Hand-sketching is a particularly attractive solution to providing an intuitive design interface for modeling . The goal is to reduce the data collected from the input strokes an d to construct a curve that faithfully represents the sketche d data . This paper presents a new approach to interactiv e realtime handsketching in two or three dimensions and isbased on the new approach to general spline datafittin g presented in [10,8,9] .

This paper describes a hidden curve algorithm specifically designed for sculptured surfaces. A technique is described to extract the visible curves for a given scene without the need to approximate the surface by polygons. This algorithm produces higher quality results than polygon based algorithms, as most of the output set has an exact representation. Surface coherence is used to speed up the process. Although designed for sculptured surfaces, this algorithm is also suitable for polygonal data.