This paper tries to answer to the increasing demand for more intuitive methods for creating and modifying free-form curves and surfaces which is emerging in the field of conceptual design. We present a novel approach which adopts a simple 3D sketching technique together with a finite element deformation method to create free-form models. The method proposed lets the user interactively sculpt splines to modify a surface in a predicable way. Our algorithm automatically extracts the key points from the sketched "target curve" and it adaptively distributes the external-force constraints which impose the forces on the corresponding vertices along their normals. We have limited the influence of these constraints to a localized area by attaching an influence factor to each vertex of the parent surface. The smoothing function introduced later allows good control over the transition intervals and the symmetry features. The proposed method is finally implemented within a 3D environment and the results of its use show how the designers can intuitively and exactly control the shape of the sketched surface.
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