Constraint-based object modelling

A two-dimensional constraint-based geometric modelling system FLEXI is presented. Constraints are solved by local propagation of Known states. The weakness of local propagation (it cannot solve cyclic constraints) is explained by an example. A biconnected constraint-description graph is used to support local propagation. As a result of constraint solving, an acyclic constraint-description graph is obtained and it can be observed as a parametric description of a geometric object. The acyclic constraint-description graph stores the sequence of applying constraints for the generation of instances. It is shown that the time complexity of the algorithm for generation of an instance is O(n(2)), where n is the number of basic geometrical elements. In the last part of the paper, we demonstrate how geometrical relations among geometrical objects can be established by introduced geometrical constraints. Finally, FLEXI is appraised against criteria for an ideal constraint-based geometric modelling system.