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The Study of Animation - Hierarchical Modelling for Animation Print E-mail
Wednesday, 05 September 2012 00:18


design blog - Hierarchical Modelling for Animation article

Today, we will talk a little bit about the technology, and more precisely about the technology of animation. Everybody of you probably have watched great animation movies such Avatar, Ice of Age or similar, but what do you know about the technology that has been involved to create animating Jake Sully when being an avatar, Manny or Sid? This article begins the "Trilogy" called The Study of Animation and it is a part no. 1 out of 3 which will be written in next 2-3 weeks time. Today we will focus on Hierarchical Modelling for Animation, so please pop in more often for updates regarding the animation technology.


Animation techniques applied to a virtual character have a large number of applications being done so far. However, the animation technology is a pretty young subject and there is still a need for the application that combines different techniques to present full-functional animation system. The study introduces specific research areas:

-    Hierarchical Modelling for Animation (Part 1)
-    Mesh-on-Skeleton Animation (Part 2)
-    Motion Capture Technology (Part 3)




Hierarchical Modelling for Animation


In the Computer Animation the animation of simple objects, such as box or cube, is done by changing the parameters of given object in the transformation matrix. Regarding to an animator M. O’Rourke , interpolation of the transformation values over a sequence of computer-generated frames can bring to life basic animation of the object.


However, in the interest of this project is to discuss the nature of animating more complex model, such like avatar, which requires more complicated methods of animation in 3D environment. In fact, to animate the model of an avatar, we need to know avatar’s physique and shape to understand his ability of moving. In Computer Graphics, there is a way that lets the user know about it, called an articulated model.



articulated model in 3d modelling and 3d animation


A debate about strong relationship between articulated model and its value for motion tracking confirms this idea. Briefly, an articulated model is a collection of parts (for example limbs, head, and body) which need to be organized into a hierarchical structure, known as tree structure. The position of individual part is determined by the position of part higher in the entire hierarchy.


design blog - Forward Kinematics and Inverse Kinematics articleBy doing this the user gets relatively more control over the transformations applied separately to every each element of the model. In computer graphics it plays a huge role in terms of using specialized graphics tools and applications for pre-producing 3D models and controlling their structure at this stage.


Once this is achieved and if the model is structured properly the animation can be applied beginning by translating related elements of the body to produce required motion in the 3-dimensional space. Animator O’Rourke states that in order to clearly animate the model the difference of two techniques, called Forward Kinematics and Inverse Kinematics, needs to be studied - both can make totally different effects.


Forward Kinematics calculates the movements of particular part from the position and orientation of the object, in the normal way, downward the tree structure. In case of using Inverse Kinematics the position and orientation of each part of the articulated model is determined by desired position of certain parts of the model, movement is calculated upward the tree structure. Nowadays, both of these methods are widely used to make the animation, because of their simplicity, and both could be used in creating a real-time application.



In a summary, animation is a pretty "tricky" matter which, as you can see, involves a lot of studies, both of maths and physics. However, we will skip the hard parts of heavy science and focus about the theory only, just to make things easier and to show you how animation works. Do not forget there are still 2 parts continuing the matter of animation technology, so see you next time.


You may also be interested in 3D TV article.






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