## 1 Introduction
[PERSON] and [PERSON] [28] presented a system and methodology for on-line free form surface measurement via a scanning contact probe installed on a CNC machine. To improve the measuring stability and continuity, FL control, in lieu of traditional PID control, is employed. The presented measuring system's main feature is that the number of measured points can vary with the change of surface curvature. Furthermore, [PERSON] _et al_. [29] reported on fuzzy-clustering-based reduction method, where as an effective extension to the existing pure geometric reduction methods, a hybrid heuristic is introduced. It includes descriptions of samples' fuzzy imperative attributes and fuzzy geometric attributes. Reduced points are favoured to gather in regions of high curvature and surface boundaries. Detailed features, which are particularly valuable for machining, can be well preserved. [PERSON] and [PERSON] [30] developed an RE system which processes photographs using ANN. The network was trained on a representative training set in order to be able to recognize novel forms. [PERSON] _et al_. [31] proposed a system which uses ANN for feature recognition in prismatic parts. [PERSON] _et al_. [32] presented an ANN approach used to find an optimal design space in order to improve precision and accuracy of RE models. [PERSON] and [PERSON] [33] reported on optimized re-triangulation based on GA. They described a method to generate optimized STL file (stereolithography CAD software file format developed by _3D Systems_) with reduced point data generated by laser scanning. The optimization is performed by reducing the number of triangles in STL file using triangles' vector normals. After extraction of triangles, re-triangulation is performed as in other reduction methods. [PERSON] and [PERSON] [34] analysed the application of GA in reduction of point data in polygonal models. Another example of application of GA in RE is given by [PERSON] _et al_. [35]. They presented an approach to simplification of meshed models using GA. Moreover, [PERSON] _et al_. [36] applied a hybrid approach, which combines ANN and GA, for the automatic registration of point clouds with free-form shapes. Amidst a number of developed approaches to point data reduction, three of them stand out as dominant: reduction by sampling, polygonal reduction, and mesh reduction [18, 19, 21, 37]. Point data reduction with the \"_cross-sectional_\" RE methodology, is primarily based on the so called sampling methods, amongst which the most popular are: factor-, spatial-, chord-, angle- and height methods [18, 19, 21, 38, 39]. All these methods use different parameters as criteria for point data reduction. However, the key indicator of quality of point data reduction methods is the ratio between the resulting deviation (of the cross-sectional curves, _i.e._, surface model) and the level (percentage) of data reduction. Accordingly, the underlying question of the so far investigations in this research area can be summarized as: _How to increase the level of data reduction, while simultaneously decreasing the error_, i.e., _the level of deviation?_  
The basic research objective of the study is the development of a system for quality pre-processing of 3D digitization data, which would satisfy current standards for accuracy in mechanical engineering. Special emphasis is placed on the development of a sub-system for the reduction of point data. The research is primarily focused on cross-sectional RE methodology and the results of digitization generated by the two, presently most widely used, systems for 3D digitization in mechanical engineering--contact scanning and optical triangulation. Bearing in mind that, from user's perspective, the abstract nature of parameters is a significant problem in reduction of point data using sampling methods, the second objective of this study is to develop an approach which would allow more user-friendly and intuitive interaction.