Schemata for interrogating solid boundaries

Abstract

Data structures used by geometric modellers to construct and modify geometric objects are usually different than those needed by application programs to interrogate the geometry. For example, rendering programs typically use oriented polygons, not the combinatorial boundary information maintained by polyhedral geometric modellers. We describe a mechanism for constructing application views, or schemata, of geometric objects described by a large class of boundary representations. These views are constructed by interposing a layer of software between a geometric modeller and an application program. We call this software layer a schema library. We illustrate the utility of schemata and their libraries by discussing an implemented schema library used by a geometric editor whose underlying geometric modeller manipulates cell-complexes, i.e., polyhedral subdivisions of three-space.