A technique is disclosed for generating a new contour and/or a 3D surface such as a variational implicit surface from contour data. In one embodiment, B-spline interpolation is used to efficiently generate a new contour (preferably a transverse contour), from a plurality of input contours (preferably, sagittal and/or coronal contours). In another embodiment, a point reduction operation is performed on data sets corresponding to any combination of transverse, sagittal, or coronal contour data prior to processing those data sets to generate a 3D surface such as a variational implicit surface. A new contour can also be generated by the intersection of this surface with an appropriately placed and oriented plane. In this manner, the computation of the variational implicit surface becomes sufficiently efficient to make its use for new contour generation practical.