USD prim types in the Outliner

To differentiate between various prim types, USD data in Maya features a unique set of prim icons and composition arc badges that are viewable from the Outliner.

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Prim Type Icon Index

Prim type icons in the Outliner are based on an inheritance schema, which allows the descendants of a prim to gain a parent prim's icon unless it has a unique icon created for itself.

Icon	Prim Type	Description
	Class	A special type of prim that acts as a template, storing reusable properties and values that can be inherited by other prims in a scene.
	def	A def is a type-less prim type. Since defs are empty and contain no information, they are used for defining references. A def can easily take on the prim type of the referenced prim, making it the ideal prim type for this scenario.
	Scope	A scope is a container that cannot be transformed. It is the simplest prim type and is useful for creating a hierarchical structure. For example, materials are typically held within a scope, because they do not need to be transformed.
	Xform	An Xform prim defines spatial transformations that can be used to translate, rotate and scale its child prims.
	Capsule	A prim shaped in the form of a capsule; a cylinder capped by two half spheres, centered at the origin, whose spine is along the specified axis.
	Cone	A prim shaped in the form of a cone; centered at the origin, whose spine is along the specified axis, with the apex of the cone pointing in the direction of the positive axis.
	Cube	A rectilinear prim shaped in the form of a cube, centered at the origin.
	Cylinder	A prim shaped in the form of a cylinder, centered at the origin, whose spine is along the specified axis.
	Plane	A prim that defines a flat 2D space.
	Sphere	A prim shaped in the form of a sphere centered at the origin.
	BasisCurves NurbsCurves	BasisCurves are a batched curve representation, often used to render geometry like hair or grass. NurbsCurves are a spec that supports batching of multiple curves into a single prim, widths, and normals in the schema.
	Mesh	A point-based prim that is defined in terms of points that are connected into edges and faces.
	NurbsPatch	A non-uniform spline surface with natural UV parameters. This enables you to "trim curves" and allow smooth shapes to be carved out of a surface.
	Points	A base class for prims that possess points, such as normals and velocities.
	Volume	A renderable volume prim.
	PointInstancer	A vectorized instancing of multiple, potentially animated, prototypes (object/instances), which can be arbitrary prims/subtrees on a stage. PointInstancer is a "multi instancer", as it allows multiple prototypes to be scattered among its "points".
	SkelRoot Skeleton	A body and topology of a skeleton.
	MayaReference ALMayaReference	A Maya reference and all its metadata.
	Camera	A transformable (XFormable) camera.
	CylinderLight DiskLight DistantLight DomeLight GeometryLight RectLight SphereLight LightFilter LightPortal	Lights can be linked to geometry. Linking controls which geometry a light illuminates, and which geometry casts shadows from the light.
	GeomSubset	Encodes a subset of a piece of geometry. To apply a subset to a prim, a GeomSubset prim must be defined as a child of it.
	NodeGraph	NodeGraph is a container for shading nodes, as well as other node-graphs.
	Material	A Material provides a container into which multiple "render targets" can add data that defines a "shading material" for a renderer.
	Shader	Shaders are the building blocks of shading networks. These objects generally represent a single shading object, whether it exists in the target renderer or not.
	SkelAnimation PackedJointAnimation	The animation of a skeleton.
	BlendShape	A target blend shape, possibly containing in between shapes.
	Backdrop	Provides a 'group-box' for the purpose of node graph organization.
	someOtherType	Generic fallback for usdTyped schemas.

<SystemFolderPath>/maya/2021/prefs/icons

When naming a file, ensure that it abides by the following nomenclature: out_USD_<nodetype>.png. Icons in Maya are supported for high resolution display, therefore you can include higher dpi versions such as out_USD_<nodetype>_150.png and out_USD_<nodetype>_200.png.

Icon Badges

To distinguish prims that have a composition arc and those that have a variant specifically, USD data in the Outliner features icon badges.

If a prim has any of the following composition arcs: inherit, reference, specialize, payload but doesn't have a variant, then it receives the composition arc badge.

Composition Arcs

Composition arcs are the "operators" that enable you to create relations between many layers in USD. Composition occurs when you open a stage, load or unload prims on a stage, or edit layers that contribute to the stage. There are six kinds of arcs: sublayers, inherits, variants, references, payloads, and specializes. In all arc types, stronger layers override weaker layers.

If a prim has a variant composition arc, then it receives the variant badge in addition to the composition arc badge.

Variants

A Variant is a single, named variation of a variant set. Each Variant Set is a package of alternatives that users can switch between non-destructively. A variant set has no limits to what it can store. A single prim can have many variants and variant sets, but only one variant from each variant set can be selected and set for a prim. Variants can be used to swap out a material or change the entire hierarchy of an asset. Use the USD Contextual Menu in the Outliner to switch between variants in a variant set.

Related Concepts: To learn more, see variant, variantSet in the Pixar USD Glossary.