1. A computer-implemented method for designing a CAD modeled object, wherein the method comprises: displaying at least one parametric three-dimensional shape; user-interacting with the screen; defining on a support a stroke corresponding to the user-interacting; computing at least one geometrical characteristic of the stroke, wherein the geometrical characteristic of the stroke includes one or more of a tangent vector of the stroke, a normal vector of the stroke, a first point of the stroke, a last point of the stroke, a center of a bounding box of the stroke, and a position of the stroke; determining at least one parameter of a geometrical CAD operation based on the computed geometrical characteristic, the geometrical CAD operation having inputs comprising one or more displayed parametric three-dimensional shapes, the parameter determining how the geometrical CAD operation is to be performed and including one or more of: a length, determined as a norm between the first point and the last point; a radius, determined as a distance between the center of the bounding box and the first point; a tension, determined as a norm of the tangent vector of the stroke divided by a norm of a tangent vector of the shape; a continuity level, determined as: G2 if the tangent vector of the stroke and the tangent vector of the shape are evaluated to be collinear and the normal vector of the stroke and a normal vector of the shape are evaluated to be collinear, G1 if the tangent vector of the stroke and the tangent vector of the shape are evaluated to be collinear and the normal vector of the stroke and the normal vector of the shape are evaluated to not be collinear, or G0 otherwise; a quadrant, determined as a couple of shape parts comprising the position of the stroke; and wherein, when the operation is a blend, a match or an extrapol operation, the parameter includes the continuity level and when the operation is a blend or a match operation, the parameter further includes the tension.