Linear constraints for the interpretation of line drawings of curved objects

Drawings of curved objects often contain many linear features: straight lines, colinear or coplanar points, parallel lines and vanishing points. These linear features give rise to linear constraints on the 3D position of scene points. The resulting problem can be solved by standard linear programming techniques. An important characteristic of this approach is that instead of making a strong assumption, such as all surfaces are planar, only a very weak assumption, which disallows coincidences and highly improbable objects, needs to be made to be able to deduce planarity. The linear constraints, combined with junction-labelling constraints, are a powerful means of discriminating between possible and impossible line drawings. They provide an important tool for the machine reconstruction of a 3D scene from a human-entered line drawing.  2000 Elsevier Science B.V. All rights reserved.