1. A system for augmented viewing of a patient target site in a surgical setting by a user, comprising: a computer for storing scan data of the patient target region, and for constructing from the stored data, a three dimensional perspective volumetric image of the target site as seen from a selected orientation; a viewing device, the device having a first ocular instrument and a second ocular instrument in which the patient target site can be viewed, and in which the three dimensional perspective volumetric image can be projected, forming a fused image using the patient target site view and the three dimensional perspective volumetric image; a tracking device coupled to the computer for tracking the selected orientation of the viewing device; and a calibration module in the computer for placing the viewing device in the same coordinate system as the patient in response to tracking information received from the tracking device, wherein the selected orientation from which the volumetric image of the target is constructed by the computer is the selected orientation of the second ocular instrument.