IK Basics

Inverse Kinematics Basics

The Inverse Kinematics (IK) solver in MotionMuse is a state-of-art numerical solver capable of handling hundreds of joints and bones simultaneously over single or multiple characters. As a Full Body IK solver our IK gives the user full control of multiple IK chains simultaneously, providing precise control for easy character posing. This complexity, however, is completely hidden form the user. For the user our IK is one of the easiest IK to learn and use.

Our IK uses participation for IK chain selection, all participating joints and bones will appear Purple in the viewport. Simply change the participation of the Joints you want to affect and move the Joint, and the IK chain will be set using IK. A simple example can be seen in the following figure.

Each joint has its own participation value, allowing the user to customize the IK chain on the fly. The user can use either translate gizmo, rotate gizmo or press and hold to set the Joint location using IK. If the user sets an unreachable goal, the chain will get fully stretched and a green line will indicate the Joint which IK trying to set, as shown in the following figure.

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Keeping Translation, Rotation Intact

The user can move the Joint using the gizmos as shown above. When using the Translate gizmo the rotation of the Joint is free to move and similarly when using the Rotate gizmo the translation of the Joint is free to move. To keep these fixed the user can hold down the “CapsLock” key to make sure that rotation does not change when using the Translate gizmo and viceversa as shown:

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Joint Types

There are two types of Joints in MotionMuse (Rotation Only and Rotation and Translation). The Rotation only Joints have 3 rotational degrees of freedom (DOF) while the Rotation and Translation Joints have 6 DOF (3 rotational and 3 translational). The type of Joint affects how it will be acted upon by the IK. If the Joint is RotOnly then it will only rotate while a 6-DOF joint can also be translated using IK. It is recommended that RotOnly Joints be used with IK along with the root Joint set as a 6-DOF Joint. If all joints are set to 6-DOF Joints then the IK may modify the skeleton which is not recommended. Following is an example showcasing the difference between using IK for 3-DOF vs 6-DOF Joints.

                                                      Rotation Only (3 DOF) Joints                                          Rotation And Translation (6 DOF) Joints

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Copy and Pasting IK Chains

IK chains can be copied and pasted. Copying (Crontrol+C) a Joint will copy its participating joints and selecting and pasting(Control+V) on another joint will paste the copied chain to the new selected Joint’s chain. This is useful to quickly pose one part of the character’s body to match another.