When this option is off, you can move the start joint away from the curve. The start joint is no longer constrained to the curve. Maya ignores the Offset attribute, and no offset manipulator exists at the start joint.
When this option is on, a parent transform node above the start joint in the scene hierarchy is created with the spline IK handle. You can avoid unexpected start joint flipping by moving and rotating this transform node rather than the start joint. See for details.You can turn on this option only when Root on Curve is off.
If the start joint of the spline IK handle has a parent, this setting makes the spline IK NURBS curve a child of that parent. Therefore, the curve and joint chain moves with the transformations of the parent.
If you create a handle that starts at a joint in the chain lower than the root joint of your skeleton, turn this option on to ensure that the joint chain moves with the transformations of its parent joint.
If Auto Create Curve is on and Auto Simplify Curve is on, creating the handle automatically creates a simplified curve that has a shape similar to the joint chain. The higher the Number of Spans, the closer the curve matches the joint chain. The curve has a curve degree of 3 (cubic).
If the spline IK joint chain is part of an existing skeleton, you should turn Auto Create Curve on. If you are using a curve as a path for sliding the joint chain, you should turn Auto Create Curve off.
When this option is on, Maya automatically creates a NURBS curve with the specified Number of Spans. The number of spans corresponds to the number of CVs in the curve. The curve has a curve degree of 3 (cubic).
If you create a curve with few CVs, your control of the curve’s shape and skeleton’s movement will be less precise, but you will be able to easily manipulate the curve and its joint chain. With fewer CVs, you will spend less time selecting and dragging CVs, and you are more likely to have a smooth curve.
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