Variable-radius circles are common constructs in planar constraint solving and are usually not handled fully by algebraic constraint solvers. We give a complete treatment of variable-radius circles when such a
circle must be determined simultaneously with placing two groups of geometric entities. The problem arises for instance in solvers using triangle decomposition to reduce the complexity of the constraint
Ching-Shoei, C., Joan-Arinyo, R. "Revisiting variable radius circles in constructive geometric constraint solving". 2002.