# Constrained Fitting

Both the FitCircle and the FitEllipse tools let you specify fitting constraints. In the case of the circle tool, you can constrain the circle being fit to a specific RadiusConstraint, while the ellipse tool lets you constrain the ellipse being fit to a specific RotationConstraint.

Using constrained fitting can greatly reduce the time required to compute the fit in cases where the constrained degree of freedom is known. Keep in mind that using constrained fitting can reduce the accuracy of the fit in cases where you specify an incorrect value for the constrained degree of freedom.