What if 3D printers understood the substrate onto which they were printing? Most printers simply print onto flat surfaces, and planning the deposition tool's path is simple because it is "painting a blank canvas." If printers, however, could fabricate directly onto complex geometries then they could repair objects, for example.  For this demonstration of in-situ repair, i.e. in-place repair, I started by printed a robot body out of epoxy. I then broke off one of the legs. Finally, I developed a printing method whereby the 3D printer laser scanned the robot, compared it to an image of the "healthy" robot, and then printed back the difference directly onto the broken robot.