Abstract: In parametric CAD graphic design, it is a common operation to modify the parameters of graph objects to regenerate graphics. Users usually need to repeatedly enter parameter values in the geometric constraint system to get a satisfactory solution. In the process of changing the value of parameters, the allowable parameter values are not known to the user beforehand and there is no guide information, so users have to input the parameter values in a trial-and-error way. This paper introduces structural constraints to the field of interval parameters and proposes an algebraic algorithm for determining the valid ranges of parameter values. The complexity of the algorithm is O(n2).

Key words: computer aided design, parametric CAD, parameter ranges, geometric constraints, position constraints, structural constraints