Introduction
Most animals have the ability to sense their world three-dimensionally. Using visual, pressure-related, and chemical cues, which are filtered through sophisticated neural circuitry and central processing, animals continually measure the distance to and shape of objects in their environment. If the objects are moving, as in an oncoming predator, or fleeing prey, animals automatically track and predict trajectories, allowing both escape and interception. Of course, all of these complex calculations are processed in real time. When we attempt to emulate these feats of three-dimensional perception with scientific instruments and complex computers, we quickly discover that four-dimensional measurement is extremely difficult.
This chapter is a general survey of the area of three-dimensional sensing. In recent years, three-dimensional sensing has seen much development, and there is every indication that the current proliferation of computer techniques and capabilities will fuel the continued acceleration of this field. The primary goal of this chapter is to review present methods used to measure the three-dimensional patterns of individuals as well as aggregations of animals in the laboratory and the field. Secondarily, I will comment on the future potential of methods under development.
In a very general sense, the requirements for three-dimensional imaging should be examined with respect to the information that one is interested in. However, most applications require measurement in both space and time. For instance, in the area of medical imaging, both static (i.e. anatomical) and dynamic (i.e. physiological) information is necessary to judge individual health. In the case of astronomy, both the position and the trajectory of heavenly bodies are necessary to deduce the dynamic laws by which the solar system evolves.