An orientation method for central projection programs

Abstract

A centrally projected image is based on an object, a viewpoint and a viewer orientation. The programs reported to date which calculate centrally projected images require all of these as input. Instructions for the programs usually suggest that the hypothetical observer face toward the center of the object. There are two major problems with this: (1) there may be no clear way of defining the “center”, and (2) an orientation chosen in this manner may result in parts of the object lying behind or to the side of the observer and hence being invisible or severely distorted under the projection. This paper describes an algorithm for calculating a viewing direction which will render visible the entire object whenever this is possible, and will furthermore minimize distortion in the projected image.