“…The main advantages regard the high accuracy of these instruments that can also provide the distribution of wear. As a disadvantage, they are slow and the specimen must be dismounted most of the time; they require the use of very expensive equipment and most of all the contact with the specimen’s surface can alter the wear characteristics.- Optical microscopy, 2D profilometry, and 3D scanning [23,24,25]: these methods imply the use of optical non-contact profilometers, 3D scanners, and microscopes. Optical 2D profilometers and 3D scanners can work according to the principles of optical range-finding techniques as, for example, confocal microscopy, time of flight, laser or structured light triangulation, photogrammetry, interferometry, etc.
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