Geometric modeling is a key link in reverse engineering，the improvement of automation and generality of geometric modeling is a main direction of reverse engineering research. This kind of reverse engineering geometric modeling automation system has the characteristics of feature modeling which reflects the design intention, the organization of data points is not limited, the output b-rep model is fully compatible with the existing commercial CAD system. The key technology of the system is the automatic extraction of features, the smooth connection of the composite free surface.
CMM measurement can be divided into two categories: contact measurement and non-contact measurement. Contact measurement method records the coordinate position of sample’s surface by contacting with the sample, and it can be divided into point-triggering and continuous data acquisition methods. For aerospace, automobile and other industries, and measurement of large sample parts, in order to meet the precision requirement, we usually use the contact type. The point trigger measurement in contact type can be designed manually, it is possible to obtain more measurement points in areas with great curvature, and less points can be measured in relatively flat areas. In combination with the modeling method, the measurement of a workpiece can be planned manually according to its characteristics of different areas. Then we can get the main characteristics and curvilinear which affects shape of most. The data points can be organized according to requirement and rebuild a needed software. And then the CAD model of the object can be reconstructed according to line and curve’s characteristics and reduce the workload of data processing.
Non-contact measurement is mainly based on basic principle of optics, acoustics, magnetics, etc. A certain amount of physical simulation is converted into a coordinate point on the surface of the sample by means of an appropriate algorithm. For example, laser optical displacement measurement is to turn the laser flight time into the distance between the measured point and the reference plane. Due to the simple operation, the non-contact measurement technology represented by the laser ranging method has been developing rapidly and has become more and more widely used now.
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