Inverse kinematics

Inverse kinematics

Inverse kinematics is the process of determining the parameters of a jointed flexible object (a kinematic chain) in order to achieve a desired pose. Inverse kinematics are also relevant to game programming and 3D animation, where a common use is making sure game characters connect physically to the world, such as feet landing firmly on top of terrain.

An articulated figure consists of a set of rigid segments connected with joints. Varying angles of the joints yields an indefinite number of configurations. The solution to the forward kinematic animation problem, given these angles, is the pose of the figure. The solution to the more difficult "inverse kinematics problem" is to find the joint angles given the desired configuration of the figure (i.e., end effector). In the general case there is no analytic solution for the inverse kinematics problem. However, inverse kinematics may be solved via nonlinear programming techniques. Certain special kinematic chains—those with a spherical wrist—permit kinematic decoupling. This treats the end effector's orientation and position independently and permits an efficient closed-form solution.

Inverse kinematics is a tool utilized frequently by 3D artists. It is often easier for an artist to express the desired spatial appearance rather than manipulate joint angles directly. For example, inverse kinematics allows an artist to move the hand of a 3D human model to a desired position and orientation and have an algorithm select the proper angles of the wrist, elbow, and shoulder joints.

Other applications of inverse kinematic algorithms include interactive manipulation, animation control and collision avoidance.

See also

*Forward kinematic animation
*Forward kinematics
*Inverse kinematic animation
*Kinemation
*Jacobian
*Joint constraints
*Levenberg-Marquardt algorithm
*Physics engine
*Pseudoinverse
*Ragdoll physics
*Arm solution

External links

* [http://www.virtualitoy.com/Fashion/DressUpDolls/Item/?Item=DressUpDoll_myGuitar_Axe Advanced Application of Inverse Kinematics using ActionScript]
* [http://freespace.virgin.net/hugo.elias/models/m_ik2.htm Inverse Kinematics algorithms]
* [http://www.learnaboutrobots.com/inverseKinematics.htm Robot Inverse Kinematics]
* [http://entertainment.howstuffworks.com/question538.htm HowStuffWorks.com article "How do the characters in video games move so fluidly?"] with an explanation of inverse kinematics
* [http://www.euclideanspace.com/physics/kinematics/joints/index.htm 3D Theory Kinematics]
* [http://cnx.org/content/m11613/latest/ Protein Inverse Kinematics]
* [http://diegopark.googlepages.com/computergraphics Simple Inverse Kinematics example with source code using Jacobian]
* [http://billbaxter.com/courses/290/html/index.htm Detailed description of Jacobian and CCD solutions for inverse kinematics]


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