Catalogue of Artificial Intelligence Techniques
Author(s): H.W. Hughes
At the highest level a hierarchical model consists of a number of complex parts positioned within some global coordinate reference frame. Descending the hierarchy, each part is decomposed into more simple parts each with its own local coordinate frame. At each level the coordinate frame transformation between part and subpart is specified. By allowing degrees of freedom in the transformation it is possible to represent flexible joints between parts. Finally, at the lowest level of the hierarchy, the parts are decomposed into primitives (the basic building blocks) usually either volumes or surfaces (e.g., Generalised Cylinders). An example of this would be the modelling of a human hand. At the highest level would be the complete model of the hand. This would decompose into the palm, fingers and thumb. A finger would decompose further into the primitives representing them.
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