An apparatus and method for generating a contour automatically based on one or more user-generated contours for a three dimensional (3D) structure. In one aspect, a method of integrating image contour generation and editing with contour interpolation and contour extrapolation is provided. Manual contour drawing and editing may be performed by a user while interpolation and/or extrapolation of contours is automatically calculated in the background. Results of the interpolation and/or extrapolation may be displayed immediately, allowing the user to easily make refinements to any contours, as needed. In one aspect, interpolated and extrapolated contours may be automatically adapted (e.g., recalculated) according to user-modifications of contours.