Making Hierarchical Models for Life Forms   Life Forms uses jointed models to create animations. The primary characteristic of a jointed model is that the relationship between joints is specified in a hierarchy. The geometry of each joint is also specified, along with its rotations, and pivot point. Introduction to Hierarchical Models Hierarchy of the default human skeleton Guidelines for creating models to be animated in Life Forms Introduction to Hierarchical Models. A hierarchy is based on the parent-child relationship. Each joint is called a node in the hierarchy. The child node is affected by everything done to the parent node: rotations, translations, scaling, etc. In such a hierarchy, there is always a root node, which is the ultimate parent of all other nodes in the hierarchy. Each parent can have zero or more children. The child nodes of a common parent are called siblings, the nodes below a given node are called descendants, and the nodes above a given node are called ancestors. The pivot point of the joint is the center of rotation for the joint. For instance, in the upper arm, the pivot point would be at the shoulder. For a joint that defines the chest, the pivot point would be near the lower back. For the foot, it would be near the ankle. If the nodes of the skeleton correspond to the parts of the body, then the pivot points correspond to the joints of the body. When a node is rotated, it rotates around its defined pivot point, and all descendants are affected by the rotation. Thus, when the upper arm moves, it pivots the shoulder, and because the lower arm is a child of the upper arm, the lower arm, hand and fingers will rotate as well. In most modelers, scaling and translations applied to a parent node will also affect descendant nodes. Note: In Life Forms, the root node of the human skeleton is the pelvis. The pivot point of is the center of the pelvis. When the pelvis is rotated the entire body rotates, and when the pelvis is moved (translated), the entire body moves with it.   Heirarchy of the Life Forms default human skeleton     Guidelines for creating models to be animated in Life Forms Hierarchy Body parts must be linked together. In most modeling programs, there is some sort of "link to" where you specify the parent-child relationship between objects. Pivot Points The pivot points must be set. In some modeling software, the pivot point can be set using a "pivot tool", but in others, the pivot point of a joint is always at the origin or center point for the joint. Scaling The models must be scaled correctly. The default units in Life Forms are either Meters or Feet. Life Forms attempts to convert the source file's units to Meters or Feet. Make sure you are using the correct units. If you import a model and it is either very large or very small, adjust the scaling in the modeler to make sure you can export it correctly later. If you adjust the scaling in Life Forms, then any animation you make will be in the new scale Default Position Create the body parts so their default position (all angles equal 0) is the same as the default human figure. This is very important if you are going to copy animations made with the default human figure to this new model. The default position is shown in the diagram above: feet together, pointing forward, hands at the sides, thumbs pointing forward. If the figure is not in the default position, it is still possible to use it in Life Forms. Import the figure, orient the limbs in the proper default position, and then choose Set default shape from the Edit menu to set the figure's new default shape. Proportions If you are going to copy animations made with the default human figure to a new model, then the more similar the proportions of the model to the default figure the better it will map. Joint Names If you name the joints of the new model the same as the joints in the default human figure, Life Forms can often guess the proper mappings when copying animation data to the new model. Joint Map Editor More information on mapping animation data from other models can be found in the chapter of the Life Forms manual on the Joint Map Editor. Complexity The Life Forms default human model has 24 joints in the spine, grouped into the upper back, lower back and neck. In Life Forms, these are manipulated as a group by distributing the angle between the joints. When modeling your own human model we recommend that you use one back joint, three back joints, or 24 back joints. If you use one back joint, you should map the upper back, lower back and next to the single joint of the back. If you use three back joints, map one to each of the corresponding groups in life forms. If you use 24 back joints, you should name them the same as Life Forms so that they can automatically map to the right group. We suggest that you try the model out in Life Forms frequently while you are building it to check that it works they way you want it to.     home | company | products | downloads | gallery | support | sales Copyright ©1990-1998 Credo Interactive Inc. info@credo-interactive.com | webmaster@credo-interactive.com