It is not necessary to remove the stylus from the workpiece in order to measure several different surfaces of the same object. When combined with the appropriate control software, this principle provides the basis for automatic scanning of object surfaces (Fig. 21). The coordinate axes of the measuring machine are controlled so that the sensor always remains within its measuring range, thus following the surface of the workpiece when executing tangential movements. The control software moves the sensor in a virtual coordinate system whose origin is located at the point of contact between the probing element and the workpiece. If carried out as a control process, this results in the scanning of a circle in the example shown. Similarly, 3-D scanning can also be performed in predefined planes. However, in connection with three-dimensional surfaces, the problem of performing stylus sphere corrections on unknown surfaces must also be considered.