A Human Body Modelling System for Motion Studies

The need to visualize and interpret human body movement data from experiments and simulations has led to the development of a new, computerized, three-dimensional representation for the human body. Based on a skeleton of joints and segments, the model is manipulated by specifying joint positions with respect to arbitrary frames of reference. The external form is modelled as the union of overlapping spheres which define the surface of each segment. The properties of the segment and sphere model include: an ability to utilize any connected portion of the body in order to examine selected movements without computing movements of undesired parts , a naming mechanism for describing parts within a segment, and a collision detection algorithm for finding contacts or illegal intersections of the body with itself or other objects. One of the most attractive features of this model is the simple hidden surface removal algorithm. Since spheres always project onto a plane as disks, a solid, shaded, realistically-formed raster display of the model can be efficiently generated by a simple overlaying of the disks from the backmost to the frontmost. A three-dimensional animated display on a line-drawing device is based on drawing circles. Examples of the three-dimensional figure as viewed on these different display media are presented. The flexibility of the representation is enhanced by a method for decomposing an object into spheres, given one or more of its cross-sections, so that the data input problem is significantly simplified, should other models be desired. Using data from existing simulation programs, movements of the model have been computed and displayed, yielding very satisfactory results. Various transportation related applications are proposed.