Spline attributes

Primitive Type: Controls the kind of primitive that the Description generates.

Splines: Spline primitives are curves made up of two or more segments. Use Splines for fur, simple stiff shapes, and complex ribbon shapes like long or curly hair.
Sphere: Sphere primitives define a sphere with controllable length, width, and depth.
Cards: Card primitives define a NURBS patch that is attached to the patch at the center.
Archive: Archive primitive use the generic attributes to instance Alembic-based geometry that is specified by an XGen archive (.xarc) file.

See Custom archive primitives.

Control using: Sets whether primitive Attributes or Guides control the grooming of the Description. (Groomable Splines are controlled by Attributes and image maps created by the grooming tools.

Guides: When selected, guides control the placement and shape of the primitives. Guides use an interpolation algorithm to calculate the placement and shape of associated primitives. See Guides.
Attributes: When selected, the groom is driven procedurally using attributes and expressions. No guides or guide interpolation is used to place or shape the resulting primitives. See Control primitives using attributes and expressions.

Attr CV Count: Sets the number of Control Vertices (CVs) that each Spline has under attribute control. By default, there is only a start, middle, and end point, which allow a single bend. You can increase this number to get additional bend parameters to control.
Modifier CV Count: If you apply Modifiers to this description, the splines may need more flexibility to bend. This sets the number of Control Vertices (CVs) that each spline has available for the Modifier Stack.
Uniform CVs: Reparameterize the splines so that their CVs are uniformly spaced along the length. You can turn this off for long hair, but otherwise leave it on.
Length: Controls the length along the curve.

When Control using is set to Attribute, this value sets the primitive length. When Control using is set to Guides, Length scales primitive length based on the guide length.
Width: Controls the Spline width as the cross sectional width of the curve.

When Control using is set to Attribute, this value sets the primitive width. When Control using is set to Guides, Width scales primitive width based on the guide width.
Taper: Controls the width at the tip of each spline compared to its base. Positive values make the tip narrower than the base, and negative values make the tip wider than the base.
Taper Start: Controls where the spline width starts to taper. Taper Start ranges from 0.0 (the base) to 1.0 (the tip).
Tilt U: Tilts primitives away from the surface normal. 0 is no tilt, and 1.0 is a 90-degree tilt.
Tilt V: Tilts primitives away from the surface normal, but at right angles to Tilt U.
Tilt N: Magnifies how much the primitive tilts away from the surface normal by Tilt U and Tilt V. If Tilt U and Tilt V are 0, then Tilt N has no effect.
Around N: Rotates the primitive orientation around the surface normal. This vector is not affected by Bump, Tilt V and Tilt V.

This has no apparent effect until the splines are bent or tilted with Tilt U Tilt V, Bend U, or Bend V.
Bend Param[0]: Controls where along the spline bending occurs. Ranges from 0.0 (the base of the spline) to 1.0 (the tip). A set of bend controls are created for each curve CV aside from the base and tip.
Bend U[0]: Controls how much the spline is bent at the corresponding CV. 0 is no bend, and 1.0 is a 90-degree bend.
Bend V[0]: Controls how much the spline is bent at right angles to the corresponding CV. 0 is no bend, and 1.0 is a 90-degree bend.
Options

Display Width: Turn on to display the spline width and taper in the Maya scene view. The spline width displays as a poly-strip.
Face Camera: Turn on to make each primitive rotate so its flat side faces towards the camera as much as possible. This has no apparent effect if Display Width is turned off.

For splines, this sets the width cross section to always be perpendicular to the camera. Face Camera does not affect the pose of the spline, just the cross section. When not set, the width cross section will be set such that it is orthogonal to each joint bend direction.
Tube Shade: Displays the previewed splines so that they appear tubular, rather than flat. Tube Shade only works in Viewport 2.0 and has no effect on the final render.

Guide Tools

Rebuild: Rebuilds the guides with the set number of spans without changing the guide shape. Click Guide to open the Rebuild Guide window to specify the number of spans with which to rebuild the guides.
Normalize: Rebuilds the guides to ensure evenly spaced spans.

Set Length: Rebuilds the guides based on the value you set in the Set Guide Length window.
Tube Groom: Opens the Tube Based Grooming window, which lets you use a Maya polygon cylinder object to create a spline clumping effect.

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