For classic coordinate measuring machines, all measurement points required for analyzing the required features must be precisely defined before, or no later than during, the measurement process. This is not necessary for tomography. Because the entire work piece is captured, the stored data can even be used to calculate additional  dimensions at a later time. With a classic coordinate measuring machine, the physical work piece would need to be stored and measured again to achieve this goal. Risks include the long term stability of the work piece. In general, measuring with a classic coordinate measuring machine results in a much lower number of  measurement points recorded than for X-ray tomography. This results in a less complete description of the form of the geometric elements. Particularly for large form deviations, measurement errors can occur when determining the dimensions. The  basis  for  measuring  dimensions  using X-ray  tomography  is  always  the  complete tomography of the work piece, as described above, where all measurement points that describe the work piece are captured automatically. To calculate dimensions, the user simply needs to select the desired measurement points and calculate the resulting dimensions. In order to measure dimensions that are difficult to access or inaccessible (e.g. internal) dimensions, the user can virtually cut the part (CAD model and point cloud). The areas that are otherwise obscured are thus exposed and can be measured in the same manner as described above. If there are no CAD data available, the measurement points can be selected interactively by the user. They can be selected directly, using the mouse, or by the grouping of points by automatic segmentation into standard geometric elements. Starting from an initial point, surrounding points are automatically collected, for  example, until the form error of the selected element (e.g. cylinder) is significantly increased. This indicates that the boundaries of the element have been reached and the point selection process is stopped. In a similar manner, the entire point cloud can be segmented into standard geometric elements, such as planes and cylinders.  The elements thus determined can be selected to calculate additional dimensions, as is usual in coordinate measuring technology.

Seen in the image above: Measuring internal dimensions by virtual cutting: a) Internal cylinder wall, obscured b) Internal cylinder wall and associated point cloud from the CT measurement, exposed by removing the obscuring elements.