2009

Table Of Contents
Lesson 5: Inverse kinematics
Introduction
Inverse Kinematics (IK) allows you to efficiently pose your models and
characters for animation. You pose the skeleton by positioning IK handles,
usually located at the end of an IK joint chain (for example at the hand). The
rotations for the other joints are calculated automatically by an IK solver. An
IK solver calculates the rotations of each joint back up the hierarchy of the
joint chain based on the position of the IK handle. See
Creating a skeleton
hierarchy
on page 267 for more information on skeletons and joints.
By contrast, Forward Kinematics (FK) requires you to rotate each joint in turn
until you have the desired pose for a keyframe. This can be a tedious process
when posing a complex skeleton. When using Inverse Kinematics, its faster
to pose a character because the joint rotations further up the hierarchy are
calculated automatically based on the placement of the IK Handle. Using both
FK and IK techniques on the same skeleton is called FK/IK blending.
IK is obviously useful for posing animated characters that have a skeleton
(two-legged, four-legged etc.) and has others applications, such as posing
skeletons within mechanical-like models.
The goal of this lesson is to animate a mechanical arm so that it extends into
a position over a cargo box, picks up and moves the cargo box to another
location, and then sets it down.
262 | Chapter 6 Animation