1. A computer based method for modifying a virtual model of a physical structure, comprising: (A) displaying an image of said virtual model on a display operatively connected to a computer system; (B) identifying at least a portion of said virtual model that is desired to be modified by interacting with the displayed image; and (C) modifying said virtual model by replacing in the computer system at least said portion of said virtual model with additional 3D data obtained from the physical structure to provide a modified virtual model.