on skinClusters on any root prims. The rootmost prim containing any skinned mesh will automatically be promoted into a SkelRoot, e.g. if </Model/Mesh> has skinning, then </Model> will be promoted to a SkelRoot, explicit - Only skinClusters under explicitly-tagged SkelRoot prims will be exported. The exporter errors if there are nested SkelRoots. To explicitly tag a prim as a SkelRoot, specify a USD_typeNameattribute on a Maya node.
-exportUVs	-uvs	bool	true	Enable or disable the export of UV sets
-exportRelativeTextures	-rtx	string	automatic	Selects how textures filenames are generated: absolute, relative or automatic. When automatic, the filename is relative if the source filename of the texture being exported is relative
-exportVisibility	-vis	bool	true	Export any state and animation on Maya visibility attributes
-exportComponentTags	-tag	bool	true	Export component tags
-exportStagesAsRefs	-sar	bool	true	Export USD stages as USD references
-exportMaterialCollections	-mcs	bool	false	Create collections representing sets of Maya geometry with the same material binding. These collections are created in the material: namespace on the prim at the specified materialCollectionsPath (see export option -mcp). These collections are encoded using the UsdCollectionAPI schema and are authored compactly using the API UsdUtilsCreateCollections().
-eulerFilter	-ef	bool	false	Exports the euler angle filtering that was performed in Maya
-filterTypes	-ft	string (multi)	none	Maya type names to exclude when exporting. If a type is excluded, all inherited types are also excluded, e.g. excluding surfaceShape will exclude mesh as well. When a node is excluded based on its type name, its subtree hierarchy will be pruned from the export, and its descendants will not be exported.
-file	-f	string		The name of the file being exported. The file format used for export is determined by the extension: (none): By default, adds .usd extension and uses USD's crate (binary) format, .usd: usdc (binary) format, .usda: usda (ASCII), format, .usdc: usdc (binary) format, .usdz: usdz (packaged) format. This will also package asset dependencies, such as textures and other layers, into the usdz package. See -compatibility flag for more details.
-frameRange	-fr	double[2]	[1, 1]	Sets the first and last frame for an anim export (inclusive).
-frameSample	-fs	double (multi)	0.0	Specifies sample times used to multi-sample frames during animation export, where 0.0 refers to the current time sample. This is an advanced option; chances are, you probably want to set the frameStride parameter instead. But if you really do need fine-grained control on multi-sampling frames, see "Frame Samples" below.
-frameStride	-fst	double	1.0	Specifies the increment between frames during animation export, e.g. a stride of 0.5 will give you twice as many time samples, whereas a stride of 2.0 will only give you time samples every other frame. The frame stride is computed before the frame samples are taken into account. Note: Depending on the frame stride, the last frame of the frame range may be skipped. For example, if your frame range is [1.0, 3.0] but you specify a stride of 0.3, then the time samples in your USD file will be 1.0, 1.3, 1.6, 1.9, 2.2, 2.5, 2.8, skipping the last frame time (3.0).
-ignoreWarnings	-ign	bool	false	Ignore warnings, do not fail to export due to warnings
-includeEmptyTransforms	-iet	bool	true	Include Xform even if all they contain are other empty Xforms.
-kind	-k	string	none	Specifies the required USD kind for root prims in the scene. (Does not affect kind for non-root prims.) If this flag is non-empty, then the specified kind will be set on any root prims in the scene without a USD_kind attribute (see the "Maya Custom Attributes" table below). Furthermore, if there are any root prims in the scene that do have a USD_kind attribute, then their USD_kind values will be validated to ensure they are derived from the kind specified by the -kind flag. For example, if the -kind flag is set to group and a root prim has USD_kind=assembly, then this is allowed because assembly derives from group. However, if the root prim has USD_kind=subcomponent instead, then MayaUSDExportCommand would stop with an error, since subcomponent does not derive from group. The validation behavior understands custom kinds that are registered using the USD kind registry, in addition to the built-in kinds.
-disableModelKindProcessor	-dmk	bool	false	Disables the tagging of prim kinds based on the ModelKindProcessor.
-materialCollectionsPath	-mcp	string	none	Path to the prim where material collections must be exported.
-melPerFrameCallback	-mfc	string	none	Mel function called after each frame is exported
-melPostCallback	-mpc	string	none	Mel function called when the export is done
-materialsScopeName	-msn	string	Looks	Materials Scope Name
-mergeTransformAndShape	-mt	bool	true	Combine Maya transform and shape into a single USD prim that has transform and geometry, for all "geometric primitives" (gprims). This results in smaller and faster scenes. Gprims will be "unpacked" back into transform and shape nodes when imported into Maya from USD.
-writeDefaults	-wd	bool	false	Write default attribute values at the default USD time.
-normalizeNurbs	-nnu	bool	false	When setm the UV coordinates of nurbs are normalized to be between zero and one.
-preserveUVSetNames	-puv	bool	false	Refrain from renaming UV sets additional to "map1" to "st1", "st2", etc. This option is overridden for any UV set specified in -remapUVSetsTo.
-pythonPerFrameCallback	-pfc	string	none	Python function called after each frame is exported
-pythonPostCallback	-ppc	string	none	Python function called when the export is done
-parentScope	-psc	string	none	Deprecated. Use -rootPrim instead. Name of the USD scope that is the parent of the exported data
-defaultPrim	-dp	string	none	Set the default prim on export. If passed n empty string, then no default prim is used. If the flag is absent, the first root prim is set as the default prim.
-rootPrim	-rpm	string	none	Name of the USD root prim that is the parent of the exported data
-rootPrimType	-rpt	string	none	Type of the USD root prim. Currently Scope and Xform are supported.
-renderableOnly	-ro	noarg		When set, only renderable prims are exported to USD.
-renderLayerMode	-rlm	string	defaultLayer	Specify which render layer(s) to use during export. Valid values are: defaultLayer: Makes the default render layer the current render layer before exporting, then switches back after. No layer switching is done if the default render layer is already the current render layer, currentLayer: The current render layer is used for export and no layer switching is done, modelingVariant: Generates a variant in the modelingVariant variantSet for each render layer in the scene. The default render layer is made the default variant selection.
-shadingMode	-shd	string	useRegistry	Set the shading schema to use. Valid values are: none: export no shading data to the USD, pxrRis: export the authored Maya shading networks, applying the same translations applied by RenderMan for Maya to the shader types, useRegistry: Use a registry based to export the Maya shading network to an equivalent UsdShade network.
-selection	-sl	noarg	false	When set, only selected nodes (and their descendants) will be exported
-stripNamespaces	-sn	bool	false	Remove namespaces during export. By default, namespaces are exported to the USD file in the following format: nameSpaceExample_pPlatonic1
-worldspace	-wsp	bool	false	Export all root prim using their full worldspace transform instead of their local transform
-staticSingleSample	-sss	bool	false	Converts animated values with a single time sample to be static instead
-geomSidedness	-gs	string	derived	Determines how geometry sidedness is defined. Valid values are: derived - Value is taken from the shapes doubleSided attribute, single - Export single sided, double - Export double sided
-verbose	-v	noarg	false	Make the command output more verbose
-customLayerData	-cld	string3	none	Set the layers customLayerData metadata. Values are a list of three strings for key, value and data type
-metersPerUnit	-mpu	double	0.0	(Evolving) Exports with the given metersPerUnit. Use with care, as only certain attributes have their dimensions converted. The default value of 0 will continue to use the Maya internal units (cm) and a value of -1 will use the display units. Any other positive value will be taken as an explicit metersPerUnit value to be used. Currently, the following prim types are supported: Meshes Transforms
-exportDistanceUnit	-edu	bool	false	Use the metersPerUnit option specified above for the stage under its metersPerUnit attribute
-upAxis	-upa	string	mayaPrefs	How the up-axis of the exported USD is controlled. "mayaPrefs" follows the current Maya Preferences. "none" does not author up-axis. "y" or "z" author that axis and convert data if the Maya preferences does not match.
-unit	-unt	string	mayaPrefs	How the measuring units of the exported USD is controlled. "mayaPrefs" follows the current Maya Preferences. "none" does not author up-axis. Explicit units (cm, inch, etc) author that and convert data if the Maya preferences does not match.

Note: the -metersPerUnit and -exportDistanceUnit are one way to change the exported units, the -unit is another. We keep both to keep backward compatibility, but the -unit option is the favored way to handle the units.

Frame Samples

The frame samples are computed after the frame stride is taken into account. If any of your frame samples falls outside the open interval (-frameStride, +frameStride), a warning will be issued, but export will proceed normally.

Note: If you have frame samples > 0.0, additional frames may be generated outside your frame range.

Examples:

frameRange	frameStride	frameSample	Time samples in exported USD file
[1, 3]	1.0	-0.1, 0.2	0.9, 1.2, 1.9, 2.2, 2.9, 3.2
[1, 3]	1.0	-0.1, 0.0, 0.2	0.9, 1.0, 1.2, 1.9, 2.0, 2.2, 2.9, 3.0, 3.2
[1, 3]	2.0	-0.1, 0.2	0.9, 1.2, 2.9, 3.2
[1, 3]	0.5	-0.1, 0.2	0.9, 1.2, 1.4, 1.7, 1.9, 2.2, 2.4, 2.7, 2.9, 3.2
[1, 3]	2.0	-3.0, 3.0	-2.0, 0.0, 4.0, 6.0

The last example is quite strange, and a warning will be issued. This is how it will be processed:

• The current time starts at 1.0. We evaluate frame samples, giving us time samples -2.0 and 4.0.
• Then we advance the current time by the stride (2.0), making the new current time 3.0. We evaluate frame samples, giving us time samples 0.0 and 6.0.
• The time samples are sorted before exporting, so they are evaluated in the order -2.0, 0.0, 4.0, 6.0.

Export Behaviors

Model Hierarchy and Kind

MayaUSDExportCommand currently attempts to make each root prim in the exported USD file a valid model, and may author a computed kind on one or more prims to do so. In the future, we plan to support annotating desired kind in the Maya scenegraph, and possibly make further kind/model inference optional. The current behavior is:

• We initially author the kinds on prims based on the -kind flag in MayaUSDExportCommand (see the MayaUSDExportCommand flags above) or the USD_kind attribute on individual Maya nodes (see the "Maya Custom Attributes" table below).

• For each root prim in the scene, we validate the kind if it has been specified. Otherwise, we compute a kind for the root prim:

  • If the root prim is specified to be an assembly (or type derived from assembly), then we check to make sure that Maya has not created any gprims (UsdGeomGprim-derived prim-type) below the root prim. If there are any gprims below the root prim, then MayaUSDExportCommand will halt with an error.
  • If the root prim has no kind, then we will compute a value for the kind to ensure that all root prims have a kind. We determine whether a root prim represents a component (i.e. leaf model) or assembly (i.e. aggregate model of other models, by reference) by determining whether Maya directly created any gprims (UsdGeomGprim-derived prim-type). If Maya has created gprims, model is a component, else it is an assembly.

• Once we have validated or set the kind on each root prim, we go through each root prim's sub-hierarchy to make sure that it is a valid model:

  • If model is a component, but also has references to other models contained (nested) within it, override the kind of the nested references to subcomponent, since component models cannot contain other models according to USD's model-hierarchy rules.
  • Else, if model is an assembly, ensure that all the intermediate prims between the root and the locations at which other assets are referenced in get kind=group so that there is a contiguous hierarchy of models from the root down to the "leaf" model references.

UV Set Names

Currently, for Mesh export (and similarly for NurbsPatch, also), the UV set names will be renamed st, st1, st2,... based on ordering of the primitive. The original name will be preserved in custom data for roundtripping.

Material Scopes

The recommended way of selecting a global scope name for materials is to use the materialsScopeName argument of MayaUSDExportCommand.

If that argument is not specified, we will use "mtl" as a globally defined default. This follows the Guidelines for Structuring USD Assets as defined by the USD Assets WG.

The MAYAUSD_MATERIALS_SCOPE_NAME environment variable can be used to change that default on a global level. The value defined in that env var will take precedence over any value passed in the materialsScopeName argument.

This environment variable was added in part to support legacy user of mayaUSD: in past versions of the plugin, the material scope was named Looks. The change to the new default mtl was done to be aligned with other tools generating USD. As such, the environment variable provides the possibility to use the old Looks name by setting MAYAUSD_MATERIALS_SCOPE_NAME=Looks.

Note that if a user sets both MAYAUSD_MATERIALS_SCOPE_NAME and the Pixar USD_FORCE_DEFAULT_MATERIALS_SCOPE_NAME environment variable, then the Pixar environment variable is used.

Custom Attributes and Tagging for USD

MayaUSDExportCommand has several ways to export user-defined "blind data" (such as custom primvars) and USD-specific data (such as mesh subdivision scheme).

Maya Custom Attributes that Guide USD Export

We reserve the prefix USD_ for attributes that will be used by the USD exporter. You can author most of these attributes in Maya using the Python "adaptor" helper; see the section on "Registered Metadata and Schema Attributes" below.

Maya Custom Attribute Name	Type	Value	Description
All DAG nodes (internal for UsdMaya): Internal to Maya; cannot be set using adaptors.
USD_UserExportedAttributesJson	string	JSON dictionary	Specifies additional arbitrary attributes on the Maya DAG node to be exported as USD attributes. You probably don't want to author this directly (but can if you need to). See "Specifying Arbitrary Attributes for Export" below.
All DAG nodes (USD metadata): These attributes get converted into USD metadata. You can use UsdMaya adaptors to author them. Note that these are only the most common metadata keys; you can export any registered metadata key using UsdMaya adaptors.
USD_hidden	bool	true/false	Equivalent to calling UsdPrim::SetHidden() for the exported prim. Note: in USD, "hidden" is a GUI property intended to be meaningful only to hierarchy browsers, as a complexity management feature indicating whether prims and properties so-tagged should be displayed, similar to how Maya allows you to show/hide shape nodes in the Outliner. Maya's "Hide Selection" GUI operation will cause UsdGeomImageable::CreateVisibilityAttr("invisible") to be authored on export if the -exportVisibility option is specified to MayaUSDExportCommand.
USD_instanceable	bool	true/false	Equivalent to calling UsdPrim::SetInstanceable() with the given value for the exported prim corresponding to the node on which the attribute is authored, overriding the fallback behavior specified via the -exportRefsAsInstanceable export option.
USD_kind	string	e.g. component, assembly, or any other custom kind	Equivalent to calling UsdModelAPI::SetKind() with the given value for the exported prim corresponding to the node on which the attribute is authored. Note that setting the USD kind on root prims may trigger some additional model hierarchy validation. Please see the "Model Hierarchy and kind" section above.
USD_typeName	string	e.g. SkelRoot or any other USD type name	Equivalent to calling UsdPrim::SetTypeName() with the given value for the exported prim corresponding to the node on which the attribute is authored.
All DAG nodes (UsdGeomImageable attributes): These attributes get converted into attributes of the UsdGeomImageable schema. You can use UsdMaya adaptors to author them. Note that these are only the common imageable attributes; you can export any known schema attribute using UsdMaya adaptors.
USD_ATTR_purpose	string	default, render, proxy, guide	Directly corresponds to UsdGeomImageable's purpose attribute for specifying context-sensitive and selectable scenegraph visibility. This attribute will be populated from an imported USD scene wherever it is explicitly authored, and wherever authored on a Maya dag node, will be exported to USD.
Mesh nodes (internal for UsdMaya): Internal to Maya; cannot be set using adaptors.
USD_EmitNormals	bool	true/false	UsdMaya uses this attribute to determine if mesh normals should be emitted; by default, without the tag, UsdMaya will export mesh normals to USD. Note: Currently Maya reads/writes face varying normals. This is only valid when the mesh's subdivision scheme is none (regular poly mesh), and is ignored otherwise.
USD_GeomSubsetInfo	string	JSON	UsdMaya uses this attribute to provide roundtripping information for UsdGeomSubset data.
Mesh nodes (UsdGeomMesh attributes): These attributes get converted into attributes of the UsdGeomMesh schema. You can use UsdMaya adaptors to author them. Note that these are only the common mesh attributes; you can export any known schema attribute using UsdMaya adaptors.
USD_ATTR_faceVaryingLinearInterpolation	string	none, cornersOnly, cornersPlus1, cornersPlus2, boundaries, all	Determines the Face-Varying Interpolation rule. Used for texture mapping/shading purpose. Defaults to cornersPlus1. See the OpenSubdiv documentation for more detail.
USD_ATTR_interpolateBoundary	string	none, edgeAndCorner, edgeOnly	Determines the Boundary Interpolation rule. Valid for Catmull-Clark and Loop subdivision surfaces. Defaults to edgeAndCorner.
USD_ATTR_subdivisionScheme	string	none, bilinear, catmullClark, loop	Determines the Mesh subdivision scheme. Default can be configured using the -defaultMeshScheme export option for meshes without USD_ATTR_subdivisionScheme manually specified; we currently default to catmullClark.

Specifying Arbitrary Attributes for Export

Attributes on a Maya DAG node that are not part of an existing schema or are otherwise unknown to USD can still be tagged for export.

Attributes of a node can be added to Maya attribute USD_UserExportedAttributesJson as a JSON dictionary. During export, this attribute is used to find the names of additional Maya attributes to export as USD attributes, as well as any additional metadata about how the attribute should be exported. Here is example of what the JSON in this attribute might look like after tagging:

{ "myMayaAttributeOne":
{ }, "myMayaAttributeTwo":

{ "usdAttrName": "my:namespace:attributeTwo" }

, "attributeAsPrimvar":

{ "usdAttrType": "primvar" }

, "attributeAsVertexInterpPrimvar":

{ "usdAttrType": "primvar", "interpolation": "vertex" }

, "attributeAsRibAttribute":

{ "usdAttrType": "usdRi" }

"doubleAttributeAsFloatAttribute":

{ "translateMayaDoubleToUsdSinglePrecision": true }

If the attribute metadata contains a value for usdAttrName, the attribute will be given that name in USD. Otherwise, the Maya attribute name will be used, and for regular USD attributes, that name will be prepended with the userProperties: namespace. Note that other types of attributes such as primvars and UsdRi attributes have specific namespacing schemes, so attributes of those types will follow those namespacing conventions. Maya attributes in the JSON will be processed in sorted order. Any USD attribute name collisions will be resolved by using the first attribute visited, and a warning will be issued about subsequent attribute tags for the same USD attribute. The attribute metadata can also contain a value for usdAttrType which can be set to primvar to create the attribute as a UsdGeomPrimvar, or to usdRi to create the attribute using UsdRiStatements::CreateRiAttribute(). Any other value for usdAttrType will result in a regular USD attribute. Attributes to be exported as primvars can also have their interpolation specified by providing a value for the interpolation key in the attribute metadata.

There is not always a direct mapping between Maya-native types and USD/Sdf types, and often it's desirable to intentionally use a single precision type when the extra precision is not needed to reduce size, I/O bandwidth, etc. For example, there is no native Maya attribute type to represent an array of float triples. To get an attribute with a VtVec3fArray type in USD, you can create a vectorArray data-typed attribute in Maya (which stores an array of MVectors, which contain doubles) and set the attribute metadata translateMayaDoubleToUsdSinglePrecision to true so that the data is cast to single precision on export. It will be up-cast back to double precision on re-import.

Export Chasers (Advanced)

Export chasers are plugins that run as part of the export and can implement prim post-processing that executes immediately after prims are written (and/or after animation is written to a prim in time-based exports). Chasers are registered with a particular name and can be passed argument name/value pairs in an invocation of a concrete MayaUSDExportCommand command. There is no "plugin discovery" method here – the developer/user is responsible for making sure the chaser is registered.

For example the pxr plug-in provides one such chaser plugin called AlembicChaser to try to make integrating USD into Alembic-heavy pipelines easier. One of its features is that it can export all Maya attributes whose name matches a particular prefix (e.g. ABC_) as USD attributes by using its attrprefix argument. Here is an example of what that call to mayaUSDExport might look like:

cmds.loadPlugin('pxrUsd')
cmds.mayaUSDExport(
    file=usdFilePath,
    chaser=['alembic'],
    chaserArgs=[
       ('alembic', 'attrprefix', 'ABC_'),
    ])

The export chasers to run are passed by name to the -chaser option, and then an argument to a chaser is passed as a string triple to the -chaserArgs option. Each chaser argument triple should be composed of the name of the chaser to receive the argument, the name of the argument, and the argument's value.

Alembic Chaser Arguments

Argument	Format	Description
attrprefix	mayaPrefix1[=usdPrefix1],mayaPrefix2[=usdPrefix2],...	Exports any Maya custom attribute that begins with mayaPrefix1, mayaPrefix2, ... as a USD attribute. usdPrefix# specifies the substitution for mayaPrefix# when exporting the attribute to USD. The usdPrefix can contain namespaces, denoted by colons after the namespace names. It can also be empty after the equals sign to indicate no prefix. If the entire [=usdPrefix] component (including equals sign) is omitted for some mayaPrefix, the usdPrefix is assumed to be userProperties: by default. This is similar to the userattrprefix argument in Maya's AbcExport command, where the userProperties: namespace is USD's counterpart to the userProperties compound. See "Alembic Chaser attrprefix" below for examples.
primvarprefix	mayaPrefix1[=usdPrefix1],mayaPrefix2[=usdPrefix2],...	Exports any Maya custom attribute that begins with mayaPrefix1, mayaPrefix2, ... as a USD primvar. usdPrefix# specifies the substitution for mayaPrefix# when exporting the attribute to USD. The usdPrefix can contain namespaces, denoted by colons after the namespace names. If the usdPrefix is empty after the equals sign, or if the entire [=usdPrefix] term is omitted completely, then the usdPrefix is assumed to be blank ("") by default. This is similar to the attrprefix argument in Maya's AbcExport command, where the primvars: namespace is USD's counterpart to the arbGeomParams compound. See "Alembic Chaser primvarprefix" below for examples.

Alembic Chaser attrprefix

If attrprefix = ABC_,ABC2_=customPrefix_,ABC3_=,ABC4_=customNamespace:, then the following custom attributes will be exported:

Maya name	USD name
ABC_attrName	userProperties:attrName
ABC2_attrName	customPrefix_attrName
ABC3_attrName	attrName
ABC4_attrName	customNamespace:attrName

Example mayaUSDExport invocation with attrprefix option:

cmds.loadPlugin('pxrUsd')
cmds.mayaUSDExport(
    file=usdFilePath,
    chaser=['alembic'],
    chaserArgs=[
       ('alembic', 'attrprefix', 'ABC_,ABC2_=customPrefix_,ABC3_=,ABC4_=customNamespace:'),
    ])

Alembic Chaser primvarprefix

If primvarprefix = ABC_,ABC2_=customPrefix_,ABC3_=,ABC4_=customNamespace:, then the following custom attributes will be exported:

Maya name	USD name (with primvars: namespace)
ABC_attrName	primvars:attrName
ABC2_attrName	primvars:customPrefix_attrName
ABC3_attrName	primvars:attrName
ABC4_attrName	primvars:customNamespace:attrName

The interpolation of the primvar is based on the _AbcGeomScope attribute corresponding to an attribute (e.g. myCustomAttr_AbcGeomScope for myCustomAttr). Supported interpolations are fvr (face-varying), uni (uniform), vtx (vertex), and con (constant). If there's no sidecar _AbcGeomScope, the primvar gets exported without an authored interpolation; the current fallback interpolation in USD is constant interpolation.

The type of the primvar is automatically deduced from the type of the Maya attribute. (We currently ignore _AbcType hint attributes.)

Example mayaUSDExport invocation with primvarprefix option:

cmds.loadPlugin('pxrUsd')
cmds.mayaUSDExport(
    file=usdFilePath,
    chaser=['alembic'],
    chaserArgs=[
       ('alembic', 'primvarprefix', 'ABC_,ABC2_=customPrefix_,ABC3_=,ABC4_=customNamespace:'),
    ])

Setting Site-Specific Defaults for MayaUSDImportCommand/MayaUSDExportCommand

Suppose that at your site you always want to export with the flags -exportMaterialCollections and -chaser alembic and -chaserArgs ..., even when exporting using the "File > Export All" menu item, where you wouldn't normally be able to set some more advanced options like -chaser that are only available via the specific command, for example the mayaUSDExport command.

You can configure these options as the "site-specific" defaults for your installation of the plug-in, for example the Autodesk Maya USD plugins by creating a plugin and adding some information to its plugInfo.json file (see the USD Plug library documentation for more information).

For example, your plugInfo.json would contain these keys if you wanted the default flags mentioned above:

{
  "Plugins": [
    {
      "Info": {
        "UsdMaya": {
            "UsdExport": {
              "exportMaterialCollections": true,
              "chaser": ["alembic"],
              "chaserArgs": [
                  ["alembic", "primvarprefix", "ABC_,ABC2_=customPrefix_,ABC3_=,ABC4_=customNamespace:"],
                  ["alembic", "attrprefix", "ABC_,ABC2_=customPrefix_,ABC3_=,ABC4_=customNamespace:"]
              ]
          }
        }
      },
      "Name": "MySiteSpecificConfigPlugin",
      "Type": "resource"
    }
  ]
}

This also works for the MayaUSDImportCommand base command, for example in the mayaUSDImport command and the "File > Import" menu item; use the UsdImport key in the plugInfo.json file to configure your site-specific defaults.

mayaUSDListShadingModesCommand

The purpose of this command is to translate between nice-names, internal names and annotations for various elements passed to the other commands.

Command Flags

Long flag	Short flag	Type	Description
-useRegistryOnly	-ur	noarg	Modifier to limit all following options to useRegistry modes only
-export	-ex	noarg	Retrieve the list of export shading mode nice names.
-exportOptions	-eo	string	Retrieve the names necessary to be passed to the shadingMode and convertMaterialsTo flags of the export command.
-exportAnnotation	-ea	string	Retrieve the description of the export shading mode option
-findExportName	-fen	string	Retrieve the nice name of an export shading mode
-findImportName	-fin	string	Retrieve the nice name of an import shading mode
-import	-im	noarg	Retrieve the list of import shading mode nice names.
-importOptions	-io	string	Retrieve the a pair of names that completely define a shading mode, as used by the import shadingMode option
-importAnnotation	-ia	string	Retrieve the description of the import shading mode option

mayaUSDListJobContexts

The purpose of this command is to find the names and annotations for registered import and export job contexts.

Command Flags

Long flag	Short flag	Type	Description
-export	-ex	noarg	Retrieve the list of export job context nice names.
-exportAnnotation	-ea	string	Retrieve the description of the export job context option nice name passed as parameter.
-exportArguments	-eg	string	Retrieve the export arguments affected by the export job context nice name passed as parameter
-import	-im	noarg	Retrieve the list of import job context nice names.
-importAnnotation	-ia	string	Retrieve the description of the import job context option nice name passed as parameter.
-importArguments	-ig	string	Retrieve the import arguments affected by the import job context nice name passed as parameter
-jobContext	-jc	string	Retrieve the job context name associated with a nice name.

mayaUsdGetMaterialsFromRenderers

The purpose of this command is to return the names of USD-compatible materials associated with the currently loaded renderers.
As of this writing, the returned names are largely hard-coded, as is the selection of renderers:

• MaterialX
• USDPreviewSurface
• Arnold (if installed and loaded)

Return Value

The command returns an array of strings in the format Renderer Name/Material Label|MaterialIdentifier, where the MaterialIdentifier is the internal name that may be used to instantiate the given material.

mayaUsdGetMaterialsInStage

The purpose of this command is to get a list of all materials contained in the USD stage of the given object.

Arguments

Pass the path of the USD object to query for materials as an argument.

Return Value

Returns an array of strings containing paths pointing to the materials in the given object's USD stage.

mayaUsdMaterialBindings

The purpose of this command is to determine various material-related attributes of a given USD object. This includes:

• Determining whether an object has a material assigned.
• Determining whether an object is of a type where allowing material assignment would be sensible in a GUI context.
  Technically, USD allows binding of materials to any object type. This function however contains hard-coded filters intended to prevent material assignments in cases where it does not make sense from a usability perspective: For example, the function will return false for objects such as UsdMediaSpatialAudio or UsdPhysicsScene, as it may be reasonably assumed that the user does not intend to assign a material to these object types.

Arguments

Pass the path of the USD object to query for materials as an argument.

Command Flags

Long flag	Short flag	Type	Default	Description
-canAssignMaterialToNodeType	-ca	bool	false	Determines whether the given object is of a type that accepts material assignments in a GUI context.
-hasMaterialBinding	-mb	bool	false	Determines whether the given object is bound to a material.

Return Value

Returns true or false in response to the given query.

EditTargetCommand

The purpose of this command is to set the current edit target.

Command Flags

Long flag	Short flag	Type	Description
-edit	-e	noarg	Set the current edit target, chosen by naming it in the -editTarget flag
-query	-q	noarg	Retrieve the current edit target
-editTarget	-et	string	The name of the target to set with the -edit flag

mayaUsdSchema

The purpose of this command is to query or apply USD schemas to USD prims. It takes as its main arguments a list of UFE paths.

Command Flags

Long flag	Short flag	Type	Description
-appliedSchemas	-app	noarg	Query which schemas the prims have in common
-schema	-sch	string	The schema type name to apply to the prims
-instanceName	-in	string	The instance name for multi-apply schema
-removeSchema	-rem	noarg	Remove the schema instead of applying it
-singleApplicationSchemas	-sas	noarg	Query the list of known single-apply schemas
-multiApplicationSchemas	-mas	noarg	Query the list of known multi-apply schemas

LayerEditorCommand

The purpose of this command is edit layers.

Command Flags

Long flag	Short flag	Type	Description
-edit	-e	noarg	Edit various element of a layer
-clear	-cl	noarg	Erase everything in a layer
-discardEdits	-de	noarg	Discard changes made on a layer
-addAnonymous	-aa	string	Add an anonynous layer at the top of the stack, returns it
-insertSubPath	-is	int string	Insert a sub layer path at a given index
-muteLayer	-mt	bool string	Mute or unmute the named layer
-lockLayer	-lk	int int string	Lock, System-Lock or unlock a layer and its sublayers. Lock Type: 0 = Unlocked, 1 = Locked and 2 = System-Locked. Include Sublayers : 0 = Top Layer Only, 1 : Top and Sublayers
-refreshSystemLock	-rl	string int	Refreshes the lock status of the named layer. 0 = Only top layer, 1 = Include the sublayers
-replaceSubPath	-rp	string string	Replaces a path in the layer stack
-removeSubPath	-rs	int string	Remove a sub layer at a given index

LayerEditorWindowCommand

The purpose of this command is to control the layer editor window.

Command Flags

Long flag	Short flag	Description
-edit	-e	Edit various aspects of the editor window
-query	-q	Retrieve various aspects of the editor window
-addAnonymousSublayer	-aa	Add an anonynous layer at the top of the stack, returns it
-addParentLayer	-ap	Add a parent layer
-loadSubLayers	-lo	Open a dialog to load sub-layers
-removeSubLayer	-rs	Remove sub-layers
-clearLayer	-cl	Erase everything in a layer
-discardEdits	-de	Discard changes made on a layer
-layerHasSubLayers	-ll	Query if the layer has sub-layers
-isAnonymousLayer	-al	Query if the layer is anonymous
-isLayerDirty	-dl	Query if the layer has been modified
-isInvalidLayer	-il	Query if the layer is not found or invalid
-isSubLayer	-su	Query if the layer is a sub-layer
-isIncomingLayer	-in	Query if the layer is incoming (connection)
-layerAppearsMuted	-am	Query if the layer or any parent is muted
-layerIsMuted	-mu	Query if the layer itself is muted
-layerIsReadOnly	-r	Query if the layer or any parent is read only
-muteLayer	-mt	Toggle the muting of a layer
-layerAppearsLocked	-al	Query if the layer's parent is locked
-layerIsLocked	-lo	Query if the layer itself is locked
-layerAppearsSystemLocked	-as	Query if the layer's parent is system-locked
-layerIsSystemLocked	-ls	Query if the layer itself is system-locked
-lockLayer	-lk	Lock or unlock a layer.
-lockLayerAndSubLayers	-la	Lock or unlocks a layer and its sublayers.
-layerNeedsSaving	-ns	Query if the layer is dirty or anonymous
-printLayer	-pl	Print the layer to the script editor output
-proxyShape	-ps	Query the proxyShape path or sets the selected shape by its path. Takes the path as argument
-reload	-rl	Open or show the editor window
-selectionLength	-se	Query the number of items selected
-isSessionLayer	-sl	Query if the layer is a session layer
-selectPrimsWithSpec	-sp	Select the prims with spec in a layer
-saveEdits	-sv	Save the modifications