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Intuitive semantically constrained interaction in feature-based parametric design

: Stork, A.; Brunetti, G.; Vieira, A.S.

Ruland, D. ; Gesellschaft für Informatik -GI-, Bonn; Deutsches Forschungszentrum für Künstliche Intelligenz:
Verteilte und intelligente CAD-Systeme. Tagungsband
Kaiserlautern, 1996 (Informatik XPress 8)
CAD <1996, Kaiserslautern>
Fraunhofer IGD ()
constrained 3D interaction; direct manipulation; feature based parametric design; visual feedback

Feature-based parametric design (FbPD) is currently one of the most discussed advanced modelling techniques in CAD. Its basic idea is to enable the user to model in a higher level of abstraction, combining funcionality and design intent with geometry. Using FbPD the user works in his own terms, such as create a screw hole, make a slot, etc., instead of breaking each operation down to the geometric and mathematic level. From the semantics of a feature, the applicable set of operations is constrained, e.g. it is not valid to make a hole bigger than its surrounding solid. To check whether a given feature inter-relationship fulfils all defined constraints, constraint solving techniques are used. Constraints can either be defined intrisically by a feature or extrisically by the user, e.g. the forces applied to a feature o the system, we face the questions. In an interactive, direct manipulative feature-based modelling system, we face the questions: When to process the constraints? Should th e user be allowed to create invalid models? Will such situations be rejected by the constraint solver afterwards? How can we insure valid models, decrease the number of calls to the constraint solver and still being direct manipulative? This paper presents an approach that handles the constraints in the user interface level by solving them in advance of an interaction, determining the degrees of freedom and parameterizing the appropriate interaction technique. These interaction techniques are realized by so-called manipulators, allowing intuitive direct manipulation. Limiting the supported manipulation possibilities, the user can only carry out valid modifications with respect to the constraints and no constraint solving is needed during the interaction.