# The Off-Line Simulation on Measuring through Software PC-DMIS CAD++ V4.3
## 4 Discussion
At the end of the measurement, the dimensions, shape deviations and positions of the substitute geometric elements are compared with the nominal values of the dimensions, shape deviations and positions of the scanned elements of the verified machine part. Depending on the method of scanning of points on the surface of the verified machine part, a tactile measurement on coordinate measuring machines can be divided into:  
Figure 13: Graphic display of the trajectory during the off-line simulation of the measuring program. (**a**) Complete display for the measuring position MPI; (**b**) detailed display for the measuring position MPI; (**c**) complete display for the measuring position MP2; (**d**) detailed display for the measuring position MP2. * Discontinuous tactile measurement (Figure 14a)--scanning tactile system is moved away from the surface of the component after scanning each point, and when scanning the next point, it is moved to the surface again,
* Continuous touch measurement--scanning (Figure 14b)--we can speak about scanning in connection with the measurement, when we investigate deviations in the shape of a certain scanned surface and also in connection with reverse engineering, in which we determine the shape of the unknown scanned surface with the goal of creating its parametric model in reverse mode. In both cases, the touch tip of the scanning system is in continuous contact with the surface of the verified machine part during the point scanning. In the presented paper, the verified machine part is the gearbox cover of the small tractor (Figure 15), for which it is necessary to prepare a measuring program. The disadvantage is the lack of a parametric model, which does not allow the creation of a measuring program by off-line programming and debugging by simulation. Since the number of elementary steps accompanies the creation of the repeatable and collision-free measuring program, it is appropriate to create a decomposition of the measuring task programming based on the analysis of the presented component (Figure 16). Figure 14: Methods of tactile measurement. (**a**) Discontinuous tactile measurement; (**b**) continuous tactile measurement—scanning; 1—touch tip of the scanning system; 2—point of tip contact with the surface of the measured part during discontinuous measurement and uninterrupted contact of touch tip with the surface of the measured part during scanning. Figure 15: Verified machine part—gearbox cover with marked zero point (ZP). The scanning system, of which the contact length and the tip diameter allows to scan all necessary points for its verification on the surface of the part without collision, is constructed based on the shape of the verified machine part and its monitored geometric specifications. In order to achieve accurate measurement results, it is required to move the scanning system to the point of tip contact with the surface of the measured object along a path parallel to the normal of the surface on which the scanning points are located. In order to be able to verify all geometrical specifications prescribed by the drawing while complying with the requirement, a basic orientation of the scanning system is not sufficient. At the beginning of the new measurement, the position of the verified part in the working space of the coordinate measuring machine is not clearly defined. In order to create a repeatable and collision-free measuring program and to achieve reliable measurement results, it is necessary to define the mutual position of the coordinate systems of the part and the coordinate measuring machine. The definition of the mutual position of coordinate systems is called alignment. 1. Alignment 3-2-1. \"Alignment 3-2-1\" can be included among the most basic and simplest ways of aligning the coordinate systems of a coordinate measuring machine \(O_{m}(x_{m},y_{m},z_{m})\) and the measured part \(O_{w}(x_{w},y_{w},z_{w})\).