Properties of Local Geometric Constraints

Formal analysis shows that the relationship between 2D line segments which is rotationally and translationally invariant can be expressed using four independent variables (five if scale is included). The formalism leads to a language for defining local geometric constraints and describing their properties. This terminology allows us to establish a criterion for evaluating the quality of a constraint set. Finally, a 2D constraint set is described that is deemed useful in light of the criterion proposed.