Sketching out a freeform surface

This paper presents an intelligent algorithm on freeform surface interpretation based on four boundary curves, which are initially input with a 2D online sketch interface. The 2D strokes are filtered first and then the two pairs of curves are tidied up for compatibility and parameterisation. Detection of the principal dimensions of boundary curves and their configuration leads to 3D conversion of the 2D strokes. From the 3D curves, a bicubically blended Coons patch (base surface) is constructed. After that, design features such as cuts and offsets can be drawn directly on the 3D surface with gesture sketches. Finally, conceptual design surfaces can be output as exchange surfaces into commercial CAD packages for detailed design. This algorithm does not use explicit construction planes or reference surfaces for converting 2D strokes into 3D curves. Examples have shown that the proposed 3D interpretation algorithm is practical and useful.