Printing methods and systems

A method of transferring an image onto a real surface of a real object, the method comprising:

• tracking position of a printing device on the real surface as the printing device is being moved over the real surface;
• using a CAD model of the object and extruded surfaces normal to a surface of the model at locations where the image should be printed;
• indicating a corresponding tracked position of the printing device on the surface of the CAD model;
• and
• commanding the printing device to print on the real surface whenever the tracked position on the CAD model crosses an extruded surface.

A system for transferring an image onto a real surface of a real object, the system comprising:

• a substance-depositing engine;
• a tracking device for tracking position of the substance-depositing engine as the engine is being moved over the real surface;
• and
• a computer programmed to use a computer-generated representation of the real surface, and extruded surfaces normal to the representation surface at locations where the image should be printed, wherein the representation is used to indicate the tracked position on the representation surface to represent the position of the substance-depositing engine on the real surface, and to command the engine to deposit a substance on the real surface whenever the tracked position on the representation surface crosses an extruded surface.