A method is for estimating a three-dimensional (3D) representation of a set of two-dimensional (2D) curves of a concept drawing, the estimate of the 3D representation corresponding to a 3D object underlying the concept drawing. The method comprises: obtaining a representation of a set of 2D curves a concept drawing that represent a 3D object underlying the concept drawing; determining an energy function based on the set of 2D curves, the energy function comprising one or more terms, each term reflective of a preference for a 3D representation based on a characteristic of the 2D curves which reflects how concept drawings are commonly perceived to represent 3D objects; and performing an optimization which minimizes the energy function to thereby determine the 3D representation.