# Inverse Kinematics

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Inverse Kinematics or 'IK' as it is called is a method of animating items where the computer calculates the bending of a joint based on the position of a goal object. In this video, Rich covers modo's planar IK options, how to set up a proper chain and explains all the various options, as well as any gotchas when working with IK.

Users can jump ahead to a specific section by using the Chapter selection widget on the right side of the player or by directly clicking any of the Chapter Title links below.

Tab | Time | Chapter | Description
1 | 01:35 | What is IK | Definition of Inverse Kinematics in modo.
2 | 02:15 | How to Setup IK | Walk through of the steps to set up a proper IK chain.
3 | 08:10 | Orient & Blend | Explanation of the Orient and Blend options of the IK constraint.
4 | 11:35 | Add IK Foot | How to properly add a foot to the end of an IK chain.
5 | 15:10 | IK Goal | Adding of a goal to the IK chain for easy manipulation.
6 | 20:54 | FK/IK Blending | Option to blend between Forward and Inverse Kinematics.
7 | 26:33 | Angle Output | Explanation of the Angle Output option.
| 28:25 | Total Video Time |

Frequently Asked Questions--

Q.) Inverse Kinematics is the "Inverse" of what?

> A.) Forward Kinematics or simple parenting. Check out the Parenting and Hierarchies section for more info.

Q.) "Planar IK" what does that mean?

> A.) The smallest number of points that can be used to define a "plane" is 3. If you watch modo's IK work you will notice that the top middle and bottom always work in a "Plane". This limits the kind of motions it can do, but also makes things much faster. Another term for this kind of IK is "Numerical", meaning that you can derive the result with a strait forward math equation. Other types of IK (over 3 points, riding on splines, etc...) are often called "Iterative". This means the IK solver has to keep processing the IK over and over getting a little closer to the target result each time.

Q.) He parented the locators together and little bars drew in between them, what is that?

> A.) Those are "Links". You find these options in the display tab for the locators in question. Check out the Locator Display section for more info.

Q.) Up Vectors for IK, I thought they were used for Constraints?

> A.) It's the same concept for both IK and Constraints... define where "Up" is. Check out the Constraints section for more info.

Q.) He keeps mentioning a "Matrix4D" channel but I only see a "Matrix4" what's the difference?

> A.) There is none. Matrix4 and Martix4D are just terms for a 4x4 matrix. So just ignore him when he adds that silly "D" at the end. If you want to learn a bit more about what a matrix is, check out the Channels section.

Q.) He's constantly renaming items, modifiers, channels... everything, is that really that big a deal?

> A.) YES. Rig organization is a big deal... the more complexity you add, the more important it is to have the internal parts labeled in a way that makes it easy to find what is doing what. Rigging is similar to programming... and every program has bugs, and so will your rigs. Making things as easy to adjust after the fact as you can will save you a tremendous amount of time later on when you are trouble shooting your rig.

Resources--

Links to the modo in-line help system
Docs: Inverse Kinematics
Docs: Constraints
Docs: Dynamic Parenting
Docs: Schematic

Links to other pages in this training
Training: Parenting and Hierarchies
Training: Assemblies and Rigging UI
Training: Locator Mesh Display
Training: Align Set Drop Tools
Training: Constraints
Training: Channels
Training: Schematic

Files--

Links to the modo scenes used in the video
(click to open in modo)
File: Inverse_Kinematics.lxo

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