Microsoft KB Archive/171757

= Microsoft Knowledge Base =

INFO: Differences Between 2D and 3D Chains
Last reviewed: July 31, 1997

Article ID: Q171757

The information in this article applies to:


 * Softimage 3D for IRIX, versions 3.51, 3.7
 * Softimage 3D for Windows NT, versions 3.51, 3.7

SUMMARY
Consider the following when deciding whether to use 2D or 3D chains:


 * The first joint of a 2D chain is always a ball joint and when used with inverse kinematics, the joints following the root rotate only on the z-axis; whereas with a 3D chain, every joint is a ball joint and can be rotated on any axis.
 * All three local axis are used if keyframing is used on the orientation of the joints of a 2D chain, whereas when using keyframing, dynamic simulation, or inverse kinematics with 3D chains, the joints are rotated on all three local axis and not constrained by the other joints' orientations.
 * 2D inverse kinematic chains calculate the intermediate orientation of joints on a plane (i.e.: a door hinge), whereas 3D inverse kinematic chains calculate the intermediate orientation of joints in 3d space, like a ball bearing.
 * If your object needs to bend on only one plane (such as legs and arms), you can successfully achieve this by using 2D chains. If you are animating an object that needs to twist on any plane (such as a spiral), then you must use 3D chains; if you used a 2D chain, the result would be a planar spiral.

NOTE: 3D chains are marginally slower than 2D chains because of the extra computations required to calculate the position of each joint in 3d space, compared to the one calculation (the relative z-axis computation relative to one plane) for joints in a 2D chain.