L.Cooper, "Physically based modelling of human limbs", PhD, 1998. (Supervisor: Dr Steve Maddock). [pdf]
(The electronic copy of the PhD is has been compiled from some postscript files that are slightly corrupted. The resolution of the pdf file is not great, but is readable. Also, the files are not the final version of the thesis - some corrections were made.)
PhD abstract: Existing research into modelling the human body has typically created either oversimplified models for representing characters in computer animation, or accurate models of specific tissue regions for medical/biomechanical applications. The work presented in this thesis attempts to bridge the gap between these two fields by creating a moderately accurate physically based model of an entire limb, combining a range of new and existing techniques.
In order to consider the effectiveness of existing approaches, and make informed decisions during the design of the model, a study is made of the relevant biomechanical issues. This includes consideration of anatomy, the material properties of soft tissue, and the deformation effects that occur at the skin surface. A complete, albeit simplified, physical based model of a leg is presented, which features a skeleton, two musculotendon structures (to flex and extend the knee), and a layer of flesh. The model is complete in that it operates in the same way as real limbs: muscle activation exerts forces on the skeleton via tendons, these are combined with other forces (for example due to gravity), and the resulting motion of the skeleton leads to deformation of the soft tissue regions, including the muscles and tendons themselves. Soft tissue behaviour is represented using an enhanced Mass-Spring-Damper approach which models the material properties of real soft tissue including its uni-axial stress-strain characteristics and limited compressibility.
Results are presented from a number of tests, which specifically recreate situations in which many existing models behave incorrectly. The leg model is shown to behave in a physically and visually realistic way, exhibiting skin deformation effects which include creasing around the knee joint when bent, bulging of contracted muscles, wobbling of flesh, and deformation due to contact with external objects. A simple verification study is presented based on video footage of a real leg.
