3D Toolkit: Rigging Introduction

Rigging Introduction
Rigging is the process of creating an underlying skeleton that aligns to the geometry of a character and allow for movement and animation. Rigs are comprised of two components: Joints, which act as individual points of rotation such as a knee, elbow, shoulder or knuckle), and Bones, which connect Joints together. 

Rigging is a precise process in which Joints must be aligned on a single axis. As such, when I have created a practice skeleton rig, I have aligned my view to a side orthographic view: this shows a physical grid in which the Joints can be precisely placed atop. To get a Joint placement to snap to this grid, I hold the 'X' key when using the movement tool. 

The Create Joint tool allows for Joints to be placed in the project space. After placing one Joint, if another is immediately placed, the two Joints will be linked with a Bone. Bones are represented in Maya as a pyramid-like shape, which is at its widest at the point of origin and tapers towards the ending Joint. Rigging works through orders of hierarchy: one joint is connected to another, with the point of origin moving Joints that are subsidiary to it. As shown below, the three joints that comprise the lower leg (the ankle, foot and toe) are subsidiary to the knee: selecting the knee also selects these Joints.

The practice rig I created was that of a leg, beginning with the joint that connects the thigh to the pelvis and following through the leg to terminate in the toes. This single leg must then be connected to another Joint, representing where the pelvis connects to the spine. 
When creating this Joint, I first moved the leg into position. This broke the chain of creation that would connect one Joint to another: when I placed the hip Joint, it was unconnected to the leg. To make it connected, I had to parent the hip joint to the leg. To do this, I selected the leg, then shift+selected the hip and pressed 'P'. This connected the two joints with a bone that originated from the hip joint and terminated at the leg. To create the other leg, I then mirrored the selection of the leg on the X axis. This created the joints and bones of the right leg, which were connected to the pelvis.

IK handles can be used to create connections between joints, showing where joints and bones rotate around one another, allowing for movement in which bone lengths remain constant whilst rotating around a joint. This can create the extending / folding motion of an elbow or knee. In this example, I wanted to create the connection between the ankle and the hip: with the knee displaced forward, when this connection between the ankle and hip is lowered, the knee is pushed forward and the bones fold up beside it. This creates an arching motion, raising the foot and bending the knee.

To do so, I changed the IK handle settings to be Rotation-Based and 'Sticky'. I then clicked on the hip and ankle joints, creating the connection between them. When creating the connections between the ankle, foot and toe joints, 'single chain solver' IK handles can be used. These are used for bone motions that are more simplistic than those seen in folding joints.

When creating IK handles for specific motions and functions, multiple Groups set up in a hierarchy of motion can be used. This is primarily used to add different pivot points to IK handles, allowing for bones to be moved in different orientations whilst keeping the outliner organised and concise. This is incredibly important, as rigs can contain many bones and many groups within them: ensuring that all are adequately sectioned and organised is crucial to maintaining an understanding of how specific motions can be made with the groups and IK handles available.

In this practice, I created a series of groups around the leg, using CTRL+G to creat a group off a selection and accurately moving the pivot using the D+V keys to were appropriate. I then renamed the group to ensure order in the hierarchy.