The present invention provides a method whereby the spatial relationship and orientations of one or more three-dimensional objects being illuminated by an optical projector, and the optical projector itself, can be very accurately defined both quickly and easily. The present invention also provides a novel computerized optical projection system whereby three-dimensional data when viewed by the human eye projected onto three-dimensional objects is not deformed as a result of the non-planar projection surface. In one embodiment, the invention provides computerized optical assembly or manufacturing guidance systems, and related methods, that provide step-by-step assembly or manufacturing instructions for instructing technicians how to assemble or manufacture three-dimensional objects or systems. The assembly instructions are in the form of calibrated three-dimensional text, images and/or symbols, and are projected by one or a plurality of optical projectors that are in operable communication with one or a plurality of computers onto the three-dimensional objects or systems, or component parts or skins thereof.