UNDERSTANDING OBJECT MOTION

Many types of common objects, such as tools and vehicles, usually move in simple ways when they are wielded or driven: the natural axes of t he object tend to remain aligned with the local trihedron defined by t he object's trajectory. Based on this observation we use a model calle d Frenet-Serret motion which corresponds to the motion of a moving tri hedron along a space curve. Knowing how the Frenet-Serret frame is cha nging relative to the observer gives us essential information for unde rstanding the object's motion. This is illustrated here for four examp les, involving tools (a wrench and a saw) and vehicles (an acceleratin g van, a turning taxi). (C) 1998 Elsevier Science B.V. All rights rese rved.