Abstract: A method of optically measuring the surface of yarn packages, wherein the package surface is scanned by a light beam, and the reflected light signal is evaluated. The light beam scans the package surface along a predefined path. At each predetermined measuring time, the light beam is directed to a scanning spot of the package surface, and the two plane coordinates of the scanning spot are determined. A portion of the light rays diffused from the scanning spot is focused and directed to a sensor, so that they arrive at the sensor in one point of incidence. The actual position of the point of incidence is measured, and from the difference between the actual position of the point of incidence and the desired point of incidence, the actual third, i.e. elevation, coordinate of the scanning spot may be determined.